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Ospemifene found to have minimal effects on the endometrium at 52 weeks

Breaking news and highlights from ACOG's Annual Clinical Meeting in Chicago, Illinois



Ospemifene was FDA-approved in 2013 to treat moderate to severe dyspareunia, a symptom of vulvar and vaginal atrophy (VVA) due to menopause. This nonestrogenenic drug has tissue selective agonist/antagonist effects—a selective estrogen-receptor modulator (SERM). Tamoxifen, a first-generation SERM, increases the risk of endometrial cancer. However, the second-generation SERM raloxifene is not associated with this increased risk. In preclinical studies and clinical trials, ospemifene has been shown to exert positive effects on the vaginal epithelium and minimal effects on the endometrium.

Steven R. Goldstein, MD, from New York University School of Medicine, and colleagues set out to determine the endometrial safety of ospemifene in six Phase 2/3 clinical trials of postemenopausal women with up to 52 weeks of exposure to ospemifene 60 mg/day versus placebo.

Endometrial safety of the study drug was assessed in a total of 1,349 women with an intact uterus (851 in the ospemifene group vs 543 in the placebo group).

Endometrial biopsies obtained at 52 weeks revealed a rate of endometrial hyperplasia of 0.3%.

Of 342 biopsied women, “there was a single case of a woman with simple hyperplasia,” says Dr. Goldstein. “She was 52 years old, had become menopausal at age 49 and had been taking hormone therapy for about 2 years before entering the trial. After 4 months of ospemifene, she had an episode of bleeding and was diagnosed with proliferative endometrium. The study drug was stopped with a plan to follow up in 3 months; 89 days later she had another episode of bleeding and was diagnosed with simple hyperplasia. She was treated with a single course of progestogen, the hyperplasia resolved, and then she was noted to have a benign polyp.”

No complex hyperplasias or carcinomas were found.

Ospemifene participants with histologic findings other than inactive, atrophic, or insufficient was 3.5% at 52 weeks, and this finding was similar to baseline endometrial biopsy results for placebo (4.0%).

The incidence of active and disordered type endometrial proliferation was less than 1% of participants treated with ospemifene. The vaginal bleeding incidence was similar in the treatment and placebo groups.

“This data tells me that this drug is clearly acting like its cousin raloxifene in the uterus, with virtually no active proliferation and no true hyperplasia. The FDA guidance for any of these products is less than 1% hyperplasia in 1 year, and there was a single case out of 342 biopsies, says Dr. Goldstein.

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