**Core Concept**
Osteosarcoma is a primary malignant bone tumor arising from osteoblasts, most commonly in adolescents and young adults. While it is not directly linked to retinoblastoma, both are associated with germline mutations in the *RB1* gene, making them part of a broader spectrum of retinoblastoma-associated tumors.

**Why the Correct Answer is Right**
Retinoblastoma is strongly associated with germline mutations in the *RB1* gene, which predisposes individuals to multiple cancers, including osteosarcoma. Patients with hereditary retinoblastoma have a significantly increased risk of developing osteosarcoma, especially in the long bones, due to loss of cell cycle control from *RB1* dysfunction. This association is well-documented in familial retinoblastoma cases and is a classic example of a tumor predisposition syndrome.

**Why Each Wrong Option is Incorrect**
Option A: Wilms tumor is a renal tumor arising from metanephric mesenchyme and is associated with *WT1* gene mutations, not *RB1*. It does not link to osteosarcoma.
Option C: Rhabdomyosarcoma arises from mesenchymal cells and is more common in children, with association to *PAX3/FOXO1* fusions, not *RB1*.
Option D: Ewing tumor is a small round blue cell tumor linked to *EWSR1* rearrangements, not *RB1* mutations, and has no strong association with osteosarcoma.

**Clinical Pearl / High-Yield Fact**
Patients with hereditary retinoblastoma have a 40–50% lifetime risk of developing osteosarcoma, making *RB1* gene testing crucial in such cases. This is a key diagnostic clue in pediatric oncology.

✓ Correct Answer: B. Retinoblastoma