Proliferation of breast epithelial cells in healthy women during the menstrual cycle

Objective: Our objective was to assess proliferation in normal breast epithelial cells from healthy women during the follicular and luteal phases of the menstrual cycle. Study design: We analyzed the proliferation marker Ki-67/MIB-1 by immunocytochemical methods in breast epithelial cells procured through fine needle aspiration biopsy from 47 healthy volunteers. Differences were assessed by Wilcoxon rank sum tests, and correlations were determined by Spearmanʹs rank correlation coefficient. Results: The proportion of KI-67/MIB-1-positive cells was higher in the luteal phase (2.04%) than in the follicular phase (1.66%). The values in women aged <35 years were 2.29% and 1.13%, respectively (p=0.003). In ovulating women with two aspirates during the same menstrual cycle the percentage of proliferating cells increased from the follicular phase (1.3%) to the luteal phase (2.4%) (p<0.04). Proliferation was positively correlated with serum progesterone levels the day of aspiration (r=0.34, p<0.05). Conclusion: The fine needle aspiration biopsy technique is a valuable tool for in vivo studies of cell proliferation in the normal breast. Data clearly suggest a proliferative action of progesterone.