**Question:** True about retinoblastoma are all except:

A. It is a genetic disorder caused by mutations in the RB1 gene.
B. It primarily affects children under the age of 5.
C. The tumor is exclusively located in the retina and does not involve other tissues or organs.
D. The disease is exclusively caused by radiation exposure.

**Core Concept:**
Retinoblastoma is a rare genetic cancer that primarily affects young children. It is a result of mutations in the RB1 gene, which is responsible for regulating cell growth and division. In this case, the mutations lead to uncontrolled cell growth and formation of tumors, specifically in the retina. Retinoblastoma is classified as an **ocular malignancy**.

**Why the Correct Answer is Right:**
Option D is incorrect because retinoblastoma is not exclusively caused by radiation exposure. It is a genetically inherited disorder resulting from mutations in the RB1 gene. While radiation exposure is a risk factor, it is not the sole cause of retinoblastoma.

Option C is incorrect because retinoblastoma can involve not only the retina but also the vitreous humor, optic nerve, and sometimes other tissues, including the brain. Although the tumor primarily originates in the retina, the disease can spread to other parts of the body.

Option A is correct, as retinoblastoma is a genetic disorder caused by mutations in the RB1 gene, which is responsible for regulating cell growth and division. While the presence of the mutation indicates a family history of retinoblastoma, radiation exposure, or inherited mutations can lead to the disease. However, the statement is not entirely false, as mutations can occur due to unknown causes or sporadic cases.

Option B is correct because retinoblastoma is a rare disease that primarily affects children under the age of 5. It is not limited to a specific age group or only occurring in adults.

**Why Each Wrong Option is Incorrect:**

- Option D (retinoblastoma caused by radiation exposure) is incorrect because it is a genetic disorder primarily caused by mutations in the RB1 gene. Radiation exposure is a risk factor, not the sole cause.
- Option C (retinoblastoma is a single-organ disease) is incorrect because the tumor can spread to other parts of the body. Although the disease primarily affects the retina, it might involve other tissues like the optic nerve and vitreous humor.
- Option A (retinoblastoma is a non-hereditary disease) is incorrect because it is a genetic disorder caused by mutations in the RB1 gene. However, the presence of the mutation indicates a family history of retinoblastoma, which could be due to inherited mutations or unknown causes (sporadic cases).
- Option B (retinoblastoma is a disease of adults) is incorrect because retinoblastoma primarily affects children under the age of 5 years. Although it is rare, this disease can occur in adults as well.

**Clinical Pearls:**
Retinoblastoma is an extremely rare cancer of the embryonic retina that can lead to vision loss or blindness if left untreated. The RB1 gene mutation is the primary cause of retinoblastoma. Inheritance can occur