General epidemiology of breast cancer in Northern Italy

The role of the major identified risk factors for breast cancer was assessed using data from a hospital-based case-control study conducted in Northern Italy on 1108 women with histologically confirmed breast cancer and 1281 control subjects with a spectrum of acute conditions unrelated to any of the established or potential risk factors for breast disease. With reference to nulliparous women, the risk of breast cancer was below unity for those who first gave birth below age 25, and above unity for those with later first full-term pregnancy. However, in each stratum of age at first birth, the point estimate was below unity for women with five or more births. The relative risk for =5 births compared with 1 or 2 was 0.6 (95% confidence interval =0.4–0.9) when allowance was made for age at first birth. Likewise, there was a significant and independent effect of age at last birth which was evident in various strate of parity and age at first birth. The overall relative risk for last birth at 30 years or over compared with under 30 was 1.4 (95% confidence interval =1.1–1.8). There was little relation of breast cancer risk with abortions or miscarriages. Breast cancer cases reported earