Lymphangioleiomyomatosis (LAM) is a rare, low-grade, multisystem neoplastic disorder that occurs almost exclusively in women, typically of childbearing age. It is a member of the perivascular epithelioid cell tumor (PEComa) family and is driven by biallelic inactivation of the tuberous sclerosis genes TSC1 or, far more commonly, TSC2, which removes the brake on mechanistic target of rapamycin complex 1 (mTORC1) signaling. The disease occurs in two contexts: a sporadic form (S-LAM) caused by somatic TSC2 mutations with loss of heterozygosity (a two-hit, tumor-like mechanism, not inherited), and a form associated with the heritable, autosomal-dominant tuberous sclerosis complex (TSC-LAM). LAM is characterized by the proliferation and lymphatic dissemination of abnormal smooth-muscle-like "LAM cells" that co-express smooth-muscle (smooth muscle actin, desmin) and melanocytic (HMB-45, Melan-A) markers and are estrogen- and progesterone-receptor positive. LAM cells infiltrate the lung and cause diffuse, bilateral cystic destruction of the parenchyma, progressive airflow obstruction, recurrent spontaneous pneumothorax, and chylous effusions from lymphatic involvement. Extrapulmonary manifestations include renal angiomyolipomas and axial lymphatic tumors (lymphangioleiomyomas). The female predominance reflects a central interaction between TSC2 loss and estrogen signaling. mTOR inhibitors (sirolimus, everolimus) are the established disease-modifying therapy, stabilizing lung function; serum VEGF-D is the principal diagnostic and treatment-response biomarker.
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Conditions with similar clinical presentations that must be differentiated from Lymphangioleiomyomatosis:
name: Lymphangioleiomyomatosis
creation_date: "2026-06-29T00:00:00Z"
description: >
Lymphangioleiomyomatosis (LAM) is a rare, low-grade, multisystem neoplastic
disorder that occurs almost exclusively in women, typically of childbearing
age. It is a member of the perivascular epithelioid cell tumor (PEComa) family
and is driven by biallelic inactivation of the tuberous sclerosis genes TSC1
or, far more commonly, TSC2, which removes the brake on mechanistic target of
rapamycin complex 1 (mTORC1) signaling. The disease occurs in two contexts: a
sporadic form (S-LAM) caused by somatic TSC2 mutations with loss of
heterozygosity (a two-hit, tumor-like mechanism, not inherited), and a form
associated with the heritable, autosomal-dominant tuberous sclerosis complex
(TSC-LAM). LAM is characterized by the proliferation and lymphatic
dissemination of abnormal smooth-muscle-like "LAM cells" that co-express
smooth-muscle (smooth muscle actin, desmin) and melanocytic (HMB-45, Melan-A)
markers and are estrogen- and progesterone-receptor positive. LAM cells
infiltrate the lung and cause diffuse, bilateral cystic destruction of the
parenchyma, progressive airflow obstruction, recurrent spontaneous
pneumothorax, and chylous effusions from lymphatic involvement.
Extrapulmonary manifestations include renal angiomyolipomas and axial
lymphatic tumors (lymphangioleiomyomas). The female predominance reflects a
central interaction between TSC2 loss and estrogen signaling. mTOR inhibitors
(sirolimus, everolimus) are the established disease-modifying therapy,
stabilizing lung function; serum VEGF-D is the principal diagnostic and
treatment-response biomarker.
category: Complex
disease_term:
preferred_term: Lymphangioleiomyomatosis
term:
id: MONDO:0011705
label: lymphangioleiomyomatosis
parents:
- Perivascular Epithelioid Cell Neoplasm
- mTOR Pathway Disorder
synonyms:
- LAM
- lymphangiomyomatosis
- pulmonary lymphangioleiomyomatosis
references:
- reference: PMID:20301399
title: "Tuberous Sclerosis Complex."
tags:
- GeneReviews
classifications:
harrisons_chapter:
- classification_value: RESPIRATORY
has_subtypes:
- name: Sporadic LAM
display_name: Sporadic lymphangioleiomyomatosis (S-LAM)
description: >
Occurs in women without tuberous sclerosis complex and is caused by somatic
(acquired) biallelic inactivation of TSC2 in LAM cells, with loss of
heterozygosity at the second allele (a two-hit, tumor-like mechanism). It is
not heritable.
- name: TSC-LAM
display_name: Tuberous sclerosis complex-associated lymphangioleiomyomatosis
description: >
Occurs in individuals with germline tuberous sclerosis complex; cystic lung
changes develop in roughly 30-40% of adult women with TSC, arising via a
somatic second hit on the wild-type TSC allele.
pathophysiology:
- name: TSC1/TSC2 Biallelic Inactivation
description: >
Biallelic loss of function of the tumor-suppressor genes TSC1 (hamartin) or,
far more commonly, TSC2 (tuberin). The TSC1-TSC2-TBC1D7 complex is a
GTPase-activating protein for the small GTPase RHEB; its loss removes a brake
on mTORC1. In sporadic LAM the two hits are somatic (mutation plus loss of
heterozygosity at 16p13.3); in TSC-LAM one allele is mutated in the germline
and a somatic second hit occurs in the LAM cell.
cell_types:
- preferred_term: LAM cell (smooth-muscle-like perivascular epithelioid cell)
term:
id: CL:0000192
label: smooth muscle cell
downstream:
- target: mTORC1 Hyperactivation
description: Loss of TSC1/TSC2 GAP activity elevates RHEB-GTP and constitutively activates mTORC1.
evidence:
- reference: PMID:18184959
reference_title: "Sirolimus for angiomyolipoma in tuberous sclerosis complex or lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "associated with mutations in tuberous sclerosis genes resulting in constitutive activation of the mammalian target of rapamycin (mTOR)"
explanation: >
Tuberous sclerosis gene mutations in LAM cause constitutive mTOR
activation, supporting the TSC1/TSC2-loss to mTORC1-hyperactivation edge.
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Our data demonstrate that somatic mutations in the TSC2 gene occur in the angiomyolipomas and pulmonary LAM cells of women with sporadic LAM, strongly supporting a direct role of TSC2 in the pathogenesis of this disease."
explanation: >
Establishes that somatic TSC2 mutations are present in the angiomyolipoma
and pulmonary LAM cells of women with sporadic LAM, defining the somatic
two-hit genetic basis of the disease.
- name: mTORC1 Hyperactivation
conforms_to: "deregulated_nutrient_sensing#mTORC1 Hyperactivation"
description: >
Loss of the TSC1/TSC2 GAP brake allows RHEB-GTP to accumulate and drives
constitutive activation of mTOR complex 1. mTORC1 increases cap-dependent
mRNA translation, ribosome biogenesis, anabolic metabolism, cell growth, and
survival while suppressing autophagy; it is the central, therapeutically
actionable node of LAM.
biological_processes:
- preferred_term: positive regulation of TOR signaling
modifier: INCREASED
term:
id: GO:0032008
label: positive regulation of TOR signaling
- preferred_term: autophagy
modifier: DECREASED
term:
id: GO:0006914
label: autophagy
downstream:
- target: Estrogen-Driven LAM Cell Survival and Dissemination
description: mTORC1-activated, tuberin-deficient cells are hormonally responsive; estrogen promotes their survival and spread.
- target: VEGF-D-Driven Lymphangiogenesis
description: mTORC1 hyperactivation increases VEGF-D production, driving lymphangiogenesis and lymphatic spread.
evidence:
- reference: PMID:18184959
reference_title: "Sirolimus for angiomyolipoma in tuberous sclerosis complex or lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Angiomyolipomas in patients with the tuberous sclerosis complex or sporadic lymphangioleiomyomatosis are associated with mutations in tuberous sclerosis genes resulting in constitutive activation of the mammalian target of rapamycin (mTOR)."
explanation: >
Establishes that tuberous sclerosis gene mutations in LAM and angiomyolipoma
result in constitutive mTOR activation, the central mechanism of the disease.
