[Breast cancer and estrogen receptors: its clinical significance and problems].

The clinical usefulness of estrogen receptor (ER) assays in the management of breast cancer has been established. However, several problems remained. In this paper, the problematic aspects of ER such as the molecular forms, inter-site variations, relationships to histological pattern, with regard to the effectiveness of chemotherapy and to prognosis, and ER in male breast cancer, are reviewed and discussed.