Estradiol receptor in human breast cancers throughout the menstrual cycle.

The existence and the concentration of the estradiol receptor (ER) in breast cancers of pre- and postmenopausal patients were measured. ER status and concentration are significantly higher in cancers of postmenopausal women. Breast cancers operated at various phases of the menstrual cycle showed remarkable differences in ER incidence and concentration. The highest values were found in the early proliferative phase, whereas the ER incidence is lowest in cancers which were operated at early secretory phase. ER concentrations found in late proliferative and late secretory phases are significantly lower than those found in cancers of postmenopausal patients. Statistically significant differences of the ER concentrations between the various phases of the menstrual cycle could not be secured.