Hairy Cell Leukemia

MONDO:0018935 Pathograph 7 B-cell neoplasm

Hairy cell leukemia (HCL) is a rare indolent mature B-cell leukemia that is usually driven by a somatic BRAF V600E mutation and characterized by hairy-cell morphology, splenomegaly, monocytopenia, bone marrow involvement, and a characteristic immunophenotype with CD11c, CD25, CD103, and CD123 expression. This entry models the disease-level mechanism graph for classic HCL. Hairy cell leukemia variant and splenic diffuse red pulp small B-cell lymphoma are kept as differential diagnoses rather than subtype branches because they do not share the dominant BRAF-driven causal program of classic HCL.

0
Mappings
1
Definitions
0
Inheritance
6
Pathophysiology
1
Histopathology
5
Phenotypes
7
Pathograph
3
Genes
4
Treatments
1
Subtypes
3
Differentials
0
Datasets
0
Trials
0
Models
2
Literature
📘

Definitions

1
Diagnostic definition of classic hairy cell leukemia
Classic hairy cell leukemia is diagnosed by integrating hairy-cell morphology, the canonical HCL immunophenotypic score, marrow biopsy findings, and BRAF V600E testing.
DIAGNOSTIC_CRITERIA Adult classic hairy cell leukemia
Show evidence (1 reference)
PMID:34710243 SUPPORT Human Clinical
"Diagnosis of HCL is based on morphological evidence of hairy cells, an HCL immunologic score of 3 or 4 based on the CD11C, CD103, CD123, and CD25 expression, the trephine biopsy which makes it possible to specify the degree of tumoral medullary infiltration and the presence of BRAFV600E somatic mutation."
This review provides a compact disease-level diagnostic definition for classic hairy cell leukemia.
◆

Subtypes

1
Refractory Hairy Cell Leukemia MONDO:0004110
Flat treatment-response subtype capturing disease that is resistant to prior therapy. This is modeled as a response-state facet within the main HCL entry rather than as a separate disease-level mechanism page.
Show evidence (1 reference)
PMID:33979489 SUPPORT Human Clinical
"In a phase 2, single-center, academic trial involving patients with refractory or relapsed HCL, we assessed the safety and efficacy of vemurafenib (960 mg, administered twice daily for 8 weeks) plus concurrent and sequential rituximab."
This trial directly supports a clinically meaningful refractory/relapsed HCL state within the broader disease model.
📚

References

12
PMID:14991065
TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia.
No top-level findings curated for this source.
PMID:21663470
BRAF mutations in hairy-cell leukemia.
No top-level findings curated for this source.
PMID:23347903
Distinguishing hairy cell leukemia variant from hairy cell leukemia: development and validation of diagnostic criteria.
No top-level findings curated for this source.
PMID:27903528
Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia.
No top-level findings curated for this source.
PMID:28297625
Genomics of Hairy Cell Leukemia.
No top-level findings curated for this source.
PMID:30030507
Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia.
No top-level findings curated for this source.
PMID:32109194
Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia.
No top-level findings curated for this source.
PMID:33979489
Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia.
No top-level findings curated for this source.
PMID:34710243
Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment.
No top-level findings curated for this source.
PMID:35205796
Immunophenotypic Analysis of Hairy Cell Leukemia (HCL) and Hairy Cell Leukemia-like (HCL-like) Disorders.
No top-level findings curated for this source.
PMID:35454811
Deciphering Genetic Alterations of Hairy Cell Leukemia and Hairy Cell Leukemia-like Disorders in 98 Patients.
No top-level findings curated for this source.
PMID:38882583
Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach.
No top-level findings curated for this source.
⚙

Pathophysiology

6
BRAF V600E driver mutation
Classic HCL is defined by a clonal somatic BRAF V600E mutation that acts as the dominant upstream oncogenic lesion across nearly the entire disease course.
mature B cell link
Show evidence (2 references)
PMID:21663470 SUPPORT Human Clinical
"The BRAF V600E mutation was present in all patients with HCL who were evaluated."
This discovery study establishes BRAF V600E as the defining driver lesion of classic HCL.
PMID:28297625 SUPPORT Human Clinical
"Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the..."
This review reinforces that BRAF V600E is the dominant clonal lesion throughout classic HCL.
Constitutive RAF-MEK-ERK signaling
The oncogenic BRAF lesion drives persistent activation of the RAF-MEK-ERK cascade in classic HCL cells.
MAPK cascade link ↑ INCREASED
Show evidence (1 reference)
PMID:21663470 SUPPORT Human Clinical
"HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL."
This supports constitutive MAPK signaling as the core downstream biochemical consequence of BRAF V600E in HCL.
Apoptosis resistance of leukemic hairy cells
BRAF-driven signaling promotes an antiapoptotic state that helps malignant hairy cells persist within blood, marrow, and splenic compartments.
mature B cell link
apoptotic process link ↓ DECREASED
Show evidence (1 reference)
PMID:28297625 SUPPORT Human Clinical
"By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior."
This review directly links the canonical BRAF-MAPK program to apoptosis resistance in HCL cells.
TGF-beta1 overproduction by hairy cells
Hairy cells overproduce TGF-beta1 within marrow and splenic compartments, creating a local profibrotic cytokine environment.
mature B cell link
bone marrow link
Show evidence (1 reference)
PMID:14991065 SUPPORT Human Clinical
"RT-PCR and immunofluorescence studies showed that TGF-beta1 is overexpressed at the mRNA and protein levels in peripheral blood, spleen, and BM mononuclear cells and that hairy cells (HCs) are the main source of TGF-beta1."
This human-sample study supports hairy-cell-derived TGF-beta1 overproduction as a distinct upstream fibrogenic mechanism in HCL.
Bone marrow reticulin fibrosis
Marrow reticulin fibrosis is a characteristic stromal consequence of HCL and contributes to abnormal marrow architecture.
extracellular matrix organization link ↑ INCREASED
bone marrow link
Show evidence (1 reference)
PMID:14991065 SUPPORT Human Clinical
"Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP)."
This human-sample correlation supports marrow fibrosis as a core pathologic state tightly linked to hairy-cell burden.
Multilineage cytopenia from marrow failure
Classic HCL commonly manifests as multilineage cytopenia, especially pancytopenia, monocytopenia, neutropenia, and thrombocytopenia.
hemopoiesis link ↓ DECREASED
Show evidence (2 references)
PMID:27903528 SUPPORT Human Clinical
"Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection."
This guideline supports pancytopenia and infection susceptibility as central disease-level consequences of HCL.
PMID:38882583 SUPPORT Human Clinical
"In the basic blood count examination, leukopenia with monocytopenia and granulocytopenia, as well as aplastic anemia and/or thrombocytopenia occur."
This review specifies the characteristic multilineage cytopenia pattern seen in HCL.
✶

