Early abortion and breast cancer risk among women under age 40.

In New York State, incidence of cancer and fetal death are reportable health events mandated by state law. These data enabled a population-based record linkage study of the effect of early pregnancy termination on breast cancer risk to be conducted. In upstate New York 1451 cases under age 40 were reported to the Cancer Registry during 1976-1980. Cases were matched with 1451 population controls by year of birth and by residence using zip codes. All names including those changed by marriage were matched with the reports of fetal deaths occurring between 1971 and 1980. Matched pairs analyses revealed an excess of early pregnancy terminations among cases in all categories. Odds ratios (OR) were significantly elevated among those with an induced abortion (OR = 1.9) and a spontaneous abortion (OR = 1.5). Elevated risks were also noted for consecutive abortion events without intervening livebirths.