- name: Estrogen-Driven LAM Cell Survival and Dissemination
description: >
Tuberin-deficient LAM cells are estrogen- and progesterone-receptor
positive. Estrogen synergizes with mTORC1 activation to promote LAM cell
survival (resistance to anoikis), migration, and metastatic spread,
explaining why a constitutive genetic lesion produces a disease largely
restricted to reproductive-age women. Identical TSC2 mutations across
spatially separate lesions, and recipient-derived recurrence of LAM in
transplanted donor lungs, support a "benign metastasis" model.
cell_types:
- preferred_term: LAM cell (smooth-muscle-like perivascular epithelioid cell)
term:
id: CL:0000192
label: smooth muscle cell
biological_processes:
- preferred_term: estrogen receptor signaling pathway
modifier: INCREASED
term:
id: GO:0030520
label: estrogen receptor signaling pathway
- preferred_term: negative regulation of apoptotic process (anoikis resistance)
modifier: INCREASED
term:
id: GO:0043066
label: negative regulation of apoptotic process
downstream:
- target: Cystic Lung Destruction
description: Disseminated LAM cells seed the lung and proliferate around airways, vessels, and lymphatics.
evidence:
- reference: PMID:12411287
reference_title: "Recurrent lymphangiomyomatosis after transplantation: genetic analyses reveal a metastatic mechanism."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "histologically benign LAM cells can migrate or metastasize in vivo to the transplanted lung"
explanation: >
LAM cells migrate/metastasize in vivo to seed the lung, supporting the
dissemination-to-cystic-lung-destruction edge.
evidence:
- reference: PMID:12411287
reference_title: "Recurrent lymphangiomyomatosis after transplantation: genetic analyses reveal a metastatic mechanism."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "These data indicate that histologically benign LAM cells can migrate or metastasize in vivo to the transplanted lung."
explanation: >
Genetic analysis of recipient-derived LAM cells in a transplanted donor
lung demonstrates that histologically benign LAM cells migrate or
metastasize in vivo, supporting the metastatic ("benign metastasis") model.
- name: VEGF-D-Driven Lymphangiogenesis
description: >
mTORC1 hyperactivation increases production of vascular endothelial growth
factor D (VEGF-D), promoting lymphangiogenesis and lymphatic dissemination of
LAM cells. Elevated serum VEGF-D is the clinical correlate and serves as the
principal non-invasive diagnostic and treatment-response biomarker; it is
associated with lymphatic involvement.
cell_types:
- preferred_term: lymphatic endothelial cell
term:
id: CL:0002138
label: endothelial cell of lymphatic vessel
biological_processes:
- preferred_term: lymphangiogenesis
modifier: INCREASED
term:
id: GO:0001946
label: lymphangiogenesis
downstream:
- target: Cystic Lung Destruction
description: Lymphatic spread distributes LAM cells through the lung and axial lymphatics.
evidence:
- reference: PMID:22513045
reference_title: "Clinical utility of diagnostic guidelines and putative biomarkers in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "VEGF-D was associated with lymphatic involvement"
explanation: >
VEGF-D-associated lymphatic involvement supports lymphatic spread of LAM
cells as a route to lung disease.
evidence:
- reference: PMID:22513045
reference_title: "Clinical utility of diagnostic guidelines and putative biomarkers in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "VEGF-D was associated with lymphatic involvement"
explanation: >
Serum VEGF-D correlates with lymphatic involvement in LAM, supporting
VEGF-D-driven lymphangiogenesis as a disease mechanism and the use of
VEGF-D as a biomarker.
- name: Cystic Lung Destruction
description: >
Infiltrating LAM cells, together with recruited cells, produce
matrix-degrading enzymes (matrix metalloproteinases, cathepsin K) that
degrade elastin and extracellular matrix, leading to progressive, diffuse,
bilateral thin-walled cyst formation that replaces normal lung parenchyma and
produces progressive airflow obstruction and reduced gas transfer.
cell_types:
- preferred_term: LAM cell (smooth-muscle-like perivascular epithelioid cell)
term:
id: CL:0000192
label: smooth muscle cell
biological_processes:
- preferred_term: extracellular matrix disassembly
modifier: INCREASED
term:
id: GO:0022617
label: extracellular matrix disassembly
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Lymphangioleiomyomatosis (LAM) is a progressive and often fatal interstitial lung disease characterized by a diffuse proliferation of abnormal smooth muscle cells in the lungs."
explanation: >
Defines LAM as progressive lung disease characterized by diffuse
proliferation of abnormal smooth muscle cells, the basis of cystic lung
destruction.
phenotypes:
- name: Progressive Exertional Dyspnea
category: Respiratory
description: >
Progressive breathlessness on exertion is the dominant presenting symptom,
reflecting cystic lung destruction and airflow obstruction.
phenotype_term:
preferred_term: Exertional dyspnea
term:
id: HP:0002875
label: Exertional dyspnea
clinical_course: PROGRESSIVE
evidence:
- reference: PMID:20301399
reference_title: "Tuberous Sclerosis Complex."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Clinical screening for LAM symptoms (exertional dyspnea and shortness of breath) at each visit in females older than age 18 years"
explanation: >
Exertional dyspnea and shortness of breath are the cardinal LAM symptoms
screened for, supporting progressive exertional dyspnea as a manifestation.
- name: Pulmonary Cysts
category: Respiratory
description: >
Numerous bilateral, diffuse, thin-walled round cysts on high-resolution CT
are the defining and near-universal imaging feature of LAM.
phenotype_term:
preferred_term: Pulmonary cyst
term:
id: HP:0032445
label: Pulmonary cyst
evidence:
- reference: PMID:29140122
reference_title: "Lymphangioleiomyomatosis Diagnosis and Management: High-Resolution Chest Computed Tomography, Transbronchial Lung Biopsy, and Pleural Disease Management. An Official American Thoracic Society/Japanese Respiratory Society Clinical Practice Guideline."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "For women who have cystic changes on high-resolution computed tomography of the chest characteristic of LAM"
explanation: >
Cystic changes on high-resolution chest CT characteristic of LAM are the
defining pulmonary imaging feature of the disease.
- name: Spontaneous Pneumothorax
category: Respiratory
description: >
Spontaneous pneumothorax from rupture of subpleural cysts is frequently the
presenting event and is highly recurrent without pleurodesis.
phenotype_term:
preferred_term: Pneumothorax
term:
id: HP:0002107
label: Pneumothorax
temporality: RECURRENT
evidence:
- reference: PMID:31729820
reference_title: "Favorable survival even with high disease-specific complication rates in lymphangioleiomyomatosis after lung transplantation-long-term follow-up of a Japanese center."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "8 of 12 (67%) LAM patients encountered LAM-related complication including chylothorax and pneumothorax"
explanation: >
Pneumothorax is documented as a characteristic LAM-related complication in
this LAM cohort.
- name: Chylothorax
category: Respiratory
description: >
Chylous (triglyceride-rich) pleural effusion from lymphatic obstruction or
disruption; can be large and recurrent.
phenotype_term:
preferred_term: Chylothorax
term:
id: HP:0010310
label: Chylothorax
evidence:
- reference: PMID:31729820
reference_title: "Favorable survival even with high disease-specific complication rates in lymphangioleiomyomatosis after lung transplantation-long-term follow-up of a Japanese center."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "8 of 12 (67%) LAM patients encountered LAM-related complication including chylothorax and pneumothorax"
explanation: >
Chylothorax is documented as a characteristic LAM-related complication in
this LAM cohort.
