Study: Birth Control Pills Provide Long-Term Cancer Prevention Benefits

New research is reiterating oral contraception is more than just a helpful family planning tool. Scientists are studying the pill's preventative effects against some types of cancer—and on the flip side, the link between hormonal contraceptives and risk of breast cancer.

A December study, published in Cancer Research, looked at not only the associations between oral contraception and breast, ovarian, and endometrial cancers, but also how long certain risk factors last.

Researchers at the University of Uppsala in Sweden looked at health data from over 250,000 women born between 1939 and 1970 in Britain to compare the incidence of breast, ovarian, and endometrial cancers between those that had never used birth control pills and those who had. About 80% of the study participants used oral contraceptives, on average for about ten years (ranging from one to 48 years of usage).

The scientists found women who had used oral contraceptives had a 32% reduced risk for endometrial cancer and a 28% reduced risk for ovarian cancer compared with those who had not used them. The data also showed the protective association remained significant for several decades—up to 35 years—after women stopped using the medications.

“The findings of the study, that use of oral contraceptives is protective of endometrial and ovarian cancer, is in line with previously published data,” Marina Stasenko, MD, a gynecologic oncologist at NYU Langone’s Perlmutter Cancer Center, tells Verywell. “However, the additional information that the risk reduction lasts 35 years after discontinuation is novel and rather exciting.”

How Does It Work?

Combination oral contraceptives include estrogen and progestin, which are synthetic forms of female sex hormones. The estrogen and progestin in oral contraceptives prevent ovulation and therefore protect against pregnancy.

While the study only found an association between the pill and reduced risk of cancer, experts theorize that the suppression of ovulation that birth control pills provide may be the mechanism at work here.

“If you’re not making those follicles every month or those eggs every month and you’re not getting that denuding of the surface of the ovary, then you’re less likely to have as much cell turn over and less opportunity for these cells to turn into cancer over time,” Joshua Cohen, MD, assistant professor of gynecology oncology at the UCLA Jonsson Comprehensive Cancer Center in California, tells Verywell.

Researchers believe that birth control may help prevent endometrial cancer—an estrogen-driven disease—by providing a continuous level of both estrogen and progesterone hormones in patients that don’t have regular cycles.

“In the beginning of a cycle you have a surge of estrogen, which is what stimulates the lining of the uterus and then after ovulation, the second hormone comes up—progesterone—and that’s what allows menses to take place,” Konstantin Zakashansky, MD, director of gynecologic oncology at Mount Sinai West in New York, tells Verywell.

If you’re not ovulating consistently and have continuous estrogen production without a counter effect of progesterone (which prevents this continuous proliferation) you're at a higher risk for developing hypoplasia, a precancer of the uterus, or cancer itself, Zakashansky explains.

Breast Cancer Risk

Since breast cancer is a hormonally-driven disease, experts say that taking external hormones, like oral contraceptives, can potentially drive certain types of breast cancer to proliferate, divide, and grow.

This may be one explanation for why some large studies have shown a link between birth control pills and an increased risk of breast cancer. Those risks were small and decreased after the use of oral contraceptives stopped.

Similarly, the current Swedish study found taking oral contraceptives led to a slightly increased risk of breast cancer. Those higher odds among current and recent users also started to decrease around eight years after they stopped taking the pill.

“Interestingly, the authors initially did see a small, short term increase in breast cancer risk, but that risk quickly went back to population baseline after participants discontinued the medication,” Stasenko says.

Zakashansky says the decision to take oral contraceptives, despite this risk, is a personal decision that must be made at the individual level with the guidance of doctors.

“You really have to talk to each individual patient and think about the individual risk, predisposition, and comorbidity and the benefit may outweigh the risk,” he says.

Screening For Cancer

During the current COVID-19 pandemic, it may seem more difficult to keep up with your annual doctor visits, but Cohen and other physicians stress that it’s even more important than ever for people to talk to their doctor and screen for cancer.

“No matter what type of doctor your seeing, you should describe feelings that you’re having, sensations in your body that you're worried about, and share your family history,” Cohen says. “We talk about breast self-awareness, which means knowing what’s normal for you as far as the symmetry or lumps and bumps. Those are things that are really important because for the general population that’s really what we’re going to offer for younger women.”

The United States Preventive Services Task Force (USPSTF) recommends that women who are 50 to 74 years old and are at average risk for breast cancer get a mammogram every two years.

The USPSTF does not recommend routine screening for ovarian cancer as its symptoms (abdominal pain, bloating, constipation, urinary symptoms, back pain, or fatigue) can be seen in both healthy women and women with late-stage ovarian cancer.

While endometrial cancer can cause symptoms like vaginal bleeding and is usually found at an early stage, there is no standard screening test currently available. However, researchers are performing clinical trials to explore the use case for several potential tests, like transvaginal ultrasound, a pap test, and endometrial sampling (biopsy).