A recurrent spinal tumor confidently diagnosed as osteoblastoma eventually terminated as a sclerosing osteoblastic which metastasised nine years after the onset of symptoms.

Sixty-two cases of chondrosarcoma of bone were reviewed and histologically graded as low, medium or high-grade tumours. After excluding patients dead from unrelated causes or lost to follow-up, forty cases were available for ten-year follow-up and fifty-eight for five-year follow-up. The rates of survival, recurrence and metastasis were analysed according to the histological grading. Recurrence was further analysed according to the adequacy of treatment. The results were compared with those previously reported in the literature. There was a ten-year survival rate of 58 per cent. Recurrence developed in 58 per cent and was uncontrollable in 29 per cent. The recurrence rate was 87 per cent with inadequate treatment and 15 per cent with adequate treatment. Recurrences outside the limb bones usually proved uncontrollable; recurrences in the limb bones were amenable to further, and if necessary repeated, operations. High-grade chondrosarcoma had a metastatic risk of 75 per cent and eventual mortality of 88 per cent. Medium-grade chondrosarcoma had a metastatic risk of 14 per cent and a mortality of 60 per cent. Low-grade chondrosarcoma had a metastatic risk of 5 per cent and a mortality of 29 per cent.

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.

Old calcified fibrin coagula are frequently found in simple bone cysts. They provide a scaffold on which new bone is laid down, in a process analogous to endochondral ossification. It is suggested that these coagula are derived in substantial part from the plasma-like contents of the cyst, after the release of plasma-clotting factors as the result of injury. Major haemorrhage is not involved and in many cases there is no antecedent fracture. The phenomenon is not seen in other common cystic conditions of bone and its recognition is thus helpful in the histological diagnosis of simple bone cyst. Cystic bone infarcts and their possible confusion with simple bone cysts are also briefly discussed.