Retinoblastoma is a rare pediatric malignancy arising from the nuclear layer of the retina, representing the paradigmatic example of the two-hit hypothesis of tumor suppressor gene inactivation. Biallelic loss of RB1 function is required for tumorigenesis. In hereditary cases (40%), a germline RB1 mutation is inherited and a somatic second hit occurs, leading to bilateral/multifocal tumors and increased risk of secondary malignancies. In sporadic cases (60%), both RB1 alleles are inactivated somatically in a single retinal cell.
graph LR
Loss_of_Cell_Cycle_Checkpoint_Control["Loss of Cell Cycle Checkpoint Control"]
Uncontrolled_Retinal_Cell_Proliferation["Uncontrolled Retinal Cell Proliferation"]
RB1_Tumor_Suppressor_Inactivation["RB1 Tumor Suppressor Inactivation"]
RB1_Tumor_Suppressor_Inactivation --> Loss_of_Cell_Cycle_Checkpoint_Control
Loss_of_Cell_Cycle_Checkpoint_Control --> Uncontrolled_Retinal_Cell_Proliferation
style Loss_of_Cell_Cycle_Checkpoint_Control fill:#dbeafe
style Uncontrolled_Retinal_Cell_Proliferation fill:#dbeafe
style RB1_Tumor_Suppressor_Inactivation fill:#dbeafe
name: Retinoblastoma
creation_date: '2026-01-26T02:55:13Z'
updated_date: '2026-02-16T20:19:38Z'
description: >-
Retinoblastoma is a rare pediatric malignancy arising from the nuclear layer of
the retina, representing the paradigmatic example of the two-hit hypothesis of
tumor suppressor gene inactivation. Biallelic loss of RB1 function is required
for tumorigenesis. In hereditary cases (40%), a germline RB1 mutation is inherited
and a somatic second hit occurs, leading to bilateral/multifocal tumors and
increased risk of secondary malignancies. In sporadic cases (60%), both RB1
alleles are inactivated somatically in a single retinal cell.
categories:
- Pediatric Cancer
- Ocular Malignancy
- Hereditary Cancer Syndrome
parents:
- retinal cancer
has_subtypes:
- name: Hereditary Retinoblastoma
description: >-
Caused by germline RB1 mutation (first hit) present in all cells, with somatic
loss of the remaining allele in retinal cells. Typically bilateral or multifocal.
Patients have 50% chance of passing mutation to offspring and increased lifetime
risk of secondary malignancies including osteosarcoma.
evidence:
- reference: PMID:5279523
supports: SUPPORT
snippet: "In the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells."
explanation: Knudson's analysis established that hereditary retinoblastoma involves germline inheritance of the first mutation.
- name: Sporadic Retinoblastoma
description: >-
Both RB1 alleles are inactivated by somatic mutations in a single retinal
precursor cell. Typically unilateral and unifocal. No increased risk of
secondary malignancies and no familial transmission unless mosaicism present.
evidence:
- reference: PMID:5279523
supports: SUPPORT
snippet: "In the nonhereditary form, both mutations occur in somatic cells."
explanation: Knudson established that sporadic retinoblastoma requires two somatic mutations in the same cell.
pathophysiology:
- name: RB1 Tumor Suppressor Inactivation
description: >-
The RB1 gene encodes the retinoblastoma protein (pRB), a critical regulator of
the cell cycle. Biallelic RB1 loss removes the constraint on E2F transcription
factors, allowing uncontrolled progression through the G1/S checkpoint.
Retinoblastoma exemplifies Knudson's two-hit hypothesis: in hereditary cases,
one mutation is inherited and the second is somatic; in sporadic cases, both
mutations occur somatically in the same cell.
cell_types:
- preferred_term: retinal progenitor cell
term:
id: CL:0002672
label: retinal progenitor cell
biological_processes:
- preferred_term: G1/S transition of mitotic cell cycle
modifier: ABNORMAL
term:
id: GO:0000082
label: G1/S transition of mitotic cell cycle
locations:
- preferred_term: retina
term:
id: UBERON:0000966
label: retina
downstream:
- target: Loss of Cell Cycle Checkpoint Control
description: pRB loss releases E2F transcription factors from inhibition
- name: Loss of Cell Cycle Checkpoint Control
description: >-
pRB normally binds and inhibits E2F transcription factors during G1 phase.
When pRB is phosphorylated by cyclin-dependent kinases or functionally lost,
E2F is released to activate genes required for S-phase entry, including
cyclins, DNA replication factors, and proliferative genes.
biological_processes:
- preferred_term: cell cycle checkpoint signaling
modifier: DECREASED
term:
id: GO:0000075
label: cell cycle checkpoint signaling
- preferred_term: positive regulation of transcription by RNA polymerase II
modifier: INCREASED
term:
id: GO:0045944
label: positive regulation of transcription by RNA polymerase II
downstream:
- target: Uncontrolled Retinal Cell Proliferation
description: E2F-driven gene expression promotes S-phase entry and cell division
- name: Uncontrolled Retinal Cell Proliferation
description: >-
Loss of pRB-mediated cell cycle control results in constitutive E2F activity,
driving retinal progenitor cells through repeated rounds of DNA replication
and cell division. This uncontrolled proliferation leads to tumor formation.
