Dedifferentiated parosteal osteosarcoma: the experience of the Rizzoli Institute.

BACKGROUND: Dedifferentiated parosteal osteosarcoma (DPOS) is a variant of osteosarcoma in which a high-grade sarcoma coexists with a conventional parosteal osteosarcoma (c-POS), either at presentation (synchronous type) or at the time of recurrence (metachronous type). Only approximately 60 patients have been reported in the literature. The objective of this study was to analyze the clinicopathologic and radiographic features of a relatively large number of patients with DPOS in an attempt to define further the histologic and biologic behavior of this rare entity.

METHODS: In a series of 120 patients with parosteal osteosarcoma who were seen at the Rizzoli Institute from 1958 to 2000, the authors identified 29 patients who were diagnosed with DPOS. The authors reviewed the clinical and radiologic features, histologic sections, treatments, and outcomes in this group of patients with DPOS.

RESULTS: Twelve patients were male, and 17 patients were female. The patients ranged in age from 15 years to 65 yrs (average, 36 years; median, 32 years). One tumor involved the scapula, one involved the ilium, and another involved the skull. All 26 of the other tumors were located in the long bones (14 in the femur, 5 in the humerus, 3 in the tibia, 3 in the fibula, and 1 in the ulna). In 18 patients, radiographic areas of lucency were seen within an otherwise sclerotic lesion. Histologically, the dedifferentiated component was high-grade osteoblastic osteosarcoma in 14 patients, fibroblastic osteosarcoma in 10 patients, giant cell-rich osteosarcoma in 3 patients, and chondroblastic osteosarcoma in 2 patients. All tumors were Stage IIB, and invasion of the medullary canal was detected in 19 patients (65%). Twenty-eight patients underwent surgery, and 18 of those patients received chemotherapy (5 patients received neoadjuvant chemotherapy, and 13 patients received adjuvant). Nine patients were dead and 20 patients were alive (average follow-up, 107 months; range, from 3 months to 36 years) at the last follow-up. Of the nine patients who died, one patient received no treatment, five patients underwent surgery (with three patients achieving adequate margins) in combination with chemotherapy, and three patients underwent surgery only (with adequate margins achieved). Of the 20 patients who remained alive, 13 patients underwent surgery (with 10 patients achieving adequate margins) in combination with chemotherapy, whereas 7 patients underwent surgery only (all with adequate margins). Seven of the nine patients who died had widespread metastases. One patient died of causes unrelated to the tumor, and another patient died shortly after undergoing resection of a lesion in the skull.

CONCLUSIONS: Dedifferentiation occurred in approximately 24% of patients with c-POS. The prognosis for patients with DPOS was better than the prognosis for patients with dedifferentiated central and dedifferentiated peripheral chondrosarcoma.