This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
A patient with known mutation in the `RB gene' is `disease free' from Retinoblastoma. The patient is at highest risk of developing which of the following malignancies – 
Select and explain. 
A. Renal cell carcinoma, B. Osteosarcoma, C. Pinealoblastoma, D. Chondrosarcoma
B: Osteosarcoma
Answer: B: Osteosarcoma 
Explanation: Most common secondary tumor in survivors of retinoblastoma is osteosarcoma.