[Dedifferentiated chondrosarcoma. A study of 13 clinical cases and review of the literature].

PURPOSE OF STUDY: Dedifferentiated chondrosarcoma is a variant of chondrosarcoma of bone consisting in a highly anaplasic sarcoma associated with low grade chondrosarcoma. The histopathology and the poor prognosis characterize these tumors. The clinical, radiographical and histological features are described before proposing a therapeutic approach to improve prognosis.

MATERIAL AND METHODS: Thirteen cases of dedifferentiated chondrosarcoma having the histological requirements described by Dahlin and Beabout were identified and treated between 1977 and 1992 at the Cochin Hospital. These tumors represented 10 per cent of all chondrosarcomas registered in the same period. Eleven cases were primary and in two cases the dedifferentiated chondrosarcomas were first found in recurrent tumors. The average of age was 53 years. This was a retrospective study. The clinical reports, radiograms and histological reports were reevaluated. In doubtful cases the histological sections were reviewed.

RESULTS: The clinical features were no different from chondrosarcoma except for the high incidence of pathological fractures. The histology was associated in all cases with a grade 1 or 2 chondrosarcoma and a grade 3 or 4 anaplasic component. The anaplasic components were: 5 osteosarcomas, 5 fibrosarcomas, 2 fibrous histiocytomas, 1 rhabdomyosarcoma. All the patients underwent surgical treatment. Only one patient was treated by adjuvant chemotherapy. Among the eleven primary chondrosarcomas: two disarticulations were performed. En bloc resection was performed in nine patients: one wide margin, six marginal and two intralesional. The two secondary dedifferentiated chondrosarcomas were treated by disarticulation. No local recurrences were observed after disarticulation or wide resection. All patients presented pulmonary metastasis leading to death except one patient with only three months follow up. The average survival time was nine months (1 to 36 months).

DISCUSSION: Prognosis is uniformly poor. The five years survival rate is 0 per cent in our series and 10.5 per cent in the series published by Unni and Frassica. The physiopathologic hypothesis which prevails is that the two histologic components originate from two different primitive cell clones, one of which differentiates into a low grade chondrosarcoma while the others fails to differentiate and remains a high grade sarcoma expressing different morphologic features. Treatment was not always adequate, because the diagnosis was missed at time of biopsy in five cases. The biopsies showed the two histological components in only six cases. All our patients presented pulmonary metastasis excepted one patient. This feature was also noted in other series (70 to 100 per cent). Those metastasis originate from the anaplasic component. Chemotherapy has not been well evaluated for these tumors but its effectiveness is evident for treatment of osteosarcoma.

CONCLUSION: These tumors, which are characterized by their histology and their poor prognosis, are frequently inadequately treated. It is necessary to improve the prognosis: by performing a large biopsy adjusted on the lytic bone. by performing a wide resection or amputation. We believe that it is necessary to associate a chemotherapy to surgical treatment. We have decided to treat our patients with an osteosarcoma protocol.