Proliferative and secretory activity in human breast during natural and artificial menstrual cycles

Abstract

Events of cell proliferation have been assessed by thymidine labeling index (TLI) in morphologically normal breast lobules from women of reproductive age. TLI is higher during the second half of the menstrual cycle both in women with natural menstrual cycles and in those with artificial cycles due to oral contraceptive (OC) use. TLI varies between 0.04% and 5.7% and declines with increasing age. There is no difference in mean TLI between OC users and nonusers if correction is made for the difference in age distribution between these two groups. Immunohistochemical detection of immunoglobulin A (IgA), secretory component (SC), and alpha-lactalbumin shows more frequent positive staining during artificial than natural menstrual cycles, and positive staining tends to be associated with higher TLI values. No significant variation in staining with cycle phase is detected in natural or artificial cycles. These results show that breast tissue does not resemble endometrium in the relationships that exist between proliferation, secretion, and menstrual cycle phase.

PIP: This study examines the relationships of mammary epithelial cell proliferation and secretory activity to the phase of the menstrual cycle in both natural menstrual cycles and those artificially regulated by oral contraceptives. Breast tissue was taken from 138 women with normal (26-30 day) menstrual cycles, hospitalized for biopsy or mastectomy. Date of last menstrual period was recorded and the tissue labeled with tritiated thymidine. Only morphologically normal lobules were used. Immunologic staining was done to reveal alpha-lactalbumin, alpha chains of immunoglobulin A, and secretory components. Since thymidine labeling index is known to decline with age, and hence with parity and oral contraceptive use, samples were standardized to age 30. In both natural and artificial cycles, maximum proliferation of mammary epithelium occurred in the latter half of the cycle. Immunoglobulin A and secretory component were detected more frequently during artificial menstrual cycle than during natural ones, and they tended to be associated with high thymidine labeling index values. The study confirms the predominance of proliferative events during the secretory phase of the cycle and the lack of any significant relationship between proliferation and secretion in the resting breast. The study also shows that the relationships between proliferation, secretion, and menstrual cycle phase exhibited by breast tissue are different from those exhibited by the endometrium.