**Core Concept**
Retinoblastoma is a malignant tumor of the retina, primarily affecting children, and is associated with mutations in the RB1 gene. This genetic alteration leads to uncontrolled cell proliferation and tumor formation.

**Why the Correct Answer is Right**
The RB1 gene acts as a tumor suppressor, regulating the cell cycle by binding to and inhibiting the E2F transcription factor. When the RB1 gene is mutated, it fails to perform its normal function, resulting in uncontrolled cell growth and tumor formation. The RB1 gene is located on the long arm of chromosome 13 (13q14).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because retinoblastoma is indeed characterized by mutations in the RB1 gene, which is a well-established fact.
**Option B:** This option is incorrect because retinoblastoma is primarily a disease of childhood, with the majority of cases presenting before the age of 5.
**Option C:** This option is incorrect because retinoblastoma is a malignant tumor, and its primary treatment involves a combination of chemotherapy, radiation therapy, and surgery.

**Clinical Pearl / High-Yield Fact**
Retinoblastoma is a classic example of a "two-hit" hypothesis, where a mutation in one allele of the RB1 gene is sufficient to initiate tumor formation, and a second mutation in the remaining allele is required for full malignant transformation.

**Correct Answer: B. Retinoblastoma primarily affects children.**