Purpose: In our records on bone tumours, secondary chondrosarcomas account for slightly less than 15% of all chondrosarcomas (20/150). The presentation is quite variable making diagnosis relatively difficult. We reviewed our experience to evaluate diagnosis, frequency, and prognosis.

Material and methods: From 1981 to January 2002, we had 20 chondrosarcomas which developed on pre-existing lesions: solitary exostoses (n=11), solitary chondroma (n=1), multiple exostosis (n=6), multiple enchondromatosis (n=2). Localisations were: pelvis (n=9), femur (n=3), humerus (n=2), tibia (n=3), spine (n=2), scapula (n=1). Histological classification was: grade I (n=7), grade II (n=9), grade III (n=1), and dedifferentiated sarcoma (n=3). Surgery was performed in all patients, alone for grade I and II chondrosarcoma, in association with chemotherapy (n=3) and radiotherapy (n=1) in three patients with dedifferentiated sarcoma.

Results and prognostic factors: At last follow-up (mean 9 years 10 months), five patients had died after local recurrence (n=3) or metastatic dissemination (n=2). The other fifteen patients were living (mean follow-up 155 months). The main prognostic factor was histological grade of chondrosarcoma. All patients with grade I chondrosarcoma (n=7) survived versus only two-thirds of those with grade II chondrosarcoma and half (2/4) of those with grade III or dedifferentiated chondrosarcoma. The second prognostic factor was initial management. Inadequate care initially led to misdiagnosis or delayed diagnosis (n=4), local recurrence (n=3) and loss of chance of survival (n=3). Grade I chondrosarcoma was occasionally taken for benign exostosis despite a cartilage cuff measuring more than 1 cm, normally a sign of chondrosarcoma.

Conclusion: 1. Because of the severity of secondary dedifferentiated chondrosarcoma, resection should be performed in adults presenting exostosis with a large residual cartilage cuff, particularly in high-risk locations (pelvis). 2. Because of the difficulty in recognising the histological features of grade I chondrosarcoma, the diagnosis of degeneration should be retained in adults if the cartilage cuff exceeds 1 cm. Lesions are suspicious if the cartilage cuff exceeds 5 mm.