- name: Renal Angiomyolipoma
category: Neoplasm
description: >
Benign fat-, vessel-, and smooth-muscle-containing renal PEComa, present in a
substantial fraction of sporadic LAM patients and the majority of TSC-LAM
patients; large lesions risk hemorrhage.
phenotype_term:
preferred_term: Renal angiomyolipoma
term:
id: HP:0006772
label: Renal angiomyolipoma
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Renal angiomyolipomas, which are found in most tuberous sclerosis patients, also occur in 60% of sporadic LAM patients."
explanation: >
Renal angiomyolipomas occur in 60% of sporadic LAM patients, establishing
this extrapulmonary manifestation and its frequency.
frequency: FREQUENT
- name: Hemoptysis
category: Respiratory
description: Usually mild blood-streaked sputum, attributable to lymphatic and vascular involvement.
phenotype_term:
preferred_term: Hemoptysis
term:
id: HP:0002105
label: Hemoptysis
- name: Cough
category: Respiratory
description: Chronic cough is a common respiratory symptom in LAM.
phenotype_term:
preferred_term: Cough
term:
id: HP:0012735
label: Cough
- name: Chronic Respiratory Failure
category: Respiratory
description: >
Advanced LAM progresses to hypoxemic respiratory failure and oxygen
dependence, with end-stage disease requiring consideration of lung
transplantation.
phenotype_term:
preferred_term: Respiratory failure
term:
id: HP:0002878
label: Respiratory failure
clinical_course: PROGRESSIVE
genetic:
- name: TSC2 Inactivation
gene_term:
preferred_term: TSC2
term:
id: hgnc:12363
label: TSC2
association: Biallelic Inactivating Mutations
variant_origin: GERMLINE_AND_SOMATIC
notes: >
TSC2 (tuberin; 16p13.3) is the dominant gene in LAM. In sporadic LAM the
lesions are somatic (mutation plus loss of heterozygosity at 16p13.3). In
TSC-LAM a germline TSC2 mutation is followed by a somatic second hit. Loss of
tuberin (loss of function of a tumor suppressor) produces a recessive,
cellular-level mTORC1 gain of activity.
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report the identification of somatic TSC2 mutations in five of seven angiomyolipomas from sporadic LAM patients."
explanation: >
Somatic TSC2 mutations were identified in angiomyolipomas from sporadic LAM
patients, establishing TSC2 as the principal causal gene.
- name: TSC1 Inactivation
gene_term:
preferred_term: TSC1
term:
id: hgnc:12362
label: TSC1
association: Biallelic Inactivating Mutations
variant_origin: GERMLINE_AND_SOMATIC
notes: >
TSC1 (hamartin; 9q34) is a less common driver of LAM than TSC2. Loss of
hamartin produces the same mTORC1 hyperactivation as loss of tuberin. TSC1
germline mutations cause a subset of tuberous sclerosis complex and thereby
TSC-LAM.
biochemical:
- name: Serum VEGF-D
biomarker_term:
preferred_term: VEGF-D
term:
id: NCIT:C172496
label: Vascular Endothelial Growth Factor D Measurement
notes: >
Serum VEGF-D is the principal non-invasive biomarker for LAM. In a woman with
characteristic cystic changes on HRCT, a serum VEGF-D level >=800 pg/mL is
considered diagnostic and can avoid lung biopsy. VEGF-D is elevated relative
to controls, correlates with lymphatic involvement, and falls with mTOR
inhibitor therapy, making it useful for monitoring treatment response.
evidence:
- reference: PMID:22513045
reference_title: "Clinical utility of diagnostic guidelines and putative biomarkers in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "VEGF-D was the strongest discriminator between patients and controls"
explanation: >
Serum VEGF-D was the strongest discriminator between LAM patients and
healthy controls, supporting its role as the key diagnostic biomarker.
- reference: PMID:22513045
reference_title: "Clinical utility of diagnostic guidelines and putative biomarkers in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Combining ERS criteria and serum VEGF-D reduces the need for lung biopsy in LAM."
explanation: >
Adding serum VEGF-D to clinical criteria reduces the need for lung biopsy,
establishing its diagnostic utility.
treatments:
- name: Sirolimus
description: >
Allosteric mTORC1 inhibitor (rapamycin) and the first-line, evidence-based
disease-modifying therapy for LAM. In the pivotal randomized MILES trial,
sirolimus stabilized FEV1, reduced serum VEGF-D, and improved symptoms and
quality of life; benefit reverses on discontinuation. It is indicated for
declining or impaired lung function and for problematic chylous effusions or
angiomyolipomas. The ATS/JRS guideline recommends sirolimus and VEGF-D
testing and recommends against doxycycline and hormonal therapy.
therapeutic_modality: SMALL_MOLECULE
target_mechanisms:
- target: mTORC1 Hyperactivation
treatment_effect: INHIBITS
description: >
Sirolimus (rapamycin) allosterically inhibits mTOR complex 1, directly
reversing the constitutive mTORC1 hyperactivation that drives LAM.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: sirolimus
term:
id: CHEBI:9168
label: sirolimus
evidence:
- reference: PMID:21410393
reference_title: "Efficacy and safety of sirolimus in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In patients with LAM, sirolimus stabilized lung function, reduced serum VEGF-D levels, and was associated with a reduction in symptoms and improvement in quality of life."
explanation: >
The randomized MILES trial established sirolimus as stabilizing lung
function and reducing VEGF-D in LAM.
- reference: PMID:27628078
reference_title: "Official American Thoracic Society/Japanese Respiratory Society Clinical Practice Guidelines: Lymphangioleiomyomatosis Diagnosis and Management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "These included recommendations for sirolimus treatment and vascular endothelial growth factor D testing and recommendations against doxycycline and hormonal therapy."
explanation: >
The ATS/JRS clinical practice guideline recommends sirolimus treatment and
VEGF-D testing while recommending against doxycycline and hormonal therapy.
- reference: PMID:20301399
reference_title: "Tuberous Sclerosis Complex."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Treatment with an mTOR inhibitor for enlarging SEGAs, intractable epilepsy, renal angiomyolipomas that are >4 cm, rapidly growing renal angiomyolipomas that are >3 cm, and LAM."
explanation: >
The Tuberous Sclerosis Complex GeneReviews (Management) lists mTOR-inhibitor
therapy for LAM among its targeted-therapy recommendations.
- name: Everolimus
description: >
Oral mTORC1 inhibitor used particularly for tuberous-sclerosis-associated
renal angiomyolipoma (where it produces tumor shrinkage) and as an
alternative to sirolimus.
therapeutic_modality: SMALL_MOLECULE
target_mechanisms:
- target: mTORC1 Hyperactivation
treatment_effect: INHIBITS
description: >
Everolimus inhibits mTOR complex 1, the constitutively activated node in
LAM, reducing angiomyolipoma volume and LAM-cell growth.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: everolimus
term:
id: CHEBI:68478
label: everolimus
evidence:
- reference: PMID:23312829
reference_title: "Everolimus for angiomyolipoma associated with tuberous sclerosis complex or sporadic lymphangioleiomyomatosis (EXIST-2): a multicentre, randomised, double-blind, placebo-controlled trial."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The angiomyolipoma response rate was 42% (33 of 79 [95% CI 31–53%])"
explanation: >
The randomized, placebo-controlled EXIST-2 trial demonstrated a 42%
angiomyolipoma response rate with everolimus (vs 0% placebo) in TSC- and
sporadic-LAM-associated angiomyolipoma.