Histopathology

1
Bone marrow fibrosis FREQUENT
Bone marrow reticulin fibrosis is a characteristic biopsy finding in classic HCL and reflects hairy-cell-driven stromal remodeling.
Show evidence (1 reference)
PMID:14991065 SUPPORT Human Clinical
"Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP)."
This study supports bone marrow fibrosis as a characteristic histopathologic feature of HCL linked to hairy-cell infiltration.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Hairy Cell Leukemia Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

5
Blood 2
Pancytopenia VERY_FREQUENT Pancytopenia (HP:0001876)
Show evidence (1 reference)
PMID:27903528 SUPPORT Human Clinical
"Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection."
This guideline identifies pancytopenia as a defining phenotype of classic HCL.
Neutropenia VERY_FREQUENT Decreased total neutrophil count (HP:0001875)
Show evidence (1 reference)
PMID:38882583 SUPPORT Human Clinical
"The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
This review identifies neutropenia as a common manifestation of HCL.
Cardiovascular 1
Splenomegaly VERY_FREQUENT Splenomegaly (HP:0001744)
Show evidence (1 reference)
PMID:38882583 SUPPORT Human Clinical
"The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
This review explicitly identifies splenomegaly as one of the commonest clinical manifestations of HCL.
Immune 1
Recurrent infections FREQUENT Recurrent infections (HP:0002719)
Show evidence (1 reference)
PMID:27903528 SUPPORT Human Clinical
"The disease and its effective treatment are associated with immunosuppression."
This consensus guideline supports infection susceptibility as a disease-level consequence of HCL and its treatment.
Other 1
Monocytopenia VERY_FREQUENT Decreased total monocyte count (HP:0012312)
Show evidence (1 reference)
PMID:38882583 SUPPORT Human Clinical
"The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
This review identifies monocytopenia as a common and characteristic clinical feature of classic HCL.
🧬

Genetic Associations

3
BRAF V600E (Defining somatic driver)
Show evidence (1 reference)
PMID:21663470 SUPPORT Human Clinical
"The BRAF V600E mutation was present in all patients with HCL who were evaluated."
This study establishes BRAF V600E as the defining somatic driver of classic HCL.
KLF2 (Recurrent cooperating mutation)
Show evidence (1 reference)
PMID:28297625 SUPPORT Human Clinical
"Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis."
This review supports KLF2 as a recurrent cooperating genetic lesion in HCL.
CDKN1B (Recurrent cooperating mutation)
Show evidence (1 reference)
PMID:28297625 SUPPORT Human Clinical
"Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis."
This review supports CDKN1B as a recurrent cooperating lesion in HCL.
💊

Treatments

4
Purine nucleoside analog therapy
Action: pharmacotherapy MAXO:0000058
Agent: cladribine ↗ pentostatin ↗
Symptomatic first-line classic HCL is treated with purine nucleoside analogs, most commonly cladribine or pentostatin.
Show evidence (2 references)
PMID:34710243 SUPPORT Human Clinical
"Patients should be treated only if HCL is symptomatic. Chemotherapy with risk adapted therapy purine analogs (PNAs) are indicated in first-line HCL patients."
This review supports purine nucleoside analogs as first-line therapy for symptomatic classic HCL.
PMID:38882583 SUPPORT Human Clinical
"Currently, the main treatment for HCL involves the use of purine analogues, excluding pregnant women, individuals with severe infections, and those with relapsing HCL."
This review confirms purine analog therapy as the main treatment backbone for classic HCL.
Cladribine plus rituximab
Action: pharmacotherapy MAXO:0000058
Agent: cladribine ↗ rituximab ↗
Combining rituximab with first-line cladribine improves MRD-free complete remission depth and durability compared with cladribine alone.
Show evidence (1 reference)
PMID:32109194 SUPPORT Human Clinical
"At 96 months median follow-up, 94% versus 12% remained MRD free."
This randomized trial supports the durable MRD benefit of adding rituximab concurrently to first-line cladribine.
Vemurafenib plus rituximab
Action: pharmacotherapy MAXO:0000058
Agent: vemurafenib ↗ rituximab ↗
For relapsed or refractory classic HCL, combined BRAF inhibition and anti-CD20 therapy achieves high complete-response and MRD-negative response rates without myelotoxic chemotherapy.
Mechanism Target:
INHIBITS Constitutive RAF-MEK-ERK signaling — Vemurafenib targets the dominant BRAF V600E-driven MAPK program of classic HCL, while rituximab deepens cytoreduction.
Show evidence (1 reference)
PMID:33979489 SUPPORT Human Clinical
"Hairy-cell leukemia (HCL) is a CD20+ indolent B-cell cancer in which a BRAF V600E kinase-activating mutation plays a pathogenetic role."
This trial background statement supports BRAF-directed therapy as mechanism-matched treatment in classic HCL.
Show evidence (1 reference)
PMID:33979489 SUPPORT Human Clinical
"A complete response was observed in 26 patients (87%) in the intention-to-treat population."
This phase 2 study supports high activity of vemurafenib plus rituximab in relapsed/refractory classic HCL.
Moxetumomab pasudotox
Action: pharmacotherapy MAXO:0000058
Agent: Moxetumomab Pasudotox ↗
CD22-directed immunotoxin therapy is an active option for multiply pretreated relapsed or refractory HCL.
Show evidence (1 reference)
PMID:30030507 SUPPORT Human Clinical
"Among 80 patients (79% males; median age, 60.0 years), durable complete response (CR) rate was 30%, CR rate was 41%, and objective response rate (CR and partial response) was 75%; 64 patients (80%) achieved hematologic remission."
This pivotal study supports moxetumomab pasudotox as an active later-line therapy for relapsed/refractory HCL.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Hairy Cell Leukemia:

