Metachronous multifocal osteosarcoma: a case report and literature review.

Metachronous multifocal osteosarcoma (MFOS) is a rare form of osteosarcoma manifested by one or more new tumors developing after the initial treatment of primary osteosarcoma. The pathogenesis of metachronous MFOS is still obscure whether it represents multiple true primaries or metastatic disease. However, there is a clinical significance that metachronous MFOS is a potentially curable disease [Resnick D, Kyriacos M, Greenway GD. Tumors and tumor-like lesions of bone: imaging and pathology of specific lesions. In: Resnick D, editor. Diagnosis of bone and joint disorders. Philadelphia: Saunders, 1995: p. 3697-9.]. To our knowledge, there have been only a few reports about metachronous MFOS. We report a case of MFOS in a 14-year-old boy with review of the literature.