Bone-containing neoplasms which have no connection with the skeleton are occasionally observed in man. Raso (1), in 1937, reported an osteoid chondrosarcoma of the breast and collected from the literature, dating from 1835, 74 mammary gland tumors containing bone or cartilage. Of the malignant tumors in this group, 27 were osteosarcomata, chondrosarcomata, or osteochondrosarcomata, 7 were primarily carcinomata, and 5 were mixed tumors. Binkley and Stewart (2) in 1940 discussed 9 cases of tumors of epithelial origin resembling osteogenic sarcomata and concluded that the most important alterations leading to the appearance of the structure of osteogenic sarcoma are the laying down of dense hyaline tissue and the development of a cavernous telangiectatic type of circulation favoring stasis. They recognized that these features fail to explain the structure of cartilage in these so-called mixed tumors. Allen (3), 1940, described 4 mixed tumors of the mammary glands of dogs and one from the human breast. He con...