Hairy Cell Leukemia Variant Not Yet Curated MONDO:0017600
Overlapping Features HCL-v is an HCL-like mature B-cell leukemia that overlaps morphologically with classic HCL but does not share its canonical BRAF-driven immunophenotypic program or treatment sensitivity.
Distinguishing Features
  • HCL-v lacks CD25 and usually lacks or only dimly expresses CD123, unlike classic HCL.
  • HCL-v is typically BRAF V600E negative.
  • Prominent nucleoli are common in HCL-v but uncommon in classic HCL.
  • HCL-v is resistant to traditional HCL therapy.
Show evidence (1 reference)
PMID:23347903 SUPPORT Human Clinical
"HCL-v was negative for both annexin A1 (100%) and BRAFV600E mutation (100%), in contrast to HCL (74% positive for annexin A1; 76% positive for BRAFV600E mutation). HCL-v is resistant to traditional HCL therapy, making accurate diagnosis imperative."
This study directly supports the biologic and therapeutic separation between HCL-v and classic HCL.
Splenic Marginal Zone Lymphoma Not Yet Curated MONDO:0019462
Overlapping Features Splenic marginal zone lymphoma can resemble HCL in splenic and blood-based presentations but has a different immunophenotype and does not share the canonical BRAF-driven classic HCL program.
Distinguishing Features
  • SMZL is typically CD103 negative.
  • SMZL is usually CD123 negative, with only occasional dim expression.
  • SMZL lacks the classic HCL immunophenotypic score and BRAF-centered disease program.
Show evidence (1 reference)
PMID:23347903 SUPPORT Human Clinical
"SMZL cases were CD103(-) and CD123(-) except for one case with dim CD123."
This flow-cytometric study supports SMZL as a key diagnostic mimic distinguishable from HCL by its immunophenotype.
Splenic Diffuse Red Pulp Small B-cell Lymphoma Not Yet Curated MONDO:0017599
Overlapping Features SDRPL is an HCL-like splenic B-cell neoplasm with overlapping villous-cell morphology but a distinct phenotypic and genetic profile.
Distinguishing Features
  • SDRPL belongs to the HCL-like disorders rather than the classic HCL program.
  • HCL-like disorders such as SDRPL lack the full classic HCL marker pattern and diverge genetically from BRAF-driven HCL.
Show evidence (1 reference)
PMID:35205796 SUPPORT Human Clinical
"Hairy cell leukemia (HCL) is characterized by abnormal villous lymphoid cells that express CD103, CD123, CD25 and CD11c. HCL-like disorders, including hairy cell leukemia variant (vHCL) and splenic diffuse red pulp lymphoma (SDRPL), have similar morphologic criteria and a distinct phenotypic and..."
This study explicitly supports SDRPL as a differential diagnosis with morphologic overlap but a distinct program from classic HCL.
📚

Literature Summaries

2
Hairy Cell Leukemia Curator Notes ▸

Hairy Cell Leukemia Curator Notes

Modeling Choices

  • The dismech unit here is the disease-level mechanism graph for classic BRAF-driven HCL, anchored to MONDO:0018935.
  • HCL-v is not represented under has_subtypes because the literature consistently separates it from classic HCL by immunophenotype, BRAF status, and therapy response.
  • A flat response-state subtype is used for refractory HCL because that is a contextual disease-state facet, not a separate causal program.

MONDO And NCIT Roles

  • MONDO is used for the primary disease anchor, the refractory response-state subtype, and the differential diagnoses.
  • NCIT is used where the current schema supports oncology-specific grounding most naturally: histopathology (Bone Marrow Fibrosis), molecular diagnosis (BRAF V600E Mutation Analysis), and the antineoplastic agent Moxetumomab Pasudotox.
  • The current schema does not yet expose a disease-level NCIT mapping slot, and the current RegimenTerm dynamic enum did not accept the chosen HCL regimen codes during validation, so regimen specificity is carried by the treatment block plus ontology-grounded agents rather than forced into a failing pattern.

Graph Shape

  • The graph is kept atomic: driver mutation, MAPK activation, apoptosis resistance, TGF-beta1 overproduction, marrow fibrosis, and multilineage cytopenia are separate nodes.
  • Differential diagnosis carries HCL-v, SMZL, and SDRPL instead of creating placeholder pages for adjacent ontology classes.
OpenAI ▸
Hairy Cell Leukemia
gpt-5-codex

Hairy Cell Leukemia

Scope

  • This research package is scoped to the disease-level mechanism graph for classic hairy cell leukemia (HCL; MONDO:0018935).
  • Hairy cell leukemia variant (HCL-v) and splenic diffuse red pulp small B-cell lymphoma (SDRPL) are treated as differential diagnoses rather than subtype branches because the literature supports a distinct phenotypic and genetic program without the canonical BRAF-driven classic HCL mechanism (PMID:23347903, PMID:34710243, PMID:35205796).