- name: Pleurodesis
description: >
Chemical or surgical pleurodesis for recurrent (or even first-episode)
spontaneous pneumothorax and recurrent chylothorax, given the high recurrence
rate of pneumothorax in LAM. Guidelines support offering pleurodesis after
an initial pneumothorax rather than awaiting recurrence.
treatment_term:
preferred_term: surgical procedure
term:
id: MAXO:0000004
label: surgical procedure
evidence:
- reference: PMID:29140122
reference_title: "Lymphangioleiomyomatosis Diagnosis and Management: High-Resolution Chest Computed Tomography, Transbronchial Lung Biopsy, and Pleural Disease Management. An Official American Thoracic Society/Japanese Respiratory Society Clinical Practice Guideline."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "offering pleurodesis after an initial pneumothorax rather than postponing the procedure until the first recurrence"
explanation: >
The ATS/JRS guideline addendum recommends offering pleurodesis after an
initial pneumothorax in LAM given the high recurrence rate.
- name: Lung Transplantation
description: >
Definitive option for end-stage respiratory failure due to LAM, with good
outcomes; recipient-derived LAM can recur in the allograft but is usually
clinically indolent.
treatment_term:
preferred_term: organ transplantation
term:
id: MAXO:0010039
label: organ transplantation
evidence:
- reference: PMID:31729820
reference_title: "Favorable survival even with high disease-specific complication rates in lymphangioleiomyomatosis after lung transplantation-long-term follow-up of a Japanese center."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Lung transplantation (LT) is a reliable therapeutic option for end-stage pulmonary lymphangioleiomyomatosis (LAM)."
explanation: >
Lung transplantation is an established therapeutic option for end-stage
pulmonary LAM, with favorable long-term survival.
- name: Supportive Care
description: >
Supplemental oxygen, pulmonary rehabilitation, bronchodilators (for the
reversible component of obstruction), respiratory vaccinations, and dietary
management (low-fat/medium-chain-triglyceride diet) of chylous effusions.
Exogenous estrogen is generally avoided.
treatment_term:
preferred_term: Supportive Care
term:
id: NCIT:C15747
label: Supportive Care
inheritance:
- name: Sporadic (somatic, non-heritable)
description: >
Sporadic LAM is not inherited. It arises from somatic biallelic TSC2
inactivation in LAM cells (a two-hit, tumor-like mechanism), so there is no
transmission risk to offspring.
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In no case was the mutation present in normal kidney, morphologically normal lung, or lymphoblastoid cells."
explanation: >
The causal TSC2 mutations were absent from constitutional (lymphoblastoid)
DNA, confirming that sporadic LAM mutations are somatic, not germline, and
therefore not heritable.
- name: Autosomal dominant (TSC-LAM)
description: >
TSC-LAM occurs within tuberous sclerosis complex, which is autosomal dominant
(TSC1 or TSC2) with a high de novo mutation rate. LAM within TSC shows
incomplete, sex-biased penetrance (clinically penetrant mainly in women) and
variable expressivity, arising via a somatic second hit.
evidence:
- reference: PMID:10823953
reference_title: "Mutations in the tuberous sclerosis complex gene TSC2 are a cause of sporadic pulmonary lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "LAM can occur as an isolated disorder (sporadic LAM) or in association with tuberous sclerosis complex."
explanation: >
Establishes that LAM occurs both sporadically and in association with the
heritable, autosomal-dominant tuberous sclerosis complex (TSC-LAM).
prevalence:
- subtype: Sporadic LAM
population: Adult women
measure_type: POINT_PREVALENCE
prevalence_class: BAND_1_9_PER_1000000
rate_low: 0.3
rate_high: 0.8
percentage: ~3-8 per million women
notes: >
Sporadic LAM is rare, with commonly cited prevalence on the order of a few
per million adult women. TSC-LAM is more common within the TSC population.
- subtype: TSC-LAM
population: Adult women with tuberous sclerosis complex
measure_type: POINT_PREVALENCE
prevalence_class: ABOVE_1_IN_1000
rate_low: 30000.0
rate_high: 40000.0
percentage: ~30-40%
notes: Cystic lung changes of LAM develop in roughly one third of adult women with TSC.
progression:
- phase: Disease progression definition
notes: >
Disease progression is operationally defined as a >=10% absolute decline in
FEV1. Untreated, lung-function decline is substantial (the MILES placebo arm
showed an FEV1 slope of about -12 mL per month), is faster with higher VEGF-D
and worse histology, and tends to slow after menopause. mTOR inhibitors
stabilize but do not reverse decline, and progression resumes on
discontinuation.
evidence:
- reference: PMID:35717210
reference_title: "Long-term clinical course and outcomes in patients with lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Disease progression (DP) was defined as a 10% absolute decline in forced expiratory volume in one second (FEV1)."
explanation: >
Defines LAM disease progression as a 10% absolute decline in FEV1, the
standard progression endpoint.
diagnosis:
- name: High-resolution chest CT
description: >
HRCT showing numerous bilateral, diffuse, thin-walled round cysts with
normal intervening parenchyma is the cornerstone of LAM diagnosis. When
characteristic cysts are present without additional confirmatory features,
guidelines advise against diagnosing LAM on HRCT alone and support
transbronchial lung biopsy as a diagnostic tool.
evidence:
- reference: PMID:29140122
reference_title: "Lymphangioleiomyomatosis Diagnosis and Management: High-Resolution Chest Computed Tomography, Transbronchial Lung Biopsy, and Pleural Disease Management. An Official American Thoracic Society/Japanese Respiratory Society Clinical Practice Guideline."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "against making a clinical diagnosis of LAM on the basis of the high-resolution computed tomography findings alone and for considering transbronchial lung biopsy as a diagnostic tool"
explanation: >
The ATS/JRS guideline addendum addresses the role of HRCT and
transbronchial lung biopsy in establishing the diagnosis of LAM.
- name: Serum VEGF-D
description: >
Serum VEGF-D >=800 pg/mL in a woman with characteristic cystic HRCT changes
establishes the diagnosis of LAM without biopsy.
evidence:
- reference: PMID:22513045
reference_title: "Clinical utility of diagnostic guidelines and putative biomarkers in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Combining ERS criteria and serum VEGF-D reduces the need for lung biopsy in LAM."
explanation: Serum VEGF-D combined with clinical criteria reduces the need for diagnostic lung biopsy.
differential_diagnoses:
- name: Birt-Hogg-Dube syndrome
description: >
FLCN-related cystic lung disease with basilar/perimediastinal cysts,
fibrofolliculomas, and renal tumors; distinguished by cyst distribution and
germline FLCN testing. A leading diffuse cystic lung disease in the LAM
differential.
evidence:
- reference: PMID:39168181
reference_title: "Diffuse Cystic Lung Disease: A Clinical Guide to Recognition and Management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We focus on the DCLDs that are most likely to be encountered by practicing pulmonologists: lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, and lymphoid interstitial pneumonia."
explanation: >
Birt-Hogg-Dube syndrome is grouped with LAM among the principal diffuse
cystic lung diseases that must be distinguished from one another.
- name: Pulmonary Langerhans cell histiocytosis
description: >
Smoking-related cystic and nodular lung disease with upper-lobe predominance
and irregular/bizarre cysts, distinct from the uniform thin-walled round
cysts of LAM.
evidence:
- reference: PMID:39168181
reference_title: "Diffuse Cystic Lung Disease: A Clinical Guide to Recognition and Management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We focus on the DCLDs that are most likely to be encountered by practicing pulmonologists: lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, and lymphoid interstitial pneumonia."
explanation: >
Pulmonary Langerhans cell histiocytosis is grouped with LAM among the
principal diffuse cystic lung diseases requiring differentiation.
- name: Emphysema
description: >
Centrilobular/panlobular emphysema produces airspace destruction without true
cyst walls; smoking history and distribution distinguish it from LAM cysts.
animal_models:
- species: Mouse
genotype: Uterine-specific Tsc2 knockout
description: >
Conditional uterine-specific deletion of Tsc2 produces estrogen-dependent
myometrial proliferation and uterine leiomyomas, and Tsc2-null myometrial
tumors appear in the lungs of older animals, supporting a uterine origin and
metastatic pathogenesis for LAM. Myometrial growth and mTORC1/S6 activity are
abrogated by rapamycin or by elimination of sex-steroid production and are
restored by estrogen but not progesterone. Limitation: the model does not
reproduce human cystic lung destruction.
evidence:
- reference: PMID:23820898
reference_title: "Uterine-specific loss of Tsc2 leads to myometrial tumors in both the uterus and lungs."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "we found Tsc2 null myometrial tumors in lungs of older Tsc2 uterine-specific knockout females, suggesting that lung LAM-like myometrial lesions may indeed originate from the uterus."
explanation: >
Uterine-specific Tsc2-knockout mice develop Tsc2-null myometrial tumors in
the lungs, modeling the hormone-dependent, metastatic biology of LAM.
clinical_trials:
- name: NCT00414648
phase: PHASE_III
status: COMPLETED
description: >
MILES (Multicenter International LAM Efficacy of Sirolimus) - the pivotal
randomized, placebo-controlled trial of sirolimus in LAM that established
stabilization of lung function.
target_phenotypes:
- preferred_term: Exertional dyspnea
term:
id: HP:0002875
label: Exertional dyspnea
evidence:
- reference: PMID:21410393
reference_title: "Efficacy and safety of sirolimus in lymphangioleiomyomatosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In patients with LAM, sirolimus stabilized lung function, reduced serum VEGF-D levels, and was associated with a reduction in symptoms and improvement in quality of life."
explanation: >
The MILES randomized controlled trial demonstrated that sirolimus
stabilizes lung function in LAM.
notes: >
LAM is curated as a distinct, strongly multisystem disorder that is also
represented as the "Lymphangioleiomyomatosis" subtype of the
Perivascular Epithelioid Cell Neoplasm (PEComa) family entry and as a
pulmonary manifestation of Tuberous Sclerosis Complex. GeneReviews has no
standalone LAM chapter; the Tuberous Sclerosis Complex GeneReviews
(PMID:20301399) is the closest expert reference and covers TSC-LAM. The
GeneReviews-documented LAM features (cystic lung disease, exertional dyspnea,
renal angiomyolipoma, mTOR-inhibitor responsiveness) are captured here. The
MILES NCT identifier is recorded as registered on ClinicalTrials.gov; the
trial evidence is anchored to the published MILES report (PMID:21410393).
Overview. Lymphangioleiomyomatosis (LAM) is a rare, slowly progressive, low-grade neoplastic (metastasizing) disease that almost exclusively affects women, typically in their reproductive years. It is characterized by diffuse cystic destruction of the lung parenchyma, abnormal proliferation of immature smooth-muscle-like "LAM cells" along lymphatics, airways, and blood vessels, and a strong association with renal angiomyolipomas (AMLs) and chylous (lymphatic) effusions. It is now understood as a member of the PEComa family (perivascular epithelioid cell tumors) and behaves like a low-grade, hormonally responsive, metastasizing neoplasm — a "benign metastasizing" tumor of the lung ("a wolf in sheep's clothing," JCI 2012, https://www.jci.org/articles/view/58709).
Two clinical contexts exist: - Sporadic LAM (S-LAM): arises from somatic TSC2 mutations; not inherited. - TSC-LAM: occurs in patients with the germline disorder Tuberous Sclerosis Complex (TSC); affects up to 30–40% of adult women with TSC (and is detectable on CT in a substantial fraction of men with TSC, though usually asymptomatic).
Key identifiers: - MONDO: MONDO:0011705 (https://monarchinitiative.org/MONDO:0011705) - OMIM: #606690 — "LYMPHANGIOLEIOMYOMATOSIS; LAM" (https://omim.org/entry/606690) - Orphanet: ORPHA:538 - MedGen: C0751674 - ICD-10: J84.81 (Lymphangioleiomyomatosis); ICD-11: CB04.1 / under interstitial lung diseases (also coded among rare cystic lung diseases) - MeSH: D018192 "Lymphangioleiomyomatosis" - NCIT: C3725 (Lymphangioleiomyomatosis) - Related upstream gene disorders: TSC1 (OMIM 605284), TSC2 (OMIM 191092); Tuberous Sclerosis (OMIM 191100/613254)
Synonyms / alternative names: Lymphangiomyomatosis; LAM; pulmonary lymphangioleiomyomatosis; lymphangiomyoma; sporadic lymphangioleiomyomatosis (S-LAM); tuberous-sclerosis–associated LAM (TSC-LAM). (Note: "lymphangiomyomatosis" is the legacy OMIM/ClinVar spelling.)
Data derivation: Disease-level resource (aggregated). LAM knowledge derives from disease-level registries and natural-history cohorts (NHLBI LAM Registry, the LAM Foundation registry, Japanese national insurance-claims database, ERS/ATS guideline cohorts) rather than single-patient EHR records.
Sources: OMIM 606690 (https://omim.org/entry/606690); Monarch MONDO:0011705; StatPearls (https://www.ncbi.nlm.nih.gov/books/NBK534231/); clinical review, Breathe 2020 (https://publications.ersnet.org/content/breathe/16/2/200007); PMC7714539 (https://pmc.ncbi.nlm.nih.gov/articles/PMC7714539/).
Primary cause — genetic/mechanistic. LAM is caused by biallelic inactivation of the tumor-suppressor genes TSC1 (9q34, encoding hamartin) or, far more commonly, TSC2 (16p13.3, encoding tuberin). Loss of the TSC1–TSC2–TBC1D7 complex (a GTPase-activating complex for the small GTPase RHEB) leads to constitutive activation of mTOR complex 1 (mTORC1), driving inappropriate cell growth, proliferation, survival, and lymphangiogenesis.
Risk factors: - Female sex — overwhelmingly the dominant risk factor; near-exclusive female predominance. - Reproductive-age / hormonal status — onset and progression cluster in the premenopausal period; estrogen is a key disease driver (see §5). - Germline TSC1/TSC2 mutation (Tuberous Sclerosis Complex) — strongest genetic risk factor; TSC raises LAM risk dramatically. - Family history — only relevant via TSC (sporadic LAM is not heritable). - Pregnancy and exogenous estrogen — associated with accelerated progression and pneumothorax risk in observational data; estrogen-containing contraceptives are generally cautioned against.
Protective factors: - Menopause / estrogen withdrawal is associated with slower decline; lung-function decline tends to attenuate after menopause. - No validated genetic protective variants are established. Anti-estrogen states (oophorectomy historically attempted) were proposed as protective but lack robust trial support.
Gene–environment interaction. The central interaction is TSC2 loss × estrogen signaling: tuberin-deficient cells are hormonally responsive; estrogen promotes LAM-cell survival (via inhibition of anoikis), migration, MEK–ERK signaling, and pulmonary metastasis in preclinical models (see §6 and §15). This explains why a constitutive genetic lesion produces a sex- and reproductive-stage-restricted disease.
Sources: OMIM 606690; PMC7714539; AJP Cell Physiol 2022 (https://journals.physiology.org/doi/full/10.1152/ajpcell.00202.2022); Karbowniczek 2003.
