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32 Issues L. & Med. 325 (2017)
Abortion-Breast Cancer Link (ABC Link): Review of Recent Evidence from Asia

handle is hein.journals/ilmed32 and id is 331 raw text is: Abortion-Breast Cancer Link (ABC Link): Review of Recent Evidence from Asia Joel Brind, Ph.D. The first published evidence for the ABC link came from Asia 60 years ago. That's when a nationwide study in Japan showed a relative risk of 2.6; a 160% increase in breast cancer risk among women who'd had at least one induced abortion.' My group's Comprehensive Review and Meta-analysis of worldwide data,2 published by the British Medical Association in 1996, reported an average relative risk of 1.3 (30% increased risk. The difference in magnitude of the relative risk is traceable to the difference between a risk-increasing exposure (e.g., abortion) acting in a low breast cancer incidence pop- ulation (e.g., 20th century Japan), and a high incidence population (e.g., the Western industrialized world since the 1980s). In round figures, induced abortion adds about a 3% absolute lifetime risk to women everywhere. In the West, a relative risk of 1.3 raises the lifetime risk from about 10% to about 13%, and in the developing world, from about 2% to about 5%. Over the last 10 years, 20 studies have reported data on the ABC link in South Asian women (i.e., from India, Pakistan, Bangladesh and Sri Lanka).3 South Asia is a region wherein the typical woman marries while in her teens, begins having children early, has several of them, breastfeeds all of them, doesn't smoke and doesn't drink alcohol. Hence, contraceptive steroids and abortions are the only exposures among classical risk factors at play Breast cancer incidence is therefore low (about 2% cumulative lifetime risk), and a relative risk for abortion would need to be about five-fold higher in such a population (as in Japan in the 1950s) to show the same effect as in the Western world. The low magnitude of the risk identified worldwide led to the hypothesis that it was an artifact due to reporting or response bias,4 and that any real risk increase would have to show up in prospective data-based studies. The response bias hypothesis pos- tulates that in the collection of retrospective data for a case-control study, women who have breast cancer will be more likely to disclose prior abortions, compared to healthy women. Hence, the same prevalence of abortion in case and control groups, but a high- er reported prevalence among cases, would show up as an artificially positive-rather than a null-association. It is unarguable that a study based on prospective data is not subject to reporting bias, since ascertainment of exposure status (abortion) necessarily