Oral contraceptive use confers long-term cancer protection

New findings from a cohort study with more than 4 decades of follow-up show that, while women who have ever used combined oral contraceptives see an increased risk of breast and cervical cancer, the risk disappears within about 5 years after stopping, but a protective effect against colorectal, endometrial, and ovarian cancer persists for more than 30 years.

The findings provide an update to the General Practitioners’ Oral Contraception Study of a United Kingdom cohort recruited in the late 1960s.

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Lisa Iversen, PhD, of the University of Aberdeen, Scotland, led the analysis, which looked at data from more than 35,000 women (from an original cohort of 46,000) and identified 4,661 ever-users of combined oral contraception who had at least one cancer during more than 884,000 woman-years of observation, and 2,341 women who had never used combined OCs but who had at least one cancer during more than 388,000 years of observation (Am J Obstet Gynecol. 2017 Feb 8. doi: 10.1016/ j.ajog.2017.02.002).

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The mean age was 70.2 years, most were white, and the mean follow-up was 40.7 years. Women who had used the pill did so a mean 3.66 years and used older, higher-estrogen formulations.

Compared with never users, users of oral contraception had a nonsignificant 4% reduced risk of any cancer. The incidence rate ratio for breast cancer was similar between ever users and nonusers (IRR 1.04; 99% CI, 0.91-1.17). Women who had used OCs saw significant reductions in colorectal (IRR, 0.81; 99% CI, 0.66-0.99), endometrial (IRR, 0.66; 99% CI, 0.48-0.89), ovarian (IRR, 0.67; 99% CI, 0.50-0.89), and lymphatic and hematopoietic cancers (IRR, 0.74; 0.58-0.94), compared with never users.

Lung cancer incidence was increased among ever users of OCs, but only in women who smoked at the time of recruitment.

“There was no evidence of new cancer risks appearing later in life among women who had used oral contraceptives,” the researchers wrote. “Thus, the overall balance of cancer risk among past users of oral contraceptives was neutral with the increased risks counterbalanced by the endometrial, ovarian, and colorectal cancer benefits that persist at least 30 years.”

The results, the researchers wrote, “provide strong evidence that most women do not expose themselves to long-term cancer harm if they choose to use oral contraception, indeed many are likely to be protected.”

The study was funded by the Royal College of General Practitioners, Medical Research Council, Imperial Cancer Research Fund, British Heart Foundation, Schering AG, Schering Health Care, Wyeth Ayerst International, Ortho Cilag, and Searle. The researchers reported having no conflicts of interest.