Previously diagnosed or suspected cancer of the uterus is one case in point. During the mid-1970s, when higher levels of estrogen were used than today, estrogen was found to increase the number of cases of uterine cancer by four to eight times. Although estrogen itself does not cause cancer, it can cause hyperplasia, or the buildup of cells of the uterine lining. But it should also be noted that HRT with progesterone actually decreases the risk of endometrial cancer to levels even lower than if not taking estrogen at all. Another contraindication is previously diagnosed or suspected estrogen-dependent breast cancer.
Breast cancer is one of the most common cancers of women.
In fact, one out of nine women will develop breast cancer in her lifetime. Estrogen can stimulate the growth of existing breast cancer, and may promote a recurrence of the disease, according to some studies. However, many experts believe that estrogen replacement does not increase the risk of breast cancer in the short term, defined as up to 15 years by some. The long-term risk of greatest concern is breast cancer. At this point, it is believed that women who stay on HRT for more than 10 years have an increased risk of breast cancer.