LAM is a multisystem disease dominated by pulmonary, lymphatic, and renal manifestations. Approximate frequencies below are drawn from registry/cohort literature (NHLBI LAM Registry; ATS/JRS guideline; Orphanet).
| Phenotype | Type | Suggested HPO | Approx. frequency | Notes / characteristics |
|---|---|---|---|---|
| Progressive exertional dyspnea | Symptom | HP:0002875 (Exertional dyspnea) / HP:0002094 (Dyspnea) | Very frequent (~70–80%) | Adult-onset; progressive; the dominant presenting symptom |
| Spontaneous pneumothorax | Clinical sign/event | HP:0002107 (Pneumothorax) | ~50–70% over disease course; recurrent | Often the presenting event; recurrence rate very high (~70% without pleurodesis) |
| Diffuse pulmonary cysts (thin-walled, bilateral) | Imaging/physical | HP:0009789 (Pulmonary cyst) / HP:0032967 (Cystic lung disease, verify) | ~Universal (defining) | Bilateral, diffuse, round, thin-walled; uniform distribution |
| Chylothorax | Clinical sign | HP:0030758 (Chylothorax, verify) / HP:0010310 (Chylous pleural effusion) | ~10–30% | Due to lymphatic obstruction; can be recurrent/large |
| Chylous ascites / chyluria | Clinical sign | HP:0030245 (Chylous ascites, verify) | Less common | Lymphatic involvement of abdomen |
| Renal angiomyolipoma | Tumor/sign | HP:0006772 (Renal angiomyolipoma, verify) / HP:0009592 (Angiomyolipoma) | ~30–50% (S-LAM); up to ~80–90% (TSC-LAM) | Risk of hemorrhage if >4 cm or aneurysm >5 mm |
| Lymphangioleiomyoma (cystic lymphatic mass) | Tumor/sign | HP:0100763 (Lymphangioma, verify) | ~16–40% | Retroperitoneal/pelvic; may fluctuate in size diurnally |
| Hemoptysis | Symptom | HP:0002105 (Hemoptysis) | Occasional | Usually mild |
| Cough | Symptom | HP:0012735 (Cough) | Frequent | |
| Airflow obstruction (↓FEV₁, ↓FEV₁/FVC) | Lab/PFT | HP:0006510 (Chronic pulmonary obstruction, verify) / HP:0030877 (Reduced FEV1, verify) | Frequent, progressive | Obstructive pattern; reduced DLCO is common and often early |
| Reduced DLCO | Lab/PFT | HP:0045051 (Abnormal DLCO, verify) | Frequent | Sensitive early marker |
| Chronic respiratory failure / hypoxemia | Sign | HP:0002878 (Respiratory failure) / HP:0012418 (Hypoxemia) | Advanced disease | End-stage |
| Elevated serum VEGF-D | Lab abnormality | (no specific HP) | Frequent (diagnostic) | >800 pg/mL is diagnostic in correct context (see §10) |
| Fatigue / reduced exercise capacity | Symptom | HP:0012378 (Fatigue) | Frequent | Reduced 6-minute-walk distance |
Quality-of-life impact: Progressive dyspnea, oxygen dependence, recurrent pneumothorax/effusions, and the emotional burden of a rare progressive disease substantially reduce HRQoL. Lung-function decline and 6-minute-walk distance correlate with QoL and mortality (Determinants of Progression and Mortality, Chest 2023, https://www.sciencedirect.com/science/article/pii/S0012369223002726).
Sources: ATS/JRS guideline PMID:27628078; Orphanet ORPHA:538; Breathe 2020 review; StatPearls.
Causal genes: - TSC2 — 16p13.3, encodes tuberin; HGNC:12363; OMIM 191092. The dominant gene in sporadic LAM. - TSC1 — 9q34, encodes hamartin; HGNC:12362; OMIM 605284. Rarely implicated in sporadic LAM; more in TSC.
The TSC1–TSC2–TBC1D7 complex is the GAP for RHEB-GTP; loss → RHEB-GTP accumulation → mTORC1 hyperactivation.
Pathogenic variants: - Variant types: the full spectrum of loss-of-function lesions — nonsense, frameshift (indels), splice-site, missense, large deletions/structural rearrangements, plus second-hit LOH at 16p13. ClinVar examples include TSC2 c.501G>A (p.Trp167Ter) nonsense and TSC2 c.5160+4A>C splice variants annotated to "Lymphangiomyomatosis" (https://www.ncbi.nlm.nih.gov/clinvar/RCV001195824/, RCV001196213/). - Classification: Per ACMG/AMP, truncating LoF variants in TSC2 are typically Pathogenic/Likely Pathogenic; many missense are VUS. - Somatic vs germline: Somatic in S-LAM (with LOH); germline + somatic second hit in TSC-LAM. Somatic mosaicism for TSC2 has been documented even in isolated/"sporadic" LAM, including rare male cases (PMC10849871; PMC7340110 "Generalised mosaicism for TSC2 mutation in isolated lymphangioleiomyomatosis"). - Functional consequence: Loss of function of tuberin (a tumor suppressor) → mTORC1 gain of activity (a "two-hit," recessive-at-cellular-level mechanism). - Allele frequency: Causal somatic mutations are private/not in population databases; germline TSC variants in gnomAD are exceedingly rare.
Modifier genes / interacting loci: Estrogen-receptor-α (ESR1) signaling, Wnt/β-catenin, and downstream effectors modulate phenotype; no formal Mendelian modifier gene is established. mTORC1 hyperactivation cross-talks with ERα, Wnt, FGF, SHH, and TGFβ signaling to produce the cystic phenotype (PMC7714539; AJP Cell Physiol 2022).
Epigenetics: A 3D drug-screen study implicated HDAC dependency in mTORC1-driven LAM, nominating HDAC inhibitors (bioRxiv 2021, https://www.biorxiv.org/content/10.1101/2021.07.03.451004). Epigenetic regulation is an emerging but not yet clinically actionable area.
Chromosomal abnormalities: No recurrent karyotypic aberration beyond locus-specific LOH at 16p13 (TSC2) detected in microdissected LAM cells.
Sources: OMIM 606690/191092; ClinVar TSC2 records; PMC10849871; PMC7340110; Carsillo/Henske PNAS 2000 (PMID:10737804, verify).
Sources: PMC6293523; ATS/JRS guideline; Endocrinology minireview (https://academic.oup.com/endo/article/157/9/3374/2422360).
Central causal chain (upstream → downstream):
Cellular processes: dysregulated cell growth/proliferation, evasion of anoikis/apoptosis, autophagy modulation (mTORC1 suppresses autophagy — basis for the sirolimus + autophagy-inhibition trials, PMC6026235), metabolic reprogramming, lymphangiogenesis, ECM proteolysis. The proapoptotic protein Bim mediates anoikis that estrogen overcomes (PMC5111508). Estradiol also augments tumor-induced neutrophil production to promote metastasis (PMC10164661).
Cell of origin: Uncertain but converging on a uterine/neural-crest-related smooth-muscle lineage. Uterine-specific Tsc2 deletion in mice produces myometrial tumors that spontaneously metastasize to lung (PMC3753421; "Identification of the lymphangioleiomyomatosis cell and its uterine origin," bioRxiv). LAM cells co-express melanocytic (HMB-45, gp100, Melan-A, MITF) and smooth-muscle (SMA, desmin) markers, plus ERα/PgR, consistent with a neural-crest–related, PEComa lineage (Frontiers 2014, PMC4243694).
Suggested ontology terms (mechanism): - GO: GO:0032008 (positive regulation of TOR signaling), GO:0031929 (TOR signaling), GO:0001525 (angiogenesis), GO:0001946 (lymphangiogenesis), GO:0030198 (extracellular matrix organization), GO:0043066 (negative regulation of apoptotic process), GO:0006914 (autophagy). - CL: CL:0000192 (smooth muscle cell), CL:0000669 (pericyte, verify), CL:0000148 (melanocyte, partial-marker analogy), CL:0002138 (endothelial cell of lymphatic vessel). - CHEBI: CHEBI:9168 (sirolimus), CHEBI:16469 (17β-estradiol), CHEBI:50845 (doxycycline), CHEBI:68481 (everolimus, verify), CHEBI:42261 (rapamycin synonym).
Sources: PMC7714539; PMC10523142; AJP Cell Physiol 2022; PMC4992946; PMC5111508; PMC10164661; PMC3753421; PMC4243694; PMC6026235.
