Nobody knows why bone cancer develops. However, certain factors make it more likely; inclusive being a teenager or young adult(when bones are growing); exposure to radiotherapy (past treatment with radiotherapy); chemotherapy (depends on the type and dose of anti-cancer drugs used); Paget's disease (affects the bones, making them brittle and causing pain and fractures). A past benign bone tumour, non-spreading type increases likelihood to developing chondrosarcoma. Some inherited conditions like Li-Fraumeni syndrome and retinoblastoma puts you at a higher risk.
Attribution: BUPA