[Hormone receptor system]

The expression, structure and function of estrogen receptor (ER), and the mechanism of action of hormonal treatments of breast cancer were discussed in order to formulate the rationale for the hormonal treatment of patients with advanced and/or recurrent breast cancer. The ER molecule were not observed in the epithelial cells of normal breast tissues, but they appeared in the cells of either hyperplastic adenosis or cancer. The ER negative cells, however, were existed in some degree even in ER rich cases. The ER staining was positive during almost all stages of cell cycle of ER positive breast cancer cell line. The estrogen-dependent growth of breast cancer has been proven to be mediated with the ER system. The structural change of ER after binding with estradiol provokes the expression of growth relating protein genes and put the cells into the DNA synthetic stage of cell cycle. On the other hand, the mechanism of action of hormonal treatment of breast cancer is mainly demonstrated through the interference on the function of ER. The cells sensitive to hormonal treatment are stabilized within the G0-G1 stages of cell cycle. The hormone non-dependent cells escape from these effects of treatment. Therefore, the exclusive hormonal treatment has only a limited indication for patients with advanced or recurrent breast cancer. Concomitant chemoendocrine therapy should be as the treatment of choice in those cases. The suitable combination of drugs, the duration of treatment, the sequential administration or withdrawal of drugs, should be analyzed. The possible usefulness of "missile therapy" targeting ER or growth factors using radio-labeled estradiol or anti-growth factor antibodies was suggested.