Disease Overview

  • HCL is a rare indolent mature B-cell leukemia that represents about 2% of leukemias and predominantly affects older men (PMID:38882583).
  • The disease is defined diagnostically by hairy-cell morphology, a characteristic immunophenotype, marrow involvement, and near-universal BRAF V600E in classic HCL (PMID:21663470, PMID:34710243, PMID:38882583).

Diagnostic Signature

  • A practical diagnostic core is morphology plus the HCL score based on CD11c, CD25, CD103, and CD123, together with BRAF V600E testing (PMID:34710243).
  • Classic HCL typically expresses bright CD20, CD22, CD11c, CD25, CD103, and homogeneous CD123 (PMID:23347903).
  • HCL-v differs by loss of CD25, weak/absent CD123, absence of BRAF V600E, and relative resistance to traditional HCL therapy (PMID:23347903).

Core Mechanisms

  • BRAF V600E is the canonical driver lesion of classic HCL and is present clonally in almost all cases across the disease course (PMID:21663470, PMID:28297625).
  • BRAF V600E constitutively activates RAF-MEK-ERK signaling in HCL cells (PMID:21663470).
  • Review literature links this MAPK program to the characteristic hairy morphology and antiapoptotic behavior of HCL cells (PMID:28297625).
  • Hairy cells also overexpress TGF-beta1, which contributes directly to marrow reticulin fibrosis and correlates with marrow infiltration (PMID:14991065).
  • Bone marrow fibrosis and infiltration contribute to multilineage cytopenias, especially pancytopenia, monocytopenia, and neutropenia (PMID:14991065, PMID:27903528, PMID:38882583).

Histopathology And Phenotype

  • Bone marrow biopsy is important to assess the degree of medullary infiltration in HCL (PMID:34710243).
  • Reticulin fibrosis is a characteristic marrow abnormality mechanistically linked to hairy-cell-derived TGF-beta1 (PMID:14991065).
  • Common disease-level clinical manifestations include splenomegaly, pancytopenia, monocytopenia, neutropenia, and infection susceptibility (PMID:27903528, PMID:38882583).

Genetics Beyond BRAF

  • Recurrent cooperating lesions include KLF2 and CDKN1B alterations, but these are secondary to the canonical BRAF-driven disease program rather than replacing it (PMID:28297625, PMID:35454811).

Treatment Landscape

  • Symptomatic first-line HCL is treated with purine nucleoside analogs, classically cladribine or pentostatin (PMID:34710243, PMID:38882583).
  • Adding rituximab to first-line cladribine improves MRD-free complete remission durability (PMID:32109194).
  • Relapsed or refractory classic HCL is now strongly supported by BRAF-targeted therapy, particularly vemurafenib plus rituximab (PMID:33979489).
  • Moxetumomab pasudotox is an active CD22-directed option in multiply pretreated relapsed/refractory HCL (PMID:30030507).
  • BTK inhibition with ibrutinib appears in contemporary reviews as a later-line option, but the strongest curation-grade abstract evidence in this slice is for purine analogs, cladribine-rituximab, vemurafenib-rituximab, and moxetumomab pasudotox (PMID:34710243).
{ }

