Expression and modulation of estrogen receptors in human breast cancer.

Estrogen receptors have been traced at the tissue level in premalignant and malignant changes of human mammary gland by an immunoperoxidase technique using a monoclonal antibody against the receptor protein. Proliferative premalignant cells show an increased and homogeneous expression of the estrogen receptor by this technique; it seems that a constitutive expression of the receptor may play a role in the promotional carcinogenetic process. Moreover, infiltrating tumors show a striking heterogeneity in the cellular expression of estrogen receptor, which seems related to differentiation level.