Abstract
Six cases are reported in which a fibrosarcoma or malignant fibrous histiocytoma developed in relation to an enchondroma in a long bone. Four of the tumours were fibrosarcomata, and two were malignant fibrous histiocytomata. Five of the six cases were in the distal femur, which is a common site for old calcified enchondromata or "cartilage rests". The age of the patients was between fifty-six and eighty-six with a mean of seventy. Four were women, Five died less than one year after presentation. The fibrosarcomata and malignant fibrous histiocytomata do not appear to have arisen directly from the tumour cartilage but from the dense fibrous tissue surrounding necrotic areas in the enchondromata by a process analogous to that responsible for the development of fibrosarcomata in bone infarcts and chronic osteomyelitis. The possibility that some "dedifferentiated" chondrosarcomata are forms of collision tumour is discussed.
