A case of malignant transformation of a benign chondroblastoma of the tibia in a fifteen-year-old boy is reported. The tumour was not irradiated at any time during the course of the disease. The tumour showed a typical appearance of benign chondroblastoma at the first operation. It recurred repeatedly after curettage, and finally emerged as a highly malignant undifferentiated sarcoma. In spite of amputation the patient died nine years after the onset of the disease with an enlarged liver and inguinal lymph nodes.

1. A clinical, radiological and pathological study of sixty-nine cases of epiphysial chondroblastoma has been made.

2. The nature of the tumour is discussed and its clinical and radiographic features are described. A special type is described, for which the name "cystic chondroblastoma" is suggested.

3. The results of treatment are described and the generally benign behaviourof the lesion is noted.

4. The occurrence of malignant change is noted and discussed.

The results of using Boplant in a series of thirty-three operations have been very disappointing. Pyrexia of over 100 degrees Fahrenheit followed operation in more than one-third of cases. There was an incidence of at least 36 per cent of failure to achieve the object of operation. Radiographic evidence of failure of incorporation was seen even in a number of clinically successful cases. As a result of this experience and of the experience of other surgeons in Winnipeg the use of Boplant has now largely been abandoned.

1. Alkaline and acid phosphatase, non-specific esterase and beta-glucuronidase have been estimated and demonstrated histochemically in a series of bone tumours and allied lesions, of which ten were osteogenic sarcomata, ten were giant-cell lesions, eleven were fibroblastic lesions and seven were tumours of cartilage.

2. Osteogenic sarcoma was found to be characterised by high levels of alkaline phosphatase, with rich staining for this enzyme in the tumour cells. Similar high levels of alkaline phosphatase were found in other bone-forming lesions, such as fibrous dysplasia, a giant-cell sarcoma with osteogenic matrix, and fracture callus.

3. Giant-cell lesions were characterised by high levels of acid phosphatase, and intense staining for this enzyme in the osteoclasts. These cells were also found to be rich in non-specific esterase (as shown by the alpha-naphthyl acetate method) and in beta-glucuronidase, but almost or entirely lacking in alkaline phosphatase. High levels of alkaline phosphatase were not found in giant-cell lesions except in relation to osteogenic matrix.

4. Fibroblastic tumours were characterised by moderate levels of all four enzymes, with little or no staining for phosphatases in the tumour cells; non-specific esterase was generally present in a proportion of the cells.

5. In certain lesions intermediate stages in the differentiation of fibroblasts to osteoblasts were found, notably in fibrous dysplasia, in which the biochemical change preceded the histological. In such lesions high total levels of alkaline phosphatase were found.

6. Cartilaginous tumours were characterised by low levels of all four enzymes, and little histochemical staining except in hypertrophied cells in areas of ossification.

7. It was found in general that the enzyme distributions in these neoplasms and other lesions reflected the findings in comparable reactive and growing normal tissues.

In 1948 Jaffe and Lichtenstein published a series of bone tumours as chondromyxoid fibromata, stressing that this newly recognised entity was likely to be mistaken for chondrosarcoma but was a benign growth. The accumulated experience of thirty-seven cases, which are all that have been recorded in detail, is briefly reviewed. A further series of nine similar cases is reported here and comparisons are made which show general agreement with the experiences and conclusions of earlier authors. It is however suggested that the tendency to recur may have been underestimated, particularly in younger patients.

1. A case of chondromyxoid fibroma of the tibia is reported.

2. Initial removal by curettage was followed by regrowth of residual foci; these were removed by a second curettage three years later. Re-examination after a further three years shows no evidence of regrowth, and suggests that cure has been achieved.

3. Some histological features of the neoplasm are briefly described.

1 . A case of parosteal osteoma with histologically low-grade sarcomatous areas is described.

2. Arteriography revealed abnormal arteries, the histological appearances of which are described.

3. Vascular shunts indicative of low-grade malignancy were also seen.

4. Reasons are given for accepting the view that this lesion is a tumour, originally benign, but liable to the development of low-grade malignancy.

A case of benign chondroblastoma in the upper end of the humerus is described. A plea is made that radiotherapy should be avoided in the treatment of this tumour. It is suggested that biopsy should be performed in every case.