We have examined the association between induced or spontaneous abortion and breast cancer risk in Greece. In a hospital-based case-control study in Athens, 820 patients with confirmed breast cancer were compared with 795 orthopedic patient controls and 753 healthy visitor controls, matched to cases by age and interviewer. Logistic regression was used to analyze the data, controlling for demographic, reproductive and nutritional variables. Odds ratio (OR) patterns were similar for the 2 control series, which were therefore combined to increase precision of the estimates. The risk for breast cancer was not increased for women who had a history of abortion, compared to nulliparous women with no history of abortion. Thus ORs and 95% confidence intervals were for nulliparous women with spontaneous abortion, 1.17 (0.64-2.13); for nulliparous women with induced abortion, 0.98 (0.56-1.73); for parous women with no abortion, 0.56 (0.31-1.01); for parous women with spontaneous abortion, 0.61 (0.33-1.14) and for parous women with induced abortion, 0.99 (0.56-1.74). When the analysis was restricted to parous women, using parous women with no history of abortion as the baseline, ORs and 95% confidence intervals were for induced abortion before first full-term pregnancy, 2.06 (1.45-2.90); for induced abortion after first full-term pregnancy, 1.59 (1.24-2.04) and for spontaneous abortion, 1.10 (0.82-1.40). Our findings suggest that an interrupted pregnancy does not impart the long-term protective effect of a full-term pregnancy attributable to terminal differentiation.
PIP: The association between induced or spontaneous abortion and breast cancer risk is examined. In a hospital-based case-control study in Athens, Greece, during January 1989-December 1991, 820 patients with confirmed breast cancer were compared with 795 orthopedic patient controls and 753 healthy visitor controls, matched to cases by age and interviewer. Data analysis by logistic regression controlled for demographic, reproductive, and nutritional variables. Crude odds ratio (OR) patterns were similar for the 2 control series, which were therefore combined. The risk for breast cancer did not increase for women who had a history of abortion, compared to nulliparous women with no history of abortion, but it appeared to increase significantly with a history of induced abortion. Thus ORs and 95% confidence intervals were 1.17 (0.64-2.13) for nulliparous women with spontaneous abortion; 0.98 (0.56-1.73) for nulliparous women with induced abortion; 0.56 (0.31-1.01) for parous women with no abortion; 0.61 (0.33-1.14) for parous women with spontaneous abortion; and 0.99 (0.56-1.74) for parous women with induced abortion. Among parous women the protective effect of parity was all but removed with a history of induced abortion (OR = 0.99). When the analysis was restricted to parous women, using parous women with no history of abortion as the baseline, ORs and 95% confidence intervals were 2.06 (1.45-2.90) for induced abortion before first full-term pregnancy; 1.59 (1.24-2.04) for induced abortion after first full-term pregnancy; and 1.10 (0.82-1.40). It became evident that a history of induced abortion was associated with an increased risk for breast cancer. It appeared that an induced abortion before the first full-term pregnancy is associated with a more elevated risk than is an abortion after the first full-term pregnancy. An interrupted pregnancy does not seem to impart the long-term protective effect of a full-term pregnancy attributable to terminal differentiation of the mammary tissue, and the incomplete differentiation may render it more susceptible to carcinogenic agents.