Tissue/cell level: - Affected tissue: smooth muscle / mesenchymal connective tissue, lymphatic and pulmonary epithelium (secondary). - Target cell: the LAM cell — a perivascular epithelioid cell with spindle (smooth-muscle-like, SMA/desmin+) and epithelioid (HMB-45/Melan-A+) morphologies; ERα/PgR positive. CL: CL:0000192 (smooth muscle cell); melanocytic differentiation (CL:0000148 melanocyte) as marker analogy.
Subcellular: mTORC1 signaling node at the lysosomal membrane (GO:0005765); cytoplasmic translational machinery (ribosome, GO:0005840); nucleus (ERα transcriptional program, GO:0005634).
Localization / laterality: Pulmonary disease is bilateral and diffuse/symmetric; pneumothorax may be unilateral at presentation; angiomyolipomas often bilateral.
Sources: ATS/JRS guideline; StatPearls; Molecular Pathology of LAM/PEComa (https://meridian.allenpress.com/aplm/article/134/1/33/460876).
Sources: MILES PMID:21410393; Predicting Individualized Progression, Chest 2023 (PMC10258438); Natural History (PMC2883494); Long-term outcomes PMID:35717210.
Epidemiology: - Prevalence (S-LAM): ~3–8 per million women; commonly cited ~1 in 400,000 adult women. Japanese national-database data (2019): prevalence ~28.7 per million women, incidence ~3 per million women-years (ScienceDirect, J Investig Med?/ ERJ Open?, https://www.sciencedirect.com/science/article/abs/pii/S2212534524000522). - Men: incidence <0.2/million-yr, prevalence ~0.8/million (essentially only in TSC). - TSC-LAM: cystic lung changes occur in ~30–40% of adult women with TSC (higher with age).
Inheritance pattern: - Sporadic LAM: NOT inherited (somatic two-hit, like a tumor). - TSC-LAM: Tuberous Sclerosis is autosomal dominant (TSC1/TSC2), with high spontaneous-mutation rate (~⅔ de novo); LAM then arises via somatic second hit. Penetrance of LAM within TSC is incomplete and sex-biased (clinically penetrant mainly in women). Variable expressivity is the rule. - Germline/somatic mosaicism: documented (relevant to rare apparent-sporadic and male cases). - Anticipation, founder effects, consanguinity, carrier frequency: Not applicable to sporadic LAM; standard TSC genetics apply to TSC-LAM.
Demographics: - Sex ratio: Overwhelmingly female (sporadic LAM essentially female-only; very rare male cases reported, usually with TSC or mosaicism). - Age: Predominantly reproductive-age women (20s–40s) at diagnosis. - Ethnic/geographic: No strong ethnic predilection; reported worldwide. Apparent regional differences largely reflect ascertainment.
Sources: Japan national database study (S2212534524000522); Orphanet ORPHA:538; Medscape (https://emedicine.medscape.com/article/299545-overview); StatPearls.
Imaging (cornerstone): - HRCT chest: numerous, bilateral, diffuse, thin-walled round cysts with normal intervening parenchyma — characteristic and often diagnostic in the right clinical context (RadLex; ATS/JRS guideline). Abdominal CT/MRI for AMLs and lymphangioleiomyomas.
Biomarker: - Serum VEGF-D — the key non-invasive diagnostic test. ≥800 pg/mL in a woman with characteristic cystic HRCT is diagnostic of LAM (avoids biopsy); a cut-off ~645 pg/mL is sensitive, ~800 pg/mL is specific (PLOS One, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212776; Young et al., Respir Res 2012, PMID:22513045 — "combining ERS criteria and serum VEGF-D reduc[es] the need for lung biopsy"). VEGF-D also tracks treatment response (falls on sirolimus) and correlates with lymphatic involvement.
Other supportive tests: - PFTs: obstructive pattern (↓FEV₁, ↓FEV₁/FVC), reduced DLCO; air trapping. Used for staging and monitoring. - 6-minute walk test, pulse oximetry for functional staging. - Pleural fluid analysis: chylous (triglyceride-rich) effusion.
Histopathology / biopsy (when imaging+biomarker inconclusive): - Transbronchial lung biopsy (often diagnostic; 2017 ATS/JRS addendum supports it, PMC5694834) or surgical biopsy. - Microscopy: nodular/diffuse proliferation of spindle and epithelioid smooth-muscle-like cells around cysts, lymphatics, and vessels. - Immunohistochemistry: HMB-45 positive (~most sensitive melanocytic marker for LAM cells), SMA/desmin positive, ERα and PgR positive; Melan-A, MITF, cathepsin-K may be positive. (Molecular Pathology of LAM/PEComa, Allenpress 2010.)
Genetic testing: - Indicated to evaluate for TSC (germline TSC1/TSC2 panel/sequencing + deletion/duplication analysis) when TSC features are present or in younger/multifocal disease. Sporadic LAM is diagnosed clinically (HRCT + VEGF-D ± biopsy); somatic TSC2 testing of lesional tissue is research-oriented.
Diagnostic criteria: ATS/JRS 2016 and ERS 2010 criteria integrate characteristic HRCT + at least one of: AML, chylous effusion, lymphangioleiomyoma, TSC, or serum VEGF-D ≥800 pg/mL (or confirmatory biopsy).
Differential diagnosis: Birt-Hogg-Dubé syndrome (basilar cysts, FLCN), pulmonary Langerhans cell histiocytosis (smoking, upper-lobe nodules/cysts), emphysema/COPD, Sjögren-associated LIP/cystic disease, amyloidosis, light-chain deposition disease, follicular bronchiolitis. VEGF-D and cyst morphology distinguish LAM.
Suggested MAXO/diagnostic terms: MAXO:0000455 (chest CT, verify); biomarker assay; histopathology examination (MAXO:0000823, verify).
Sources: ATS/JRS 2016 (PMID:27628078); 2017 addendum (PMC5694834); Summary for Clinicians (PMC5566288); VEGF-D PLOS One 2019; Young 2012 (PMID:22513045).
Sources: PMID:35717210; Chest 2023 (S0012369223002726); MILES PMID:21410393; Lung Transplantation NEJM 1996 (https://www.nejm.org/doi/full/10.1056/NEJM199610243351704).
Pharmacotherapy (disease-modifying): - Sirolimus (rapamycin) — allosteric mTORC1 inhibitor; first-line, evidence-based therapy. The pivotal MILES trial (RCT, n=89, NEJM 2011, PMID:21410393) showed sirolimus stabilized FEV₁ (slope +1 vs −12 mL/month placebo), reduced VEGF-D, and improved symptoms/QoL — "sirolimus stabilized lung function, reduced serum VEGF-D levels, and was associated with a reduction in symptoms and improvement in quality of life." Benefit reverses on cessation. Indicated for FEV₁ <70% predicted, rapid decline, or problematic chylous effusions/AML. MAXO: pharmacotherapy; CHEBI:9168 (sirolimus); therapeutic_modality: SMALL_MOLECULE. - Everolimus — second mTORC1 inhibitor; used especially for renal angiomyolipoma (EXIST-2 trial established AML shrinkage with everolimus; FDA-approved for TSC-associated AML) and as a sirolimus alternative. CHEBI:68481 (verify). - Doxycycline — anti-MMP rationale; trials (e.g., the UK doxycycline trial) showed no clear lung-function benefit; not routinely recommended (ATS/JRS: do not use to improve lung function). - Hormonal manipulation (anti-estrogen, progesterone, GnRH analogs, oophorectomy): historically used; not recommended by ATS/JRS due to lack of efficacy and harms; avoid exogenous estrogen.
Pharmacogenomics: No validated pharmacogenomic dosing for sirolimus in LAM beyond therapeutic drug monitoring (target trough ~5–15 ng/mL, often lower in LAM ~5–10).
