Secondary chondrosarcoma in cartilage bone tumors: report of 32 patients.

BACKGROUND: Secondary malignancies arising from benign bone tumors are rare. Their recognition and diagnosis are difficult, and their slow growth and late recurrence require long-term follow-up. In this study, malignant transformation rates of various histological types of benign cartilage-forming bone tumors in large series were evaluated.

METHODS: Between 1986 and 2004, a retrospective analysis of 627 cartilage-forming benign bone tumors revealed that 32 patients had malignant transformation. Of the 32 patients, 14 had solitary osteochondromas, 10 had multiple osteochondromas, 6 had a solitary enchondroma, 1 had Ollier's disease, and 1 had Maffucci's syndrome. The patient with Ollier's disease had two chondrosarcomas, and one patient with multiple osteochondroma had three chondrosarcomas. The cases were included in the study only when complete clinical documentation, radiological records, and histological analyses were available.

RESULTS: The rate of malignant transformation for cartilage-originating tumors was 5.1% (solitary osteochondromas 4.2%, multiple osteochondromas 9.2%, solitary enchondromas 4.2%). The average time between the initial diagnosis and malignant transformation was 9.8 years. The most common site of involvement was the proximal portion of the femur. The tumors generally were well differentiated. The mean follow-up period was 57.3 months. Five patients (15.6%) died of tumor recurrence or metastasis at an average of 20.6 months. One patient is alive with tumor at 104 months.

CONCLUSIONS: Cartilage-forming benign bone tumors are rather prone to undergo malignant transformation. Although malignant transformation of a benign bone tumor is a rarely encountered situation, orthopedic surgeons should be cautious while following patients with a benign bone neoplasm. Early recognition and appropriate surgical treatment are required to achieve successful outcomes. The rate of local recurrence in secondary chondrosarcomas depends not only on adequate surgical treatment but also on the localization and histological grade.