**Core Concept**
The retinoblastoma (Rb) gene is a tumor suppressor gene that plays a crucial role in regulating the cell cycle, particularly in the G1 phase. Deletion or mutation of the Rb gene leads to uncontrolled cell proliferation and cancer development.

**Why the Correct Answer is Right**
Deletion of both copies of the Rb gene in the same developing cell, also known as biallelic inactivation, is a hallmark of retinoblastoma, a rare form of eye cancer that typically affects children. This deletion disrupts the Rb protein's ability to bind to and inhibit the E2F transcription factor, leading to unchecked cell growth and tumor formation.

**Why Each Wrong Option is Incorrect**
**Option A:** Li-Fraumeni syndrome is associated with mutations in the TP53 gene, not the Rb gene.
**Option B:** Neurofibromatosis type 1 is caused by mutations in the NF1 gene and is characterized by multiple non-cancerous tumors, not retinoblastoma.
**Option C:** Familial adenomatous polyposis (FAP) is linked to mutations in the APC gene and is associated with colorectal cancer, not retinoblastoma.

**Clinical Pearl / High-Yield Fact**
The Rb gene is a classic example of a tumor suppressor gene, and its inactivation is a key step in the development of retinoblastoma. Remember that biallelic inactivation of the Rb gene is a critical event in the pathogenesis of this cancer.

**Correct Answer:** C. Retinoblastoma