Oral birth control pills may protect women from ovarian and endometrial cancer even after decades, says study
Taking oral contraceptives protect women against ovarian and endometrial cancer and the protective effect remains for several decades after discontinuing the use, reveals analysis involving more than 250,000 women. According to a research team from Uppsala University, the results will enable women and physicians to make more informed decisions considering oral contraceptive use, thus constituting an important step towards personalized medicine.
The findings, published in Cancer Research, suggest that the protective association for ovarian and endometrial cancer remained significant up to 35 years after women stopped using oral contraceptives.
“It was clear that women who had used oral contraceptive pills had a much lower risk of developing both ovarian and endometrial cancer. Fifteen years after discontinuing oral contraceptives, the risk was about 50% lower. However, a decreased risk was still detected up to 30-35 years after discontinuation,” says corresponding author Åsa Johansson from the Department of Immunology, Genetics, and Pathology at Uppsala University, Sweden.
There are multiple methods of birth control. Combined oral contraceptives, also called “the pill”, contain the hormones estrogen and progestin and it is prescribed by a doctor. A pill is taken at the same time each day.
Unlike the combined pill, the progestin-only pill (sometimes called the mini-pill) only has one hormone, progestin, instead of both estrogen and progestin. This is also prescribed by a doctor and is taken at the same time each day. In both cases, the typical use failure rate is 7%, according to the US Centers for Disease Control and Prevention (CDC).
How common are these cancers in the US?
According to the National Cancer Institute, an estimated 21,750 Americans will have ovarian cancer in 2020 and 13,940 are projected to die from the disease this year. Approximately 1.2% of women will be diagnosed with ovarian cancer at some point during their lifetime, based on 2015-2017 data. In 2017, an estimated 233,364 women were living with ovarian cancer in the US.
“Ovarian cancer ranks fifth in cancer deaths among women, accounting for more deaths than any other cancer of the female reproductive system. About half of the women who are diagnosed with ovarian cancer are 63 years or older. It is more common in White women than African-American women,” explains the American Cancer Society.
Cancer of the endometrium (the lining of the uterus) is the most common cancer of the female reproductive organs, says the American Cancer Society. Endometrial cancer affects mainly postmenopausal women. The average age of women diagnosed with endometrial cancer is 60, and it is not common in women under the age of 45.
“About 65,620 new cases of cancer of the body of the uterus (uterine body or corpus) will be diagnosed in 2020. About 12,590 women will die from cancers of the uterine body. This cancer is slightly more common in White women, but Black women are more likely to die from it,” suggest experts.
The study includes women born between 1939 and 1970. “We performed an observational study in 256,661 women from UK Biobank. Oral contraceptives have now been available for about 60 years, giving us the opportunity to estimate their long-term risks and benefits. A large number of women in our study, who used oral contraceptives early in their reproductive years, are now reaching the age when the risk of breast, ovarian and endometrial cancer is peaking and our study can therefore give new leads on lifetime cancer risk,” researchers explain.
Of these, 210,443 (82%) had used or were still using oral contraceptives and were designated as ever users, while 46,218 (18 %) had never used oral contraceptives and were designated as never users. Among ever users, 4,659 women reported being current users.
The total number of cancer cases identified in the study was 17,739 (6.9%), 1,966 (0.76%), 16 and 2,462 (0.96%) for breast, ovarian and endometrial cancer, respectively.
“Cumulative risk of cancer over the timespan of the study, as measured by the odds ratio 8 (OR), and instantaneous risk, as measured by the hazard ratio (HR), were assessed. The odds for developing ovarian and endometrial cancer, OR: 0.72 and OR: 0.68 respectively, were lower among ever compared to never users. Given the body of evidence presented in our study, we argue that oral contraceptives can dramatically reduce women’s risk of ovarian and endometrial cancer,” investigators emphasize.
Oral contraceptive pills have previously been associated with a higher risk of breast cancer. In the current report, the team only found a small increased risk of breast cancer among oral contraceptive users, and the increased risk disappeared within a few years after discontinuation. According to them, the results are important, since oral contraceptive use has commonly been associated with side effects such as deep vein thrombosis and breast cancer.
“Our results suggest that the lifetime risk of breast cancer might not differ between ever and never users, even if there is an increased short-term risk,” says Johansson.
Experts recommend that given the large number of women currently using oral contraceptives, it is essential to understand both short, and long-term effects of exposure. “A deeper knowledge will enable both women and physicians to make more informed decisions with regards to oral contraceptive use. Decisions may also be based on a woman’s individual risk factors or on family and previous history of cancers,” conclude authors.