Osteosarcoma at the site of a previously treated simple bone cyst

Rarely sarcomas develop in previous bone cysts, especially in simple bone cysts. We present the first case report that an osteosarcoma developed at the site of a previous simple bone cyst that had been treated with curettage and bone-grafting without a history of radiation. The underlying mechanisms are still unclear, with the possibility of a second primary osteosarcoma at the same site or malignant transformation of the previous UBC. Overall, this is a very unusual patient with presentation of the two lesions, and the pathogenesis still needed to be clarified with more cases to be reported in the future.