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Oral contraceptives reduce risk for some cancers

The benefits of oral contraceptives outweigh the harms, protecting against lifetime risks of certain cancers, including endometrial, ovarian and colorectal cancer, according to research published in the American Journal of Obstetrics and Gynecology.

“Oral contraceptives have been used by hundreds of millions of women around the world,” Lisa Iversen, PhD, of the Institute of Applied Health Sciences at the University of Aberdeen in Scotland, and colleagues wrote. “Important questions remain regarding the very long-term cancer risks associated with oral contraception.”

To determine this association between lifetime cancer harms and oral contraceptive use, Iversen and colleagues analyzed the rates of all cancer types, as well as specific disease types, for ever and never users of combined oral contraceptives who participated in the 1968 to 1969 UK Royal College of General Practitioners’ Oral Contraception Study and continued follow-up care for up to 44 years (n = 46,022). These rates were standardized for age, parity, social class and smoking. Using Poisson regression adjustment for the same factors, the researchers estimated incidence rate ratios (IRR) between ever and never users and assessed effects by time since last oral contraceptive use.

Data showed that there were 4,661 ever users with at least one form of cancer and 2,341 never users with at least one form of cancer during 884,895 and 388,505 woman-years of observation, respectively. A reduction 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 0.5-0.89) and lymphatic and hematopoietic cancer (IRR = 0.74, 99% CI, 0.58-0.94) was associated with ever use of oral contraceptives. Lung cancer risk only increased in ever users who smoked at recruitment.

The study confirmed previous research showing an increased risk for breast and cervical cancer, however within approximately 5 years of discontinuing use of oral contraceptive, this increased risk appeared to be eradicated.

There was no evidence of either breast or cervical cancer recurring at increased risk in ever users and there was no association between new cancer risks emerging later in life and oral contraception, according to the researchers. Overall, there was a neutral balance of cancer risk among past users of oral contraceptives and the increased risks of breast cancer and cervical cancer were offset by the endometrial, ovarian and colorectal cancer benefits that persist for at least 30 years.

“Most women who choose to use oral contraceptives do not expose themselves to long-term cancer harms; instead many benefit from important reductions in some cancers which persist for many years after stopping,” Iversen and colleagues concluded. – by Alaina Tedesco

Disclosure: The researchers report receiving funding from the Royal College of General Practitioners, Medical Research Council, Imperial Cancer Research Fund, British Heart Foundation, Schering AG, Schering Health Care Ltd, Wyeth Ayerst International, Ortho Cilag and Searle.