A patient with known mutation in the 'Rb gene' is 'disease free' from Retinoblastoma. This patient is at highest risk of developing which of the following malignancies?

Retinoblastoma gene locus resides on human chromosome 13 at band q14, it functions by blocking the entry of cells into the DNA synthesis S phase of the cell cycle. It is a prototype tumor suppressor gene in which a loss of both normal alleles is associated with tumor development. Mutation in Rb gene is associated with the development of retinoblastoma, osteosarcoma, soft tissue sarcoma, fibrosarcoma, neuroblastoma and meningioma. Osteosarcoma of the skull occur 2000 times more frequently in survivors of retinoblastoma than in general population. Osteosarcoma is the most common tumor outside the radiation field. Since the patient in the question does not have retinoblastoma he is at very high risk of developing osteosarcoma. Ref: Oski's Essential Pediatrics By Michael Crocett, 2nd Edition, Pages 484-5