"Skip" metastases in osteosarcoma.

Careful study of 40 cases of osteosarcoma without evidence of multifocal disease, pulmonary metastasis, or history of exposure to predisposing factors has given histologic evidence of microscopic foci of osteosarcoma separate from the primary focus of osteogenic sarcoma. These "skip" lesions are to all pathologic examination completely separate from the primary focus of osteogenic sarcoma. They are more often found proximal to the primary, both intraosseously and transarticularly. Histologically, these "skips" represent areas of osteosarcoma which in many cases are a less-differenitated form of the tumor. The natural history of such tumors with "skips" following ablative surgery is an increased incidence of local recurrence and subsequent pulmonary metastases.