More than 10 years of oral contraceptive use appeared associated with significant reductions in risk for ovarian and endometrial cancers, according to data published in JAMA Oncology.
The association did not occur with breast or colorectal cancers.
For endometrial cancer, the researchers observed the greatest risk reductions among women who were smokers and obese, indicating they may be at risk for chronic diseases.
“In 2013, the Agency for Healthcare Research and Quality released a report on ‘Oral Contraceptive Use for the Primary Prevention of Ovarian Cancer,’ which synthesized the findings from published literature on [oral contraceptive] use and risks of several cancers,” Kara A. Michels, PhD, a postdoctoral fellow in the division of cancer epidemiology and genetics at NCI, and colleagues wrote. “Data gaps were identified, including a need to understand [oral contraceptive]-associated cancer risks in subpopulations, such as those stratified by smoking, obesity or family history of cancer.”
The researchers included data from 196,536 women (median age, 62 years; 91% white, 96% postmenopausal) from the NIH-AARP Diet and Health Study, which enrolled AARP participants from 1995 to 1996.
During follow-up through 2011, researchers identified 1,241 cases of ovarian cancer, 2,337 cases of endometrial cancer, 11,114 cases of breast cancer and 3,507 cases of colorectal cancer.
Researchers categorized length of oral contraceptive use as never or less than 1 year (n = 118,144), 1 to 4 years (n = 34,866), 5 to 9 years (n = 24,564), or more than 10 years (n = 18,962).
Researchers also assessed differences in associations relative to smoking status, alcohol consumption, BMI and physical activity.
Long-term (> 10 years) oral contraceptive use appeared associated with a lower risk for ovarian cancer (HR = 0.6; 95% CI, 0.47-0.76), and the association persisted across all modifiable lifestyle characteristics.
Long-term use also decreased risk for endometrial cancer (HR = 0.66; 95% CI, 0.56-0.78). This association appeared more pronounced among long-term birth control users who smoked (HR = 0.47; 95% CI, 0.25-0.88), had obesity (HR = 0.36; 95% CI, 0.25-0.52) and who exercised rarely (HR = 0.4; 95% CI, 0.29-0.56).
Associations between oral contraceptive use and breast cancer appeared primarily null; however, there were some trends toward an increased risk for cancer. Long-term oral contraceptive users who were current smokers had a 21% increased risk for breast cancer (HR = 1.21; 95% CI, 1.01-1.44). Long-term users who were moderate drinkers also had a slight increased risk for breast cancer (HR = 1.08; 95% CI, 1-1.17).
Researchers did not observe a significant association between duration of oral contraceptive use and colorectal cancer risk.
Study limitations included lack of adjustment for parity and no information on birth control formulation.
The study participants likely used early-generation drugs that contained higher doses of estradiol and progestins compared with new formulations.
“If the primary mechanism of these medications is altering hormone metabolism, the associations between new medications and cancer risk may differ for future cohorts. Therefore, continued study of [oral contraceptive] use as primary prevention for cancer is warranted,” the researchers wrote. – by Cassie Homer
Disclosures: The authors report no relevant financial disclosures.