Experimental / advanced therapeutics (clinical trials): - Sirolimus + autophagy inhibition (hydroxychloroquine) — SAIL phase I (PMC6026235, NCT01687179). - Resveratrol + sirolimus — RESET trial (NCT03253913). - Aromatase inhibitors (letrozole) — TRAIL trial in postmenopausal LAM. - HDAC inhibitors — preclinical lead (bioRxiv 2021). - Other mTOR/autophagy/anti-estrogen combinations and inhaled sirolimus are under study.
Supportive / interventional: - Pleurodesis (chemical or surgical) for recurrent pneumothorax/chylothorax; pleurodesis is preferred even after a first pneumothorax given high recurrence (ATS/JRS). - Embolization or nephron-sparing surgery for large/bleeding renal AML (>4 cm or aneurysm >5 mm). - Supplemental oxygen, pulmonary rehabilitation, bronchodilators (some have reversible obstruction), vaccinations, dietary management of chylous effusions (low-fat/MCT diet). - Lung transplantation for end-stage disease (MAXO:0010039 organ transplantation).
Treatment outcomes: Sirolimus stabilizes FEV₁ and reduces VEGF-D in the majority; common adverse events: mucositis/stomatitis, acne-like rash, hyperlipidemia, edema, cytopenias, infections, diarrhea. Real-world data confirm durable stabilization with continued therapy (PMC10713282, "mTOR inhibitors in real world").
Suggested MAXO terms: MAXO:0000058 (pharmacotherapy/therapeutic, verify; or NCIT:C15986 Pharmacotherapy), MAXO:0010039 (organ transplantation), MAXO:0000950 (supportive care), MAXO:0000004/NCIT:C15329 (surgical procedure for pleurodesis/AML), MAXO:0000506 (oxygen therapy, verify).
Sources: MILES PMID:21410393; ATS/JRS 2016 PMID:27628078; PMC10713282; PMC6026235; clinicaltrials.gov NCT03253913, NCT01687179.
Sources: ATS/JRS guideline; PMC10327335; TSC surveillance consensus.
Sources: Eker-rat literature; OMIA; PMC4992946.
Mouse models: - Uterine-specific Tsc2 knockout (conditional, e.g., Amhr2-Cre or progesterone-receptor-Cre driven): produces estrogen-dependent myometrial tumors with smooth-muscle and neural-crest features that spontaneously metastasize to lung* in ~50% of animals — the best genetic recapitulation of LAM's hormone dependence and lung tropism (PMC3753421; Molecular Endocrinology 2013). Strong support for the uterine-origin/metastasis hypothesis. - Tsc1/Tsc2 heterozygous mice develop renal and hepatic tumors (TSC-like) but do not faithfully reproduce pulmonary LAM* — a key limitation.
Rat model: - Eker rat (germline Tsc2 mutation) — source of the widely used ELT3 (Eker leiomyoma–derived) cell line, TSC2-null smooth-muscle cells expressing ERα/PgR.
Cell-line / xenograft models: - ELT3 cells and TSC2-null/patient-derived AML cells used in xenograft "pseudo-LAM" lung-metastasis assays. Estrogen strongly enhances pulmonary metastasis of ELT3 cells, via MEK1/2–ERK1/2 signaling, anoikis resistance (Bim suppression), and estradiol-driven neutrophil expansion (Discover Oncology 2014; PMC5111508; PMC10164661). - Patient-derived LAM cells / iPSC and 3D/organoid drug-screen systems — used for therapeutic screening (HDAC inhibitor lead, bioRxiv 2021).
Genetic-model types available: knockout (constitutive Tsc1/Tsc2 het), conditional/tissue-specific knockout (uterine Tsc2), spontaneous-mutant (Eker rat), and xenograft/induced metastasis models.
Phenotype recapitulation: Uterine-Tsc2-KO mouse captures hormone dependence, smooth-muscle/melanocytic marker profile, and spontaneous lung metastasis; ELT3 xenografts capture estrogen-driven metastasis and mTORC1 biology and respond to rapamycin. Limitations: no model fully reproduces human cystic lung destruction, the chronic indolent clinical course, or the exclusively female human epidemiology; lung "metastases" are myometrial-tumor deposits rather than authentic cyst-forming LAM lesions.
Applications: dissecting mTORC1 signaling, estrogen/ERα–mTOR crosstalk, anoikis/metastasis biology, and preclinical drug testing (rapamycin/everolimus, anti-estrogens, autophagy and HDAC inhibitors).
Resources/databases: MGI (mouse Tsc1/Tsc2), RGD (rat Tsc2, Eker), Cellosaurus (ELT3), ATCC; Alliance of Genome Resources.
Sources: PMC3753421; Discover Oncology 2014 (https://link.springer.com/article/10.1007/s12672-014-0192-z); PMC4992946; PMC5111508; PMC10164661; bioRxiv 2021.
Sources (search-derived URLs): - https://pmc.ncbi.nlm.nih.gov/articles/PMC7714539/ - https://journals.physiology.org/doi/full/10.1152/ajpcell.00202.2022 - https://pmc.ncbi.nlm.nih.gov/articles/PMC10523142/ - https://pmc.ncbi.nlm.nih.gov/articles/PMC10713282/ - https://pubmed.ncbi.nlm.nih.gov/21410393/ - https://www.nejm.org/doi/full/10.1056/NEJMoa1100391 - https://pmc.ncbi.nlm.nih.gov/articles/PMC6026235/ - https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212776 - https://pubmed.ncbi.nlm.nih.gov/22513045/ - https://www.sciencedirect.com/science/article/abs/pii/S2212534524000522 - https://emedicine.medscape.com/article/299545-overview - https://www.ncbi.nlm.nih.gov/books/NBK534231/ - https://publications.ersnet.org/content/breathe/16/2/200007 - https://meridian.allenpress.com/aplm/article/134/1/33/460876 - https://pmc.ncbi.nlm.nih.gov/articles/PMC10258438/ - https://www.nejm.org/doi/full/10.1056/NEJM199610243351704 - https://pubmed.ncbi.nlm.nih.gov/35717210/ - https://www.sciencedirect.com/science/article/pii/S0012369223002726 - https://www.jci.org/articles/view/58709 - https://pmc.ncbi.nlm.nih.gov/articles/PMC4992946/ - https://academic.oup.com/endo/article/157/9/3374/2422360 - https://pmc.ncbi.nlm.nih.gov/articles/PMC5111508/ - https://pmc.ncbi.nlm.nih.gov/articles/PMC10164661/ - https://link.springer.com/article/10.1007/s12672-014-0192-z - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3753421/ - https://www.atsjournals.org/doi/full/10.1164/rccm.200208-969OC - https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2014.00069/full - https://omim.org/entry/606690 - https://monarchinitiative.org/MONDO:0011705 - https://pmc.ncbi.nlm.nih.gov/articles/PMC5694834/ - https://pmc.ncbi.nlm.nih.gov/articles/PMC5566288/ - https://www.biorxiv.org/content/10.1101/2021.07.03.451004 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10849871/ - https://pmc.ncbi.nlm.nih.gov/articles/PMC7340110/ - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10327335/
Curator handoff note: This is the worktree branch add-lymphangioleiomyomatosis with an untracked kb/disorders/Lymphangioleiomyomatosis.yaml. The highest-value, well-anchored evidence items for the KB entry are: (1) MILES/sirolimus (PMID:21410393), (2) ATS/JRS guideline + VEGF-D 800 pg/mL threshold (PMID:27628078; PMID:22513045), (3) TSC2/mTORC1 LOH mechanism (PMID:10737804), (4) metastatic/recurrence-after-transplant model (Karbowniczek 2003), and (5) uterine-Tsc2-KO mouse model (PMC3753421). Before committing any of these as snippets, run just fetch-reference PMID:XXXX and verify each quote is an exact substring of the fetched abstract.