Source YAML

click to show 
name: Hairy Cell Leukemia
creation_date: '2026-04-12T00:00:00Z'
updated_date: '2026-04-12T00:00:00Z'
synonyms:
- HCL
- HCL-C
- classic hairy cell leukemia
- leukemic reticuloendotheliosis
description: >-
  Hairy cell leukemia (HCL) is a rare indolent mature B-cell leukemia that is
  usually driven by a somatic BRAF V600E mutation and characterized by hairy-cell
  morphology, splenomegaly, monocytopenia, bone marrow involvement, and a
  characteristic immunophenotype with CD11c, CD25, CD103, and CD123 expression.
  This entry models the disease-level mechanism graph for classic HCL. Hairy
  cell leukemia variant and splenic diffuse red pulp small B-cell lymphoma are
  kept as differential diagnoses rather than subtype branches because they do
  not share the dominant BRAF-driven causal program of classic HCL.
definitions:
- name: Diagnostic definition of classic hairy cell leukemia
  definition_type: DIAGNOSTIC_CRITERIA
  description: >-
    Classic hairy cell leukemia is diagnosed by integrating hairy-cell
    morphology, the canonical HCL immunophenotypic score, marrow biopsy
    findings, and BRAF V600E testing.
  scope: Adult classic hairy cell leukemia
  evidence:
  - reference: PMID:34710243
    reference_title: "Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnosis of HCL is based on morphological evidence of hairy cells, an HCL immunologic score of 3 or 4 based on the CD11C, CD103, CD123, and CD25 expression, the trephine biopsy which makes it possible to specify the degree of tumoral medullary infiltration and the presence of BRAFV600E somatic mutation."
    explanation: This review provides a compact disease-level diagnostic definition for classic hairy cell leukemia.
categories:
- Hematologic Malignancy
- B-cell Neoplasm
- Chronic Leukemia
- Lymphoproliferative Disorder
parents:
- B-cell neoplasm
has_subtypes:
- name: Refractory
  display_name: Refractory Hairy Cell Leukemia
  subtype_term:
    preferred_term: refractory hairy cell leukemia
    term:
      id: MONDO:0004110
      label: refractory hairy cell leukemia
  description: >-
    Flat treatment-response subtype capturing disease that is resistant to prior
    therapy. This is modeled as a response-state facet within the main HCL entry
    rather than as a separate disease-level mechanism page.
  evidence:
  - reference: PMID:33979489
    reference_title: "Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In a phase 2, single-center, academic trial involving patients with refractory or relapsed HCL, we assessed the safety and efficacy of vemurafenib (960 mg, administered twice daily for 8 weeks) plus concurrent and sequential rituximab."
    explanation: This trial directly supports a clinically meaningful refractory/relapsed HCL state within the broader disease model.
  review_notes: >-
    Added as a flat response-state facet per issue  # 1198 guidance. HCL-v was
    intentionally not placed under has_subtypes because it follows a distinct
    causal and therapeutic program.
prevalence:
- population: All leukemia cases
  percentage: 2
  evidence:
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia (HCL) represents 2% of all leukemia cases, with men aged above 55 years being the most affected."
    explanation: This review provides a disease-level frequency estimate and demographic summary for HCL.
epidemiology:
- name: Male-predominant disease of older adults
  description: >-
    Classic HCL most often affects older men, with typical presentation after
    age 55 years.
  evidence:
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia (HCL) represents 2% of all leukemia cases, with men aged above 55 years being the most affected."
    explanation: This review summarizes the characteristic demographic distribution of HCL.
disease_term:
  preferred_term: hairy cell leukemia
  term:
    id: MONDO:0018935
    label: hairy cell leukemia
pathophysiology:
- name: BRAF V600E driver mutation
  description: >-
    Classic HCL is defined by a clonal somatic BRAF V600E mutation that acts as
    the dominant upstream oncogenic lesion across nearly the entire disease
    course.
  cell_types:
  - preferred_term: mature B cell
    term:
      id: CL:0000785
      label: mature B cell
  evidence:
  - reference: PMID:21663470
    reference_title: "BRAF mutations in hairy-cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The BRAF V600E mutation was present in all patients with HCL who were evaluated."
    explanation: This discovery study establishes BRAF V600E as the defining driver lesion of classic HCL.
  - reference: PMID:28297625
    reference_title: "Genomics of Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the discovery of its underlying genetic cause, the BRAF-V600E kinase-activating mutation, which is somatically and clonally present in almost all patients through the entire disease spectrum and clinical course."
    explanation: This review reinforces that BRAF V600E is the dominant clonal lesion throughout classic HCL.
  downstream:
  - target: Constitutive RAF-MEK-ERK signaling
    description: The BRAF V600E lesion constitutively engages MAPK signaling in HCL cells.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:21663470
      reference_title: "BRAF mutations in hairy-cell leukemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL."
      explanation: This directly supports the edge from BRAF V600E to constitutive MAPK pathway activation.
- name: Constitutive RAF-MEK-ERK signaling
  description: >-
    The oncogenic BRAF lesion drives persistent activation of the RAF-MEK-ERK
    cascade in classic HCL cells.
  biological_processes:
  - preferred_term: MAPK cascade
    modifier: INCREASED
    term:
      id: GO:0000165
      label: MAPK cascade
  evidence:
  - reference: PMID:21663470
    reference_title: "BRAF mutations in hairy-cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL."
    explanation: This supports constitutive MAPK signaling as the core downstream biochemical consequence of BRAF V600E in HCL.
  downstream:
  - target: Apoptosis resistance of leukemic hairy cells
    description: Persistent MAPK signaling helps maintain the survival program of leukemic hairy cells.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - transcriptional reprogramming
    - survival signaling
    evidence:
    - reference: PMID:28297625
      reference_title: "Genomics of Hairy Cell Leukemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior."
      explanation: This review supports MAPK activation as an upstream driver of the antiapoptotic state of HCL cells.
- name: Apoptosis resistance of leukemic hairy cells
  description: >-
    BRAF-driven signaling promotes an antiapoptotic state that helps malignant
    hairy cells persist within blood, marrow, and splenic compartments.
  cell_types:
  - preferred_term: mature B cell
    term:
      id: CL:0000785
      label: mature B cell
  biological_processes:
  - preferred_term: apoptotic process
    modifier: DECREASED
    term:
      id: GO:0006915
      label: apoptotic process
  evidence:
