Women who take birth control pills may be protecting themselves against endometrial cancer – and not just during the years that they use these medications, but in the long term, according to an international study published in The Lancet Oncology.
The analysis revealed that every five years of oral contraceptive use reduced the risk of endometrial cancer by about a quarter, and the reduction of risk persisted for more than 30 years after the women had stopped using the contraceptive agent. In high-income countries, 10 years of oral contraceptive use reduces the risk of developing endometrial cancer before age 75 years from 2.3 to 1.3 cases per 100 users, the authors found. However, the risk reduction varied by tumor type — it was stronger for carcinomas than sarcomas.
The incidence of endometrial cancer is rare in women younger than 45 years of age, but the risk of disease increases in women 55 years and older. The American Cancer Society estimates that more than 10,000 women will die of uterine cancers in the United States in 2015.
According to the study’s authors, about 400,000 cases of endometrial cancer in women 75 years or younger may have been prevented in developed nations — as a result of oral contraception — during the period between 1965 and 2014, 50 percent of that in the last decade.
“The strong protective effect of oral contraceptives against endometrial cancer — which persists for decades after stopping the pill — means that women who use it when they are in their 20s or even younger continue to benefit into their 50s and older, when cancer becomes more common,” explained study author Valerie Beral, a professor at the University of Oxford, in a press release.
She added, “Previous research has shown that the pill also protects against ovarian cancer. People used to worry that the pill might cause cancer, but in the long term the pill reduces the risk of getting cancer.”
In conducting the study, the researchers combined data on 27,276 women with endometrial cancer from 36 epidemiological studies from North America, Europe, Asia, Australia and South Africa. The median age of the women was 63 years and the median year of diagnosis was 2001. While 35 percent of the 27,276 women reported using oral contraception for a median of three years, 39 percent of the more than 115,500 women in the control arm of the study had used oral contraceptives for a median duration of 4.4 years.
Despite the fact that estrogen levels in pills in the early decades were double those in contraceptive pills manufactured today, the reduction in risk was comparable, which suggests that the amount of hormones in the lower-dose pills is still sufficient to reduce the incidence of endometrial cancer, according to the authors.
The proportional risk reduction did not vary substantially by women’s reproductive history, adiposity (amount of body fat), alcohol use, tobacco use or ethnicity.