Net effect of oral contraceptive use on the risk of cancer in women in the United States

Objective: To estimate by meta-analysis the risk of developing cancer of the breast, uterine cervix, endometrium, ovary, and liver from age 20-54 years in the United States in women using oral contraceptives (OCs) for 4, 8, or 12 years. Data Sources: Using pairs of terms (such as oral contraception and breast neoplasms), I searched for English-language literature on OC use and cancer published since 1980 and cited through July 1994 in the MEDLINE data base. Methods of Study Selection: I analyzed all epidemiologic studies reporting estimates of relative risk (RR) by duration and recency of OC use (79 independent studies in total). Data Extraction and Synthesis: Reported duration-specific and recency-specific estimates of RR, with the corresponding numbers of cases and controls or person-time at risk for cohort studies, were abstracted from each article. Relative risk of cancer as a function of both duration and recency of OC use was then estimated by weighted regression and applied, using life-table methods, to United States population-based data on age-specific mortality and cancer incidence. Conclusions: For every 100,000 women in the United States who never use DCs, the number developing cancer from age 20–54 years is estimated to be 2782 (breast), 425 (cervix), 438 (endometrium), 369 (ovary), and 20 (liver). For women using OCs for 8 years, the estimated number of additional or fewer cases per 100,000 users is +151 (breast), +125 (cervix), −197 (endometrium), −193 (ovary), and +41 (liver). Therefore, from a population perspective, there are only small cancerrelated risks and benefits associated with OC use and, on balance, the net effect is negligible.