Abortion before first livebirth and risk of breast cancer.

The present study examined the association between abortion prior to a first livebirth and breast cancer risk among a cohort of 3,315 women who had been delivered of liveborn children between 1946 and 1965 in a group of private gynaecology practices in Connecticut and followed through 1980 for the incidence of cancer. Among women with one livebirth at the time of cohort identification, a spontaneous abortion before this livebirth was associated with a 3.5-fold increase in the risk of breast cancer. The elevation in risk was independent of some of the major risk factors of breast cancer and became more pronounced as the number of years since the abortion increased.