Multicentric osteosarcoma.

Multicentric osteosarcoma is a rare type of osteosarcoma with a poor prognosis. It is usually described as the occurrence of tumorous lesions in more than one bone, but without pulmonary metastasis. It may be of a synchronous or metachronous variety. We report the case of a 12-year-old boy with a synchronous variety of multicentric osteosarcoma, although he did not have any risk factors for the disease. We also discuss the current debate on whether multicentric osteosarcoma represents multiple primary tumours or metastatic disease.