Four examples are reported of an unusual noncystic intraosseous lesion which does not conform to any hitherto recognized entity and which can be mistaken, not only by the general histopathologist but by the osteoarticular pathologist, for a variety of other conditions, including sarcoma and giant‐cell tumor. They were in patients aged 5 to 13 years; three in the spine, one in the ethmoid. Local excision, supplemented by low‐dose radiotherapy in cases with cord compression, produced a satisfactory outcome in all cases. At presentation the radiologic findings were nonspecific but, following treatment, an eggshell rim of bone developed in those lesions which had been incompletely excised. Histologically, they are characterised by florid fibroblastic or fibrohistiocytic proliferation, osteoblastic differentiation with osteoid production, areas rich in osteoclast‐type giant cells, aneurysmal sinusoids, and occasional foci of degenerate calcifying fibromyxoid tissue. Because this combination of histologic features can be found in the solid parts of aneurysmal bone cyst and in no other condition, at this centre we have regarded this lesion as a variant of aneurysmal bone cyst devoid of any cystic component.

Eighty-six cases of giant cell bone tumor were reviewed with particular attention to frank sarcomatous changes, abnormal mitoses, permeation of vascular channels, and the number of mitoses per square millimeter, and the results were analyzed in relation to malignancy, aggressiveness, and recurrence. There were 4 cases of malignant (Grade III) tumor (about 5%) showing frank sarcomatous changes. Eight (9%) were considered cases of borderline (Grade II+) tumor, without frank sarcomatous changes but showing abnormal mitoses or vascular permeation. Seventy-four (86%) were cases of conventional giant cell tumor (Grades I and II). Mitotic counts did not categorically distinguish the three groups because of overlap. Recurrence essentially reflected the inadequacy of treatment. Metastases were observed only in the malignant group. About a quarter of conventional giant cell tumors were considered aggressive on clinical or radiologic grounds, but these could not be identified on a histologic basis. Tumors with minimal mitotic activity (1/mm2 or less) were almost exclusively nonaggressive. Post-irradiation sarcomas, best regarded as independent new tumors, developed in 4 cases (about 5%).

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.

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