Abstract
Oral contraceptives may influence the risk of certain cancers. As part of the AHRQ Evidence Report, Oral Contraceptive Use for the Primary Prevention of Ovarian Cancer, we conducted a systematic review to estimate associations between oral contraceptive use and breast, cervical, colorectal, and endometrial cancer incidence. We searched PubMed, Embase, and Cochrane Database of Systematic Reviews. Study inclusion criteria were women taking oral contraceptives for contraception or ovarian cancer prevention; includes comparison group with no oral contraceptive use; study reports quantitative associations between oral contraceptive exposure and relevant cancers; controlled study or pooled patient-level meta-analyses; sample size for nonrandomized studies ≥100; peer-reviewed, English-language; published from January 1, 2000 forward. Random-effects meta-analyses were conducted by estimating pooled ORs with 95% confidence intervals (CIs). We included 44 breast, 12 cervical, 11 colorectal, and 9 endometrial cancers studies. Breast cancer incidence was slightly but significantly increased in users (OR, 1.08; CI, 1.00-1.17); results show a higher risk associated with more recent use of oral contraceptives. Risk of cervical cancer was increased with duration of oral contraceptive use in women with human papillomavirus infection; heterogeneity prevented meta-analysis. Colorectal cancer (OR, 0.86; CI, 0.79-0.95) and endometrial cancer incidences (OR, 0.57; CI, 0.43-0.77) were significantly reduced by oral contraceptive use. Compared with never use, ever use of oral contraceptives is significantly associated with decreases in colorectal and endometrial cancers and increases in breast cancers. Although elevated breast cancer risk was small, relatively high incidence of breast cancers means that oral contraceptives may contribute to a substantial number of cases.
Highlights
Oral contraceptives, the most common form of effective and reversible contraception in the United States [1], significantly decrease the personal and societal burdens associated with unintended or unwanted pregnancy [2, 3]
Of the 6,476 unique citations screened, we identified 44 studies relevant to breast, 12 to cervical, 11 to colorectal, and 9 to endometrial cancers (Fig. 1)
We did not identify any qualitative difference between breast, cervical, colorectal, or endometrial cancers and oral contraceptive use based on probable dates of exposure when examined by study recruitment date versus publication date
Summary
The most common form of effective and reversible contraception in the United States [1], significantly decrease the personal and societal burdens associated with unintended or unwanted pregnancy [2, 3]. Oral contraceptive use may promote or initiate tumors of the breast or cervix [12,13,14]. For breast cancer, these risks may be even greater for women at elevated risk due to family history of cancer or genetic mutation carrier status (e.g., BRCA1/2); results from studies are inconclusive [15, 16]. Oral contraceptive use has been associated with a greater risk of certain clinically challenging types of breast tumors [17]. A recent systematic review and meta-analysis supports a significant risk reduction for ovarian cancer incidence and mortality associated with the use of oral contraceptives [20]
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