The association between induced and spontaneous abortion and risk of breast cancer in Slovenian women aged 25-54.

The risk of breast cancer may be increased by induced or spontaneous abortion. The evidence for this association was evaluated in a population based case-control study in Slovenia, where 624 women aged 25-54 years with breast cancer diagnosed during 1988-1990 were matched for age and site of residence with controls randomly selected from the Slovenian Population Registry. Odds ratios (OR) and 95% confidence intervals (CI) were obtained by conditional logistic regression analyses. Spontaneous abortion was not associated with a significantly increased risk of breast cancer (nulliparous women: OR=1.41, 95% CI 0.22-9.01; uniparous women: OR=0.98, 95% CI 0.50-1.91; women with parity 2 or more: OR=1.40, 95% CI 0.91-2.15). Induced abortion was not associated with a statistically significant elevated risk. The risk of breast cancer was higher in nulliparous women (OR=2.49, 95% Cl 0.68-9.09), and was less among women who had more deliveries. In uniparous women, the risk of breast cancer appeared higher when the induced abortion took place before a first full-term pregnancy (OR=1.94, 95% CI 0.70-5.39) rather than after a first full-term pregnancy (OR=1.22, 95% CI 0.71-2.10) but neither of these odds ratios reached significance. We found no significant association between spontaneous abortion or induced abortion and breast cancer risk. This study found an elevated, but not statistically significant, risk associated with induced abortion among nulliparous women and among parous women when the induced abortion was before the first full-term pregnancy.