Differences between spontaneous and induced abortions as risk factors for breast cancer.

TL;DRAbstract

Recent epidemiologic studies have found that spontaneous abortion has no association with breast cancer, while induced abortion is associated with a moderately increased risk. Although this finding may, in part, reflect confounding and ascertainment bias, there are credible biologic reasons for a difference in risk between these two events. Experiments with rats have indicated that proliferated but not differentiated terminal duct and lobular cells increase the susceptibility of breast tissue to carcinogens. Since ductal and lobuloalveolar breast cells proliferate in the first two trimesters of pregnancy and differentiate in the third, it would follow that the later (up through the late second trimester) the pregnancy is terminated, the greater the risk. Although there is a trend toward induced abortion at earlier gestational ages, spontaneous abortion tends to be the earlier event. Even when induced and spontaneous abortions occur at the same gestational age, dead embryos or fetuses a

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