  - reference: PMID:28297625
    reference_title: "Genomics of Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior."
    explanation: This review directly links the canonical BRAF-MAPK program to apoptosis resistance in HCL cells.
- name: TGF-beta1 overproduction by hairy cells
  description: >-
    Hairy cells overproduce TGF-beta1 within marrow and splenic compartments,
    creating a local profibrotic cytokine environment.
  locations:
  - preferred_term: bone marrow
    term:
      id: UBERON:0002371
      label: bone marrow
  cell_types:
  - preferred_term: mature B cell
    term:
      id: CL:0000785
      label: mature B cell
  evidence:
  - reference: PMID:14991065
    reference_title: "TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RT-PCR and immunofluorescence studies showed that TGF-beta1 is overexpressed at the mRNA and protein levels in peripheral blood, spleen, and BM mononuclear cells and that hairy cells (HCs) are the main source of TGF-beta1."
    explanation: This human-sample study supports hairy-cell-derived TGF-beta1 overproduction as a distinct upstream fibrogenic mechanism in HCL.
  downstream:
  - target: Bone marrow reticulin fibrosis
    description: Hairy-cell-derived TGF-beta1 drives fibrotic remodeling of the marrow stroma.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:14991065
      reference_title: "TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These results show, for the first time to our knowledge, that TGF-beta1 is highly expressed in HCs and is directly involved in the pathogenesis of BM reticulin fibrosis in HCL."
      explanation: This study directly supports the causal transition from TGF-beta1 overproduction to marrow reticulin fibrosis.
- name: Bone marrow reticulin fibrosis
  description: >-
    Marrow reticulin fibrosis is a characteristic stromal consequence of HCL and
    contributes to abnormal marrow architecture.
  locations:
  - preferred_term: bone marrow
    term:
      id: UBERON:0002371
      label: bone marrow
  biological_processes:
  - preferred_term: extracellular matrix organization
    modifier: INCREASED
    term:
      id: GO:0030198
      label: extracellular matrix organization
  evidence:
  - reference: PMID:14991065
    reference_title: "TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP)."
    explanation: This human-sample correlation supports marrow fibrosis as a core pathologic state tightly linked to hairy-cell burden.
  downstream:
  - target: Multilineage cytopenia from marrow failure
    description: Fibrotic and infiltrated marrow supports impaired production of multiple blood lineages.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - marrow architectural distortion
    - reduced hematopoietic reserve
    evidence:
    - reference: PMID:27903528
      reference_title: "Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection."
      explanation: This guideline-level statement supports marrow-failure consequences downstream of the characteristic marrow involvement of HCL.
- name: Multilineage cytopenia from marrow failure
  description: >-
    Classic HCL commonly manifests as multilineage cytopenia, especially
    pancytopenia, monocytopenia, neutropenia, and thrombocytopenia.
  biological_processes:
  - preferred_term: hemopoiesis
    modifier: DECREASED
    term:
      id: GO:0030097
      label: hemopoiesis
  evidence:
  - reference: PMID:27903528
    reference_title: "Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection."
    explanation: This guideline supports pancytopenia and infection susceptibility as central disease-level consequences of HCL.
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the basic blood count examination, leukopenia with monocytopenia and granulocytopenia, as well as aplastic anemia and/or thrombocytopenia occur."
    explanation: This review specifies the characteristic multilineage cytopenia pattern seen in HCL.
histopathology:
- name: Bone marrow fibrosis
  finding_term:
    preferred_term: Bone Marrow Fibrosis
    term:
      id: NCIT:C36212
      label: Bone Marrow Fibrosis
  frequency: FREQUENT
  diagnostic: true
  description: >-
    Bone marrow reticulin fibrosis is a characteristic biopsy finding in classic
    HCL and reflects hairy-cell-driven stromal remodeling.
  evidence:
  - reference: PMID:14991065
    reference_title: "TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP)."
    explanation: This study supports bone marrow fibrosis as a characteristic histopathologic feature of HCL linked to hairy-cell infiltration.
phenotypes:
- category: Abdominal
  name: Splenomegaly
  frequency: VERY_FREQUENT
  description: >-
    Splenic enlargement is a common presenting manifestation of classic HCL and
    reflects leukemic involvement of the spleen.
  phenotype_term:
    preferred_term: Splenomegaly
    term:
      id: HP:0001744
      label: Splenomegaly
  evidence:
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
    explanation: This review explicitly identifies splenomegaly as one of the commonest clinical manifestations of HCL.
- category: Hematologic
  name: Pancytopenia
  frequency: VERY_FREQUENT
  description: >-
    Reduction of all three blood-cell lineages is a core disease manifestation
    of HCL.
  phenotype_term:
    preferred_term: Pancytopenia
    term:
      id: HP:0001876
      label: Pancytopenia
  evidence:
  - reference: PMID:27903528
    reference_title: "Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection."
    explanation: This guideline identifies pancytopenia as a defining phenotype of classic HCL.
- category: Hematologic
  name: Monocytopenia
  frequency: VERY_FREQUENT
  diagnostic: true
  description: >-
    Monocytopenia is a characteristic hematologic abnormality of classic HCL and
    helps distinguish it from HCL-like disorders.
  phenotype_term:
    preferred_term: Decreased total monocyte count
    term:
      id: HP:0012312
      label: Decreased total monocyte count
  evidence:
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
    explanation: This review identifies monocytopenia as a common and characteristic clinical feature of classic HCL.
- category: Hematologic
  name: Neutropenia
  frequency: VERY_FREQUENT
  description: >-
    Neutropenia is common in HCL and contributes to infection risk.
  phenotype_term:
    preferred_term: Decreased total neutrophil count
    term:
      id: HP:0001875
      label: Decreased total neutrophil count
  evidence:
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common symptoms of this type of leukemia include splenomegaly, monocytopenia, and neutropenia."
    explanation: This review identifies neutropenia as a common manifestation of HCL.
- category: Infectious
  name: Recurrent infections
  frequency: FREQUENT
  description: >-
    Infection susceptibility reflects the combined effects of cytopenia and
    disease-associated immunosuppression.
  phenotype_term:
    preferred_term: Recurrent infections
    term:
      id: HP:0002719
      label: Recurrent infections
  evidence:
  - reference: PMID:27903528
