Oral Contraceptives May Reduce Endometrial Cancer Risk

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Longer oral birth control use among women is associated with a reduced risk of endometrial cancer, according to a study published in Lancet Oncology.  The study estimates that oral contraceptives have prevented 200,000 cases of endometrial cancer over the last 10 years.

For every 5 years of taking the pill, the risk of endometrial cancer decreased by 24% (P < .0001) and the risk reduction is maintained for more than 30 years after women stopped taking the pill.

The researchers performed estimates of endometrial cancer incidence rates for women in high-income countries. For women who never took oral contraception, an estimated 2.3 in every 100 would be diagnosed with endometrial cancer prior to the age of 75. The estimated rate among women who took oral contraception for 10 years would be 1.3 in every 100. And for women who took oral contraception for 15 years, it would be 1.0 in every 100.

The same decrease in risk was seen for women taking oral hormonal contraceptives in the 1960s through the 1980s, even though the level of estrogen in birth control pills in earlier decades was higher.

Prior studies have shown that oral contraceptives can decrease the risk of endometrial cancer while a woman is on the pill. But how long the effect lasts after stopping contraceptive use and what other factors influence risk have not been well studied.

The new analysis, by researchers from the Collaborative Group on Epidemiological Studies on Endometrial Cancer, suggests that the longer a woman stays on the pill, the greater the reduction in risk.

Valerie Beral, MD, professor of epidemiology at the University of Oxford in the United Kingdom, and study coauthors compiled data on 27,276 women with endometrial cancer and on 115,743 women who had no history of endometrial cancer to serve as a control group. The data was pooled from a total of 36 epidemiologic studies conducted in Europe, North America, Asia, Australia, and South Africa.

The risk reduction varied depending on the type of endometrial tumor. Risk reduction was strongest for carcinomas of the endometrial tissue-a 31% risk reduction compared with a 17% risk reduction for sarcomas (P = .02).

The proportion of risk reduction was similar despite differences in levels of body fat, use of alcohol, reproductive history, tobacco use, and ethnicity.

“Although this finding is impressive and instructive, the important clinical and public health question now is whether or not the available data allow women to optimally balance the benefits and harms of oral contraceptives,” wrote Nicolas Wentzensen, MD, PhD, and Amy Berrington de Gonzalez, DPhil, both of the division of cancer epidemiology at the National Cancer Institute in Bethesda, Maryland, in an accompanying commentary. Wentzensen and Berrington also noted that the question of whether oral contraceptives should be recommended for chemoprevention is still unclear.