Induced abortion as an independent risk factor for breast cancer: a systematic review and meta-analysis of studies on south asian women

Objective South Asia, a historically low-incidence region for breast cancer, has produced many recent studies examining reproductive factors. We compiled these studies to confirm the reality of the significant association reported in the first, 1996 review of induced abortion as a risk factor, independent of abortion's known effect in abrogating the protection afforded by full-term pregnancy. Methods We searched the medical literature for English language studies on breast cancer incidence in women in South Asia published from 1 January, 2000 through 30 June, 2017, using Pubmed, Scholar-Google, and bibliographic searches. Studies were included which reported overall data on induced abortion and/or abortion non-specifically. All 20 eligible studies were of retrospective, case-control design. Data from individual studies were combined using random effects modeling, following the determination of significant heterogeneity. Results Cumulative OR for all 20 studies was 2.51 (95%CI: 1.67-3.75) and 3.91 (95%CI: 1.02-14.97) for the five studies which reported specific data on induced abortion. Significant dose-dependence was observed among all 5 studies which stratified by number of abortions. Meta-regression of OR v. abortion prevalence among controls was statistically significant, as observed in a 2013 meta-analysis in China. Conclusion The moderately strong association identified between abortion and breast cancer explains in part the spread of the breast cancer epidemic to South Asia as it has become Westernized. Continuing denial of the abortion-breast cancer association can only ensure that the acknowledged worldwide breast cancer epidemic will continue to worsen, costing many millions of women their lives over the next several decades.