MALIGNANT ADENOMYOEPITHELIOMA OF THE BREAST WITH MIXED OSTEOGENIC, SPINDLE-CELL, AND CARCINOMATOUS DIFFERENTIATION

A 50-year-old woman had a malignant tumor of the left breast, which re curred twice, metastasized, and caused death after 39 months. Histolog ically, the original neoplasm and the first recurrence comprised an ad enomyoepithelioma, in addition to a sat-coma composed of trabeculae of mature and immature bone, osteoid, and partly calcified, dense collag enous tissue. The trabeculae were lined by alpha-smooth muscle actin-p ositive mononuclear tumor cells, which also extended into the stroma. Similarly, scattered osteoclastlike, multinucleate giant cells were pr esent in the stroma and in the region of the trabeculae. This same pat tern of adenomyoepithelioma and osteosarcoma also was seen in the last recurrence, together with a proliferation of undifferentiated maligna nt spindle-shaped cells. The last biopsy also contained a separate sma ll focus of invasive ductal carcinoma of usual type. It was concluded that this, apparently unique, tumor probably represented an adenomyoep ithelioma in which a metaplastic sarcoma of osteogenic and undifferent iated types developed from the myoepithelial element, and in which a c arcinoma developed from the epithelial component.