New Study Adds to Evidence of Link Between Hormone Therapy, Ovarian Cancer Risk

July 21, 2009

A study in the current issue of JAMA attempts to assess the risk of ovarian cancer in women taking hormone replacement therapy (HRT, or “HT” in this study). The study (see abstract) adds to a growing body of literature suggesting that HRT may increase the risk of ovarian cancer.

Data for the current study comes from Danish Sex Hormone Register Study, which “follows a national cohort of Danish women aged 15 through 79 years to explore the influence of sex hormones on the risk of cardiovascular diseases and different female cancers.” That data was studied in conjunction with other national registries on cancers, hospital discharge and surgical data, demographics, and other details.

The final analysis included almost 910 thousand women who were 50 or older in 1995, had no previous cancers, and had not had their ovaries removed. The women were followed over time and those who had never used hormone replacement therapy were compared to those who had various types of HRT for ovarian cancer outcomes (previous research had suggested different outcomes depending on factors such as duration and type of HRT).

The findings are presented in terms of relative risk, meaning that the “RR” figures for those who used HRT reflect the amount of risk of ovarian cancer relative to those who never used HRT. The authors found that current users of hormone therapy had an increased relative risk of ovarian cancer of 1.38 (95% CI, 1.26-1.51) – or 1.38 times the risk of never-users. Risk for epithelial ovarian cancer (the most common type, which begins on the surface of the ovary) was increased for up to 2 years after ending hormone use, and declined to a similar level of risk as nonusers thereafter.

The authors did not find a significant difference in the rate of increased risk between estrogen-only or estrogen-plus-progestin users, between cyclic or continuous regimens, between oral vs. transdermal administration, or between different lengths of duration of use.

The authors note that their finding is somewhat different from previous similar studies, in that it “contrasts some prior studies that were not able to detect increased risk with HT of less than 5 years” and “no consistent association was found between increasing dose of ET (estrogen therapy) and the risk of ovarian cancer.”

They indicate that their findings are in accordance with some past studies (specifically the the Million Women Study and the Nurses’ Health Study) in that “past users users had only a slightly increased risk of ovarian cancer, and the excess risk was not apparent 2 years after cessation.” The authors also note that although the absolute risk increase is small, “ovarian cancer remains highly fatal, so accordingly this risk warrants consideration when deciding whether to use HT.”

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