**Core Concept**
Retinoblastoma is a malignant tumor of the retina, primarily affecting children under the age of 5. It is a type of cancer that arises from the immature cells of the retina, which is the light-sensitive tissue at the back of the eye.

**Why the Correct Answer is Right**
Retinoblastoma is a hereditary tumor suppressor gene disorder, caused by mutations in the RB1 gene. This gene plays a crucial role in regulating cell growth and division. When the RB1 gene is mutated, it leads to uncontrolled cell growth, resulting in tumor formation. The disease can be inherited in an autosomal dominant pattern, meaning that a single copy of the mutated gene is sufficient to increase the risk of developing retinoblastoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Retinoblastoma is primarily a tumor of the optic nerve. Incorrect, as retinoblastoma is primarily a tumor of the retina, not the optic nerve.
**Option B:** Retinoblastoma is the most common type of eye cancer. Incorrect, as retinoblastoma is a rare form of eye cancer, accounting for only about 3% of all eye cancers.
**Option C:** Retinoblastoma can be treated with chemotherapy. Correct (not an option, but for reference), as chemotherapy is one of the treatment options for retinoblastoma.

**Clinical Pearl / High-Yield Fact**
Retinoblastoma is often associated with a characteristic "cat's eye" appearance on imaging studies, due to the presence of calcifications within the tumor.

**Correct Answer:** Not provided in the question. However, if you'd like me to explain any of the options A, B, or C, please provide them.