[Osteosarcoma manifesting as Paget's bone disease].

Osteosarcoma is a malignant bone tumour of mesenchymal osteoid tissue origin. Osteosarcoma can be primitive, but it may also complicated a Paget's disease of bone. We described a 75yearold man with a right thigh mass discovered after a motoring accident. Histopathologic examination revealed the diagnosis of osteosarcoma. Plain film Xrays showed Paget's lesion of the right pelvis bone. CT and MRI allowed complete evaluation of this lesion. Final diagnosis was those of malignant transformation of Paget disease. The patient was refused for surgery in view of the size of the tumour and chimiotherapy followed.