Exostosis: development, evolution and relationship to malignant degeneration.

The authors report a study of 408 cases of exostosis (318 single and 90 multiple) from the records of the Tumour Centre of the Rizzoli Institute. Special attention was paid to the relationship with peripheral chondrosarcoma, 73 cases of which are also in the records of the Institute, and were separately studied. The authors conclude that it is impossible to determine the incidence of malignant transformation of solitary exostosis. The incidence of malignant transformation of multiple exostoses in the present case material was 13 per cent, but the true incidence would undoubtedly be higher if all patients were followed up for life.