Influence of the menstrual cycle on the concentrations of estrogen and progesterone receptors in primary breast cancer biopsies.

There is controversy in the literature regarding the effects of endogenous hormones on estrogen receptors (ER) and progesterone receptors (PR) in young women with breast cancer. We studied 117 young women with primary breast cancer and assessed their breast biopsies for ER and PR. The women had a record of their last menstrual period prior to breast biopsy. The menstrual cycle was divided into four phases--early proliferative (days 1-7), late proliferative (days 8-15), early secretory (days 16-22), and late secretory (days 23-30). There were lower levels of both ER and PR in biopsies excised during the early secretory phase than in other phases of the cycle; early proliferative phase receptor positive medians of ER = 77 fmol/mg protein and PR = 467 fmol/mg protein fell to ER = 28 fmol/mg and PR = 128 fmol/mg protein in the early secretory phase.