Dedifferentiated chondrosarcomas arising in preexisting osteochondromas

Background: Dedifferentiated chondrosarcomas that arise in osteochondromas are extremely rare lesions for which very little information on treatment and outcome is available in the literature. The purpose of the present study was to describe the specific clinical, radiographic, and histologic features of this lesion and to evaluate the oncologic outcome after different treatment strategies. Methods: We reviewed the files of the Rizzoli Institute between 1970 and 2002 and identified eighteen patients for whom adequate records and histologic images were available and in whom a high-grade sarcoma had been diagnosed at the same location as a preexisting osteochondroma. Radiographic studies, histologic slides, and clinical records were reviewed, the features of those studies were tabulated, and prognostic features and the results of treatment were identified. Results: The patients included twelve men and six women with an average age of forty-six years (range, twenty-two to seventy-four years). Eight lesions occurred in patients with multiple osteochondromas, and ten occurred in patients with solitary lesions. The most common locations were the pelvis (six lesions) and the femur (five lesions). Symptoms included pain, swelling, and a growing mass; the average duration of symptoms was eighteen months. Radiographically, ten lesions appeared as a conventional secondary chondrosarcoma arising in an exostosis, whereas eight showed typical signs of dedifferentiation. Histologic evaluation of the cartilage component demonstrated thirteen grade-1 and two grade-2 chondrosarcomas. In three cases, no cartilage component was recognized. The dedifferentiated component was considered to be an osteosarcoma in nine cases (including six cases in which it was osteoblastic and three in which it was fibroblastic), a malignant fibrous histiocytoma in eight, and a fibrosarcoma in one. The dedifferentiated component represented an average of 59% (range, 20% to 100%) of the lesion. For the fifteen patients who were Managed at the authors' institution, the two and five-year survival rates were 47% and 29%, respectively; the median survival time was fourteen months. Patients who were managed with a combination of surgery and chemotherapy had a better overall survival rate than did those who were managed with surgery alone (p = 0.03). Conclusions: Dedifferentiated chondrosarcoma arising in a preexisting osteochondroma is an extremely rare lesion with a poor prognosis. In the present small series, overall survival was better when wide surgical resection was combined with adjuvant chemotherapy. Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.