FROM THIE SECTIONS ON SURGERY AND PATHOLOGY OF THE VICKSBURG CLINIC, VICKSBURG, MISS. AREAS of calcification and ossification, and even of true bone formation, are not uncommon findings in certain inflammatory and neoplastic conditions, particularly in lesions capable of exciting localized hematomas or areas of necrosis. Calcifications and ossifications of this kind have also occasionally been observed in fibrosarcomas arising in soft tissues. In none of the latter instances, however, do the bone elements seem to be formed by the cells of the neoplasm.In contrast to these relatively frequent observations, the neoplastic cells of a certain rare group of fibrosarcomas of the soft tissues apparently exhibit a perverted tendency to form bone. The perversion is accompanied by other manifestations of osteogenic sarcoma, including the presence of large numbers of foreign body giant cells of the osteoclastic type. Tumors in which this bone-forming process occurs are classified as extraskeletal osteogenic sarcomas.In I94I, Wilson' was able to collect from the literature 30 cases of "bone-forming malignant tumors in the soft parts," to which he added ten other cases of "extraskeletal ossifying tumors," six from the Registry of Bone Sarcoma of the American College of Surgeons and the remainder from the Departments of Surgery and Pathology of the University of Chicago. Three of the ten new cases represented benign growths, and Wilson mentions other nonmalignant cases of extraskeletal ossifying tumors not included in the 30 cases of sarcoma which he collected from the literature.Wilson points out that myositis ossificans offers problems of differential diagnosis, and it seems reasonable to assume that a case or two of this condition may possibly be included in the 30 cases he collected from the literature, because of the notorious tendency of myositis ossificans to simulate sarcoma histologically. Definite statements cannot be made on this point, since no attempt has been made to review the original material, but it might be said that such an error could occur only in a patient who was cured by local excision of his tumor. In most of the reports, because either recurrence or metastasis was demonstrable, the malignancy of the lesion seems beyond question.Of the 30 extraskeletal malignant tumors collected from the literature by Wilson, seven, or nearly 25 per cent, were osteogenic sarcomas of the thyroid gland, and I2 or 40 per cent, were osteogenic sarcomas of the breast. Four tumors occurred in the thigh and one each in the gallbladder, the chest wall,