Birth Control Duration Influenced Ovarian, Endometrial Cancer Risk

Use of oral contraceptives may be beneficial for chemoprevention for a range of women with different baseline cancer risks, according to the results of a study published today in JAMA Oncology. Specifically, long-term oral contraceptive use was associated with a decreased risk for ovarian cancer among women at risk for chronic diseases.

Results of the study may differ with the use of newer oral contraceptives, which have lower doses of estradiol and progestins than those used by the women in the study. Because of that, “continued study of oral contraceptive use as primary prevention for cancer is warranted,” wrote authors led by Kara A. Michels, PhD, of the division of cancer epidemiology and genetics at the National Cancer Institute in Bethesda, Maryland.

The influence of oral contraceptive use on cancer risk is not well understood. In this study, Michels and colleagues wanted to determine whether associations between duration of oral contraceptive use and risk for specific cancers were modified by lifestyle characteristics such as obesity or smoking status.

The researchers used data from more than 100,000 women who reported oral contraceptive use upon enrollment in the prospective NIH-AARP Diet and Health Study. Among these women, 1,241 had ovarian cancer, 2,337 had endometrial cancer, 11,114 had breast cancer, and 3,507 had colorectal cancer. The majority of women were white and postmenopausal.

“We did not have information on recency of oral contraceptive use or oral contraceptive formulation, but our participants were likely using first- and second-generation drugs (marketed before 1989); these drugs contained higher doses of estradiol and progestins with more androgenic activity compared with newer oral contraceptives,” the researchers wrote.

The researchers classified women as having never use or less than 1 year of use (reference group), 1 to 4 years of use, 5 to 9 years of use, or 10 or more years of use. For ovarian cancer, risk reductions seen with oral contraceptive use were strengthened with a longer duration of use (10 years or longer, hazard ratio [HR], 0.60; 95% CI, 0.47–0.76; P < .001). These risk reductions were similar across modifiable lifestyle factors.

Risk reductions for endometrial cancer were also strengthened with increased duration of use (long-term use HR, 0.66; 95% CI, 0.56–0.78; P < .001). Women who were smokers (HR, 0.47), had an obese body mass index (HR, 0.36), and who exercised rarely (HR, 0.40) had the most pronounced reductions in risk for endometrial cancer.

No associations between oral contraceptive use and risk for breast or colorectal cancer were identified.

“Oral contraceptives may influence carcinogenesis as a result of the decreased production of and exposure to estradiol across the menstrual cycle-a consequence of the continuous progestin dose provided by oral contraceptives,” the researchers wrote. “These medications may actually influence long-term changes in hormone metabolism.”