Myoepithelial carcinoma of the breast with distant metastasis and accompanied by adenomyoepitheliomas.

A breast tumour in a 47-year-old female with axillary lymph node metastasis was interpreted as the rare malignant adenomyoepithelioma based on morphological and immunohistochemical studies. Multiple bone metastases developed and the patient died after 7 months. The malignant neoplasm consisted of cords and interlacing bundles of spindle cells with indistinct cell borders and clear cytoplasm. The cells stained positively for cytokeratin, S-100 protein, GFAP, and muscle-specific actin, and possessed basal lamina, pinocytic vesicles, tonofilaments, desmosomes, and intermediate filaments with dense bodies. In some areas, cells with microvillous projections enclosed small spaces. In the breast, foci of myoepithelioma with various morphological subtypes and infiltration coexisted, demonstrating the origin of the malignant tumour. The histogenesis of the myoepithelial tumours is discussed.