Ovarian cancer risk reduced with oral contraceptives
Breast cancer and colorectal cancer risks are not reduced by oral contraceptive use.
Long-term oral contraception use is correlated with a reduced risk of ovarian cancer and endometrial cancer across a variety of lifestyle variables, according to a study published in JAMA Oncology.
Kara A Michels, PhD, of the Division of Cancer Epidemiology and Genetics at the National Cancer Institute and National Institutes of Health in Maryland, and associates sought to determine if a correlation was present between oral contraceptive use and a decreased risk of certain cancers across difference lifestyles.
Main outcomes included diagnosis of ovarian, endometrial, breast, and colorectal cancers. Lifestyle measures included cigarette smoking, alcohol intake, body mass index (BMI), and exercise. Statistical adjustments were made for age at menarche, age at enrollment, and race.
The researchers used the prospective NIH-AARP Diet and Health Study participant data, which included more than 100,000 women who confirmed oral contraceptive use (median age, 62 years). Contraceptive use was categorized as 1 to 4 years (n=34,866), 5 to 9 years (n= 24,564), and 10 or more years (n=18,962), compared with nonusers (less than 1 year).
Women who used oral contraceptives for more than 10 years (long-term users) were more often younger, premenopausal, admitted to alcohol consumption, and had a reduced BMI, compared with nonusers, though 96% of the entire cohort was postmenopausal.
It was reported that women in the long-term cohort had a 40% reduced risk of ovarian cancer (hazard ratio [HR], 0.60) when compared with nonusers. Ovarian cancer risk was reduced by 30% in long-term users who were former smokers and 66% in current smokers.
A similar reduction trend (34%) was noted in endometrial cancer among long-term oral contraceptive users (HR, 0.66). Women with BMIs lower than 25 did not have a significant risk reduction. Women with BMIs higher than 30, current smokers, and those with minimal physical activity had the most robust risk reductions (HR; 0.36, 0.47, and 0.40, respectively). Breast cancer and colorectal cancer reductions were insignificant.
“If the primary mechanism of these medications is altering hormone metabolism, the associations between newer medications and cancer risk may differ for future cohorts,” the authors reported.
“Therefore, continued study of [oral contraceptive] use as primary prevention for cancer is warranted,” stated the investigators. “Ultimately, this study contributes to a body of literature that may enable clinicians to better counsel their patients about the risks and benefits of taking [oral contraceptives].”
- Michels KA, Pfeiffer RM, Brinton LA, Trabert B. Modification of the associations between duration of oral contraceptive use and ovarian, endometrial, breast, and colorectal cancers. JAMA Oncol. 2018 Jan 18. doi:10.1001/jamaoncol.2017.4942 [Epub ahead of print].