A record-based evaluation of induced abortion and breast cancer risk (United States)

Objective: Previous studies of induced abortion and breast cancer may have been limited by differential reporting of abortion history. We conducted a population-based case-control study to evaluate abortion (both induced and spontaneous) and breast cancer risk. Methods: All study subjects were aged 20-69 years and members of Group Heal th Cooperative of Puget Sound (GHC). Incident invasive breast cancer cases (n = 138) were identified from the linkage between the GHC enrollment file and the Seattle-Puget Sound SEER Cancer Registry. Controls (n = 252) were r andomly selected from GHC enrollment files and matched to cases on age and enrollment period. All subjects had to have been enrolled at GHC for the 2 years preceding diagnosis (cases) or reference (controls) date. The unified medical record of each case was abstracted for pregnancy history, includin g prior induced and spontaneous abortions, menopause status, height and wei ght, screening practices, and other risk factors. Results: Compared to all women who had never had an induced abortion, the m ultivariate adjusted relative risk of breast cancer in women with an induce d abortion was 0.9 (95% confidence interval 0.5-1.6). This risk was similar in parous women, and nulliparous women. There was no association between s pontaneous abortion and breast cancer risk. Conclusions: These results do not support a relation between induced aborti on and breast cancer incidence.