Conjugated equine estrogen may increase risk for ovarian cancer

Conjugated equine estrogen (CEE) taken alone for menopause may increase the risk for developing and dying from ovarian cancer, according to a study presented at the annual meeting of the American Society of Clinical Oncology, held from May 31 to June 4 in Chicago.

Rowan T. Chlebowski, M.D., Ph.D., from the Lundquist Institute in Torrance, California, and colleagues conducted a long-term follow-up analysis of two randomized clinical trials as part of the Women’s Health Initiative (1993 to 1998). The analysis included data from 40 U.S. research centers that enrolled 27,347 women (aged 50 to 79 years) who had been through menopause but who had not had breast cancer or another type of cancer within the preceding decade. The participants who had had a hysterectomy received CEE (5,310 patients) or placebo (5,429 patients), while participants with a uterus received CEE plus medroxyprogesterone acetate (MPA; 8,506 patients) or placebo (8,102 patients).

The researchers found that at 20-year follow-up, patients in the CEE-alone group were twice as likely to develop ovarian cancer and nearly three times more likely to die from ovarian cancer compared with those who received the placebo (hazard ratios for incidence and mortality, 2.04 and 2.79, respectively). This increased risk for developing ovarian cancer began at 12 years and persisted over time. Compared with those receiving placebo, among participants receiving CEE plus MPA, there was no increased risk seen for developing or dying from ovarian cancer. Additionally, compared with those receiving placebo, participants receiving CEE plus MPA had a lower risk for developing uterine cancer; however, no benefit was seen for uterine cancer mortality.

“Our study provides the only long-term information from a randomized clinical trial on two common cancers in postmenopausal women for two of the most commonly used medications,” Chlebowski said in a statement.

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