cell_types:
- preferred_term: retinal progenitor cell
term:
id: CL:0002672
label: retinal progenitor cell
biological_processes:
- preferred_term: cell population proliferation
modifier: INCREASED
term:
id: GO:0008283
label: cell population proliferation
evidence:
- reference: PMID:5279523
supports: PARTIAL
snippet: "retinoblastoma is a cancer caused by two mutational events. In the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells."
explanation: This is the foundational Knudson paper establishing the two-hit hypothesis based on statistical analysis of retinoblastoma cases.
histopathology:
- name: Intraocular Malignancy
finding_term:
preferred_term: Retinoblastoma
term:
id: NCIT:C7541
label: Retinoblastoma
frequency: VERY_FREQUENT
description: Retinoblastoma is the most common intraocular malignancy.
evidence:
- reference: PMID:41567907
supports: SUPPORT
snippet: "Retinoblastoma is the most common intraocular malignancy in"
explanation: Abstract notes retinoblastoma is the most common intraocular malignancy.
phenotypes:
- category: Ocular
name: Leukocoria
frequency: VERY_FREQUENT
diagnostic: true
description: >-
White pupillary reflex (cat's eye reflex) is the most common presenting sign,
resulting from light reflecting off the tumor surface. Often noticed in
photographs or by parents.
phenotype_term:
preferred_term: Leukocoria
term:
id: HP:0000555
label: Leukocoria
- category: Ocular
name: Strabismus
frequency: FREQUENT
diagnostic: true
description: >-
Misalignment of the eyes is the second most common presenting sign, occurring
when the tumor affects macular vision and disrupts binocular fusion.
phenotype_term:
preferred_term: Strabismus
term:
id: HP:0000486
label: Strabismus
- category: Ocular
name: Decreased Visual Acuity
frequency: FREQUENT
description: >-
Vision loss occurs when the tumor involves the macula or becomes large enough
to obstruct the visual axis.
phenotype_term:
preferred_term: Decreased visual acuity
term:
id: HP:0007663
label: Reduced visual acuity
- category: Ocular
name: Ocular Pain
frequency: OCCASIONAL
description: >-
Eye pain may occur with advanced disease causing secondary glaucoma or
inflammation.
phenotype_term:
preferred_term: Eye pain
term:
id: HP:0200026
label: Ocular pain
- category: Systemic
name: Secondary Malignancies
frequency: OCCASIONAL
description: >-
Patients with hereditary retinoblastoma have significantly increased risk of
secondary cancers, particularly osteosarcoma, soft tissue sarcomas, and
melanoma. Risk is increased further by external beam radiation therapy.
phenotype_term:
preferred_term: Neoplasm
term:
id: HP:0002664
label: Neoplasm
biochemical:
- name: RB1 Genetic Testing
notes: >-
Molecular testing identifies RB1 mutations including point mutations, small
insertions/deletions, large deletions, and promoter hypermethylation. Testing
is essential for genetic counseling and surveillance of family members.
genetic:
- name: RB1
association: Germline and Somatic Mutations
inheritance:
- name: Autosomal Dominant
notes: >-
RB1 (13q14.2) encodes the retinoblastoma protein, the first tumor suppressor
gene identified. Loss-of-function mutations include nonsense, frameshift, splice
site, and large deletions. Germline mutations are present in 40% of cases.
Hereditary retinoblastoma follows autosomal dominant inheritance with high
but incomplete penetrance (approximately 90%).
treatments:
- name: Focal Therapy (Laser/Cryotherapy)
description: >-
Small tumors may be treated with focal ablation including laser photocoagulation
or cryotherapy. These treatments spare vision and avoid systemic toxicity.
treatment_term:
preferred_term: laser ablation therapy
term:
id: MAXO:0000453
label: laser ablation therapy
- name: Chemotherapy
description: >-
Systemic chemotherapy with carboplatin, vincristine, and etoposide (CEV) reduces
tumor size enabling focal consolidation. Intra-arterial chemotherapy delivers
melphalan directly to the ophthalmic artery for localized effect.
treatment_term:
preferred_term: chemotherapy
term:
id: MAXO:0000647
label: chemotherapy
therapeutic_agent:
- preferred_term: carboplatin
term:
id: CHEBI:31355
label: carboplatin
- preferred_term: vincristine
term:
id: CHEBI:27375
label: vincristine
- preferred_term: etoposide
term:
id: CHEBI:4911
label: etoposide
- preferred_term: melphalan
term:
id: CHEBI:28876
label: melphalan
- name: Enucleation
description: >-
Surgical removal of the eye is indicated for advanced intraocular disease,
particularly when vision cannot be preserved. Provides excellent local control
and prevents extraocular spread.
treatment_term:
preferred_term: surgical procedure
term:
id: MAXO:0000004
label: surgical procedure
- name: External Beam Radiation
description: >-
Historically used for retinoblastoma but now avoided when possible due to
significantly increased risk of secondary malignancies in RB1 germline
mutation carriers, particularly osteosarcoma in the radiation field.
treatment_term:
preferred_term: radiation therapy
term:
id: MAXO:0000014
label: radiation therapy
disease_term:
preferred_term: retinoblastoma
term:
id: MONDO:0008380
label: retinoblastoma
classifications:
icdo_morphology:
classification_value: Embryonal Neoplasm
harrisons_chapter:
- classification_value: cancer
- classification_value: solid tumor