Adenosquamous differentiation in mammary carcinoma: an ultrastructural and steroid receptor study.

Five breast carcinomas with only squamous morphology by light microscopy demonstrated ultrastructural features of both squamous and adenomatous differentiation within the same individual cells. Two of the five cases demonstrated quantitatively low levels of saturable estrogen- and/or progesterone-binding proteins. In no case were there quantitative or qualitative patterns of receptors indicative of clinical hormonal response potential. It is suggested that primary squamous cell carcinomas of the breast should be examined ultrastructurally for adenosquamous differentiation as each of the five apparent squamous carcinomas observed in a prospective study of 1,760 (0.3%) cases of breast cancer demonstrated adenosquamous differentiation ultrastructurally.