PAROSTEAL OSTEOSARCOMA - A CLINICOPATHOLOGICAL STUDY

The records of 226 patients (sixty-seven who were managed at our insti tution and 159 who were identified from the consultation riles) who ha d had a parosteal osteosarcoma were reviewed. The criteria for diagnos is were that, roentgenographically, the lesion had arisen from the sur face of the bone and that, histologically, the tumor was well differen tiated (Grade 1 or 2); it was characterized by well formed osteoid wit hin a spindle-cell stroma; and, when there was medullary involvement, less than 25 per cent of the medullary cavity was affected. Dedifferen tiation was more common (16 per cent of the patients) than previously reported and was associated with a poor prognosis. Cross-sectional ima ging studies demonstrated medullary involvement in 22 per cent of the patients, an unmineralized soft-tissue mass peripheral to the mineral component in 51 per cent, and adjacent soft-tissue invasion in 46 per cent. In contrast to the findings in our previous studies, medullary i nvolvement was not a poor prognostic factor. At an average of thirteen years (range, two to forty-one years), eleven of the sixty-seven pati ents who were managed at our institution died of the tumor; ten of the se patients had a dedifferentiated tumor. Statistical analysis of the thirty-nine patients who had had the primary treatment at our institut ion revealed that incomplete resection was associated with an increase d risk of local recurrence and that dedifferentiation markedly increas ed the risk of metastasis.