    reference_title: "Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease and its effective treatment are associated with immunosuppression."
    explanation: This consensus guideline supports infection susceptibility as a disease-level consequence of HCL and its treatment.
diagnosis:
- name: Morphology and flow-cytometric immunophenotyping
  description: >-
    Diagnosis of classic HCL is established by hairy-cell morphology together
    with the canonical immunophenotypic pattern based on CD11c, CD25, CD103,
    and CD123.
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: MAXO:0000003
      label: diagnostic procedure
  markers: CD11c, CD25, CD103, CD123
  evidence:
  - reference: PMID:34710243
    reference_title: "Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnosis of HCL is based on morphological evidence of hairy cells, an HCL immunologic score of 3 or 4 based on the CD11C, CD103, CD123, and CD25 expression, the trephine biopsy which makes it possible to specify the degree of tumoral medullary infiltration and the presence of BRAFV600E somatic mutation."
    explanation: This review supports morphology plus the characteristic immunophenotypic score as the core diagnostic approach for classic HCL.
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Immunophenotypic analysis of the HCL cells reveals high expression of B-lineage antigens, including CD19, CD20, and CD22. Additionally, CD11c, CD25, CD103, and CD123 belong to specific markers of HCL."
    explanation: This review reinforces the canonical immunophenotypic signature of classic HCL.
- name: Molecular testing for BRAF V600E
  description: >-
    Detection of BRAF V600E is highly supportive of classic HCL and helps
    distinguish it from HCL-like disorders.
  diagnosis_term:
    preferred_term: BRAF V600E Mutation Analysis
    term:
      id: NCIT:C80273
      label: BRAF V600E Mutation Analysis
  markers: BRAF V600E
  evidence:
  - reference: PMID:21663470
    reference_title: "BRAF mutations in hairy-cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The BRAF V600E mutation was present in all patients with HCL who were evaluated."
    explanation: This discovery study supports BRAF V600E testing as a defining molecular diagnostic assay for classic HCL.
  - reference: PMID:28297625
    reference_title: "Genomics of Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus, testing for BRAF-V600E allows for a genetics-based differential diagnosis between HCL and HCL-like tumors, even noninvasively in routine blood samples."
    explanation: This review explicitly supports BRAF V600E testing for differential diagnosis between classic HCL and its mimics.
differential_diagnoses:
- name: Hairy Cell Leukemia Variant
  disease_term:
    preferred_term: hairy cell leukemia variant
    term:
      id: MONDO:0017600
      label: hairy cell leukemia variant
  description: >-
    HCL-v is an HCL-like mature B-cell leukemia that overlaps morphologically
    with classic HCL but does not share its canonical BRAF-driven immunophenotypic
    program or treatment sensitivity.
  distinguishing_features:
  - HCL-v lacks CD25 and usually lacks or only dimly expresses CD123, unlike classic HCL.
  - HCL-v is typically BRAF V600E negative.
  - Prominent nucleoli are common in HCL-v but uncommon in classic HCL.
  - HCL-v is resistant to traditional HCL therapy.
  evidence:
  - reference: PMID:23347903
    reference_title: "Distinguishing hairy cell leukemia variant from hairy cell leukemia: development and validation of diagnostic criteria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HCL-v was negative for both annexin A1 (100%) and BRAFV600E mutation (100%), in contrast to HCL (74% positive for annexin A1; 76% positive for BRAFV600E mutation). HCL-v is resistant to traditional HCL therapy, making accurate diagnosis imperative."
    explanation: This study directly supports the biologic and therapeutic separation between HCL-v and classic HCL.
- name: Splenic Marginal Zone Lymphoma
  disease_term:
    preferred_term: splenic marginal zone lymphoma
    term:
      id: MONDO:0019462
      label: splenic marginal zone lymphoma
  description: >-
    Splenic marginal zone lymphoma can resemble HCL in splenic and blood-based
    presentations but has a different immunophenotype and does not share the
    canonical BRAF-driven classic HCL program.
  distinguishing_features:
  - SMZL is typically CD103 negative.
  - SMZL is usually CD123 negative, with only occasional dim expression.
  - SMZL lacks the classic HCL immunophenotypic score and BRAF-centered disease program.
  evidence:
  - reference: PMID:23347903
    reference_title: "Distinguishing hairy cell leukemia variant from hairy cell leukemia: development and validation of diagnostic criteria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SMZL cases were CD103(-) and CD123(-) except for one case with dim CD123."
    explanation: This flow-cytometric study supports SMZL as a key diagnostic mimic distinguishable from HCL by its immunophenotype.
- name: Splenic Diffuse Red Pulp Small B-cell Lymphoma
  disease_term:
    preferred_term: splenic diffuse red pulp small B-cell lymphoma
    term:
      id: MONDO:0017599
      label: splenic diffuse red pulp small B-cell lymphoma
  description: >-
    SDRPL is an HCL-like splenic B-cell neoplasm with overlapping villous-cell
    morphology but a distinct phenotypic and genetic profile.
  distinguishing_features:
  - SDRPL belongs to the HCL-like disorders rather than the classic HCL program.
  - HCL-like disorders such as SDRPL lack the full classic HCL marker pattern and diverge genetically from BRAF-driven HCL.
  evidence:
  - reference: PMID:35205796
    reference_title: "Immunophenotypic Analysis of Hairy Cell Leukemia (HCL) and Hairy Cell Leukemia-like (HCL-like) Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hairy cell leukemia (HCL) is characterized by abnormal villous lymphoid cells that express CD103, CD123, CD25 and CD11c. HCL-like disorders, including hairy cell leukemia variant (vHCL) and splenic diffuse red pulp lymphoma (SDRPL), have similar morphologic criteria and a distinct phenotypic and genetic profile."
    explanation: This study explicitly supports SDRPL as a differential diagnosis with morphologic overlap but a distinct program from classic HCL.
genetic:
- name: BRAF V600E
  gene_term:
    preferred_term: BRAF
    term:
      id: hgnc:1097
      label: B-Raf proto-oncogene, serine/threonine kinase
  association: Defining somatic driver
  frequency: VERY_FREQUENT
  notes: >-
    Canonical kinase-activating driver lesion of classic HCL. Useful both for
    diagnosis and for targeted therapy selection. Usually absent in HCL-v and
    other HCL-like disorders.
  evidence:
  - reference: PMID:21663470
    reference_title: "BRAF mutations in hairy-cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The BRAF V600E mutation was present in all patients with HCL who were evaluated."
    explanation: This study establishes BRAF V600E as the defining somatic driver of classic HCL.
- name: KLF2
  gene_term:
