Carcinomas of the breast showing myoepithelial cell differentiation. A review of the literature.

Myoepithelial cells are normally located between the epithelial cells and the basal lamina of secretory elements of exocrine glands. Their role in the histogenesis of breast tumours has been studied extensively, and a definite differentiation towards myoepithelial cells has been demonstrated in adenoid cystic carcinoma, adenomyoepithelioma, low-grade adenosquamous (syringomatous) carcinoma, pure malignant myoepithelioma and poorly differentiated myoepithelial-rich breast carcinoma. All these tumours are of low malignancy, with the exception of malignant myoepithelioma and poorly differentiated myoepithelial-rich carcinoma. When a low-grade tumour is associated with a spindle cell component, distant metastases must be expected. Pure malignant myoepithelioma shows morphological and clinical features similar to those of monophasic sarcomatoid carcinomas, and it is possible that this last tumour is linked histogenetically to sarcomatoid carcinomas.