The pill and the breast
Drife, J.O.
Ippf Medical Bulletin 18(6): 1-2
1984
ISSN/ISBN: 0019-0357 PMID: 12313402 Document Number: 240314
Discussion focused on the role of the ovarian steriods, estrogen and progesterone, in the development of breast cancer, the effects of natural and synethic hormones on breast tissue, and recent epidemiological studies concerning breast cancer and the use of oral contraceptives (OCs). Apparently, ovarian hormones play a role in the development of breast cancer. Late menarche, early menopause, and the removal of the ovaries provides some protection against breast cancer. Women who experience a full term pregnancy also have a reduced risk, and the level of protection is increased if the pregnancy occurs early in the reproductive life span. Little is known about how these protective effects operate. It is known that estrogen proliferates endometrial cells and that progesterone checks this growth. Unchecked proliferation can produce malignant cells. Perhpas during pregnancy, breast epithelium becomes more responsive to progesterone, or perhaps the increased progesterone levels which prepare the breast for lactation alter the growth of breast epithelium. Changes in breast tissue during the course of the menstrual cycle, which could be attributed to the altering levels of ovarian hormones during the cycle, appear to be minimal; however, recent investigations report that DNA synthesis and mitotic counts in breast tissue increase during the 2nd half of the menstrual cycle. These findings indicate that progesterone might stimulate breast activity. The effect is the opposite of that observed for endometrial proliferation which occurs during the 1st half of the cycle in response to estrogen. One would expect that breast activity would also be increased for women who use OCs, but preliminary studies indicate that OCs do not overstimulate breast epithelium. Perhaps breast tissue is less responsive to synthetic hormone or perhaps OCs inhibit progesterone receptor synthesis. It is difficult to assess the epidemiological evidence concerning a link between breast cancer and OC use because the studies are based on only a few cases, the effects are delayed over many years, and most of the subjects in the studies took OCs when only high dose preparations were available. These studies include 1) a California study of 163 women, which found that OC use prior to 1st pregnancy increased the risk of breast cancer; 2) an additional 151 cases analyzed at a later date in the California study, which indicated that OC use, prior to age 25, increased the risk of breast cancer; and 3) a British study in which the addition of 27 cases to a previous study of 1176 cases to the reversal of earlier findings and indicated that prolonged use of OCs prior to last pregnancy increased the risk of breast cancer.