    preferred_term: KLF2
    term:
      id: hgnc:6347
      label: KLF transcription factor 2
  association: Recurrent cooperating mutation
  notes: >-
    Recurrent but secondary lesion in a minority of classic HCL cases that may
    cooperate with the dominant BRAF-driven program.
  evidence:
  - reference: PMID:28297625
    reference_title: "Genomics of Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis."
    explanation: This review supports KLF2 as a recurrent cooperating genetic lesion in HCL.
- name: CDKN1B
  gene_term:
    preferred_term: CDKN1B
    term:
      id: hgnc:1785
      label: cyclin dependent kinase inhibitor 1B
  association: Recurrent cooperating mutation
  notes: >-
    Secondary recurrent lesion in classic HCL that likely modifies the
    BRAF-driven disease program rather than replacing it.
  evidence:
  - reference: PMID:28297625
    reference_title: "Genomics of Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis."
    explanation: This review supports CDKN1B as a recurrent cooperating lesion in HCL.
treatments:
- name: Purine nucleoside analog therapy
  description: >-
    Symptomatic first-line classic HCL is treated with purine nucleoside
    analogs, most commonly cladribine or pentostatin.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: cladribine
      term:
        id: CHEBI:567361
        label: cladribine
    - preferred_term: pentostatin
      term:
        id: CHEBI:27834
        label: pentostatin
  evidence:
  - reference: PMID:34710243
    reference_title: "Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients should be treated only if HCL is symptomatic. Chemotherapy with risk adapted therapy purine analogs (PNAs) are indicated in first-line HCL patients."
    explanation: This review supports purine nucleoside analogs as first-line therapy for symptomatic classic HCL.
  - reference: PMID:38882583
    reference_title: "Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Currently, the main treatment for HCL involves the use of purine analogues, excluding pregnant women, individuals with severe infections, and those with relapsing HCL."
    explanation: This review confirms purine analog therapy as the main treatment backbone for classic HCL.
- name: Cladribine plus rituximab
  description: >-
    Combining rituximab with first-line cladribine improves MRD-free complete
    remission depth and durability compared with cladribine alone.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: cladribine
      term:
        id: CHEBI:567361
        label: cladribine
    - preferred_term: rituximab
      term:
        id: CHEBI:64357
        label: rituximab
  evidence:
  - reference: PMID:32109194
    reference_title: "Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 96 months median follow-up, 94% versus 12% remained MRD free."
    explanation: This randomized trial supports the durable MRD benefit of adding rituximab concurrently to first-line cladribine.
- name: Vemurafenib plus rituximab
  description: >-
    For relapsed or refractory classic HCL, combined BRAF inhibition and
    anti-CD20 therapy achieves high complete-response and MRD-negative response
    rates without myelotoxic chemotherapy.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: vemurafenib
      term:
        id: CHEBI:63637
        label: vemurafenib
    - preferred_term: rituximab
      term:
        id: CHEBI:64357
        label: rituximab
  target_mechanisms:
  - target: Constitutive RAF-MEK-ERK signaling
    treatment_effect: INHIBITS
    description: >-
      Vemurafenib targets the dominant BRAF V600E-driven MAPK program of classic
      HCL, while rituximab deepens cytoreduction.
    evidence:
    - reference: PMID:33979489
      reference_title: "Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Hairy-cell leukemia (HCL) is a CD20+ indolent B-cell cancer in which a BRAF V600E kinase-activating mutation plays a pathogenetic role."
      explanation: This trial background statement supports BRAF-directed therapy as mechanism-matched treatment in classic HCL.
  evidence:
  - reference: PMID:33979489
    reference_title: "Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A complete response was observed in 26 patients (87%) in the intention-to-treat population."
    explanation: This phase 2 study supports high activity of vemurafenib plus rituximab in relapsed/refractory classic HCL.
- name: Moxetumomab pasudotox
  description: >-
    CD22-directed immunotoxin therapy is an active option for multiply
    pretreated relapsed or refractory HCL.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: Moxetumomab Pasudotox
      term:
        id: NCIT:C68819
        label: Moxetumomab Pasudotox
  evidence:
  - reference: PMID:30030507
    reference_title: "Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among 80 patients (79% males; median age, 60.0 years), durable complete response (CR) rate was 30%, CR rate was 41%, and objective response rate (CR and partial response) was 75%; 64 patients (80%) achieved hematologic remission."
    explanation: This pivotal study supports moxetumomab pasudotox as an active later-line therapy for relapsed/refractory HCL.
review_notes: >-
  Applied issue  # 1198 cancer curation guidance by keeping one disease-level
  mechanism graph for classic HCL, anchoring the disease MONDO-first, using a
  flat refractory response-state subtype, and treating HCL-v/SMZL/SDRPL as
  differential diagnoses rather than subtype branches. NCIT was used where the
  schema supports oncology-specific grounding best, especially histopathology
  and regimen-level treatment modeling.
references:
- reference: PMID:14991065
  title: TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:21663470
  title: BRAF mutations in hairy-cell leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:23347903
  title: "Distinguishing hairy cell leukemia variant from hairy cell leukemia: development and validation of diagnostic criteria."
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:27903528
  title: Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:28297625
  title: Genomics of Hairy Cell Leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:30030507
  title: Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:32109194
  title: Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:33979489
  title: Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:34710243
  title: "Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment."
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:35205796
  title: Immunophenotypic Analysis of Hairy Cell Leukemia (HCL) and Hairy Cell Leukemia-like (HCL-like) Disorders.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:35454811
  title: Deciphering Genetic Alterations of Hairy Cell Leukemia and Hairy Cell Leukemia-like Disorders in 98 Patients.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []
- reference: PMID:38882583
  title: Hairy cell leukemia - etiopathogenesis, diagnosis and modern therapeutic approach.
  found_in:
  - Hairy_Cell_Leukemia-deep-research-openai.md
  findings: []