It is an aggressive subtype of metaplastic breast carcinoma in which there is a direct transition from carcinoma to the osseous, chondroid, or chondromyxoid elements. Well-formed bone and cartilage are absent. The carcinoma is usually invasive high-grade ductal carcinoma and necrosis is frequently present. In this image, the tumor cells are in direct contact with chondromyxoid matrix. Note the absence of intervening spindle cell component. Metaplastic breast carcinomas are a heterogenous group of tumors, including spindle cell carcinoma (fibromatosis-like; fibrosarcoma-like), sarcomatoid carcinoma, carcinosarcoma, matrix producing carcinomas, metaplastic high-grade adenosquamous carcinoma, carcinoma with osteoclast-like giant cells, and metaplastic carcinoma with choriocarcinomatous areas. Ref: Downs-Kelly E, et al. Matrix-producing carcinoma of the breast : An aggressive subtype of metaplastic carcinoma. Am J Surg Pathol 2009:33:534-541.