Researchers from the University of California, San Francisco, analyzed data from 30 different studies that used adequate controls and risk estimates. These studies essentially concerned hormone replacement therapy (HRT) and endometrial cancer risk. The findings, as published by the U.S. National Library of Medicine, revealed, Endometrial cancer risk increases substantially with long duration of unopposed estrogen use, and this increased risk persists for several years after discontinuation of estrogen. The study also indicated, although not statistically significant, the risk of death from endometrial cancer among unopposed estrogen is increased as well. The National Cancer Institute (NCI) further states that long-term exposure of the uterus to estrogen alone increases a womans risk of endometrial cancer. Although the risk associated with estrogen plus progestin use is apparently much less, some data does suggest the risk is still increased compared with the risk for nonusers. The NCI indicates the long-term effects of estrogen plus progestin on endometrial cancer risk are ultimately unclear. When results from the WHI Estrogen-plus-Progestin Study were analyzed, endometrial cancer rates for women taking both hormones were the same or potentially less than those women not taking HRT. A common side effect from estrogen plus progestin, however, was uterine bleeding, which is a possible sign of endometrial cancer. This, in turn, led to more frequent biopsies and ultrasounds for women compared to those not on HRT. The Million Women Study also confirmed a lower risk of endometrial cancer among women taking estrogen plus progestin compared to those taking estrogen only. According to the American Cancer Society (ACS), estrogen plus progestin therapy may help reduce menopause symptoms in women who still have a uterus without increasing their risk of developing endometrial cancer.
The Effects of HRT on Ovarian Cancer
The ACS indicates that ovarian cancer is rare, which lends an elusive quality to determining its risk factors. Even when a factor increases the probability of developing ovarian cancer, a womans absolute risk still remains relatively low. A woman, for example, is much more likely to be impacted by a 50 percent increase in her risk for breast cancer than by a 50 percent increase in her risk for ovarian cancer, simply because chances of developing ovarian cancer are much lower to begin with. Despite the odds, the ACS indicates ovarian cancer is often fatal. A minute risk associated with HRT, therefore, is worth considering. As such, the NCI has conducted analyses of ovarian cancer findings. The use of estrogen alone is associated with a slightly increased risk of developing ovarian cancer for women who use the hormone for 10 or more years. One observational study of more than 44,000 women over 20 years concluded those who used estrogen alone or more than 10 years were twice as likely to develop ovarian cancer compared with women who did not use HRT. Another similar study concluded estrogen use is linked to death from ovarian cancer. The Million Women Study revealed similar results as those from the observational studies. Women currently using menopausal hormones have an increased risk of developing ovarian cancer and a 20 percent likelihood of dying from the disease compared to non-users. The increased risk, however, often disappears after hormone use stops. According to the ACS, it is unclear if estrogen plus progestin use increases the risk of ovarian cancer. Data presented from the WHI study revealed that continuous HRT therapy of this sort may slightly increase the risk of developing ovarian cancer. This finding, however, may also have been linked to other factors because only a small number of women developed ovarian cancer during the study. Other studies also suggest that estrogen plus progestin use may slightly increase risk, but less than estrogen only use.
Sources: http://www.ncbi.nlm.nih.gov/pubmed/7824251 http://www.cancer.gov/cancertopics/factsheet/Risk/menopausal-hormones http://www.cancer.org/cancer/cancercauses/othercarcinogens/medicaltreatments/menopausal-hormone-replacement-therapy-and-cancer-risk
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