Breast Cancer - Hormone Replacement Therapy

Low-Potency Estrogen Pills Linked to Cancer
Low-potency estrogens, such as estriol used orally or in vaginal creams, have been prescribed to many women to relieve symptoms of vaginal atrophy and dryness, particularly in Europe. It has never been clear whether these estrogens are safer than the higher-potency formulations, such as estradiol and conjugated estrogens (Premarin) that are often used to treat hot flashes and night sweats. High-potency estrogens are known to increase risk of uterine cancer unless accompanied by a progestin. They also increase breast cancer risk regardless of whether progestins are added.

In a case-control study at Stockholm's Karolinska Institute including 789 women with uterine (endometrial) cancer and 3,368 controls, oral low-potency estrogens were linked to cancer risk, just as stronger estrogens are. Women using low-potency estrogen pills had double the cancer risk of women who had never used them, and triple the risk if they used them for five years or longer. Risk quickly dropped with discontinuation of use. Vaginal application was not associated with cancer risk. However, this result does not apply to vaginal use of more potent estrogens.

Weiderpass E, Baron JA, Adami HO, et al. Low-potency oestrogen and risk of endometrial cancer: a case-control study. Lancet. 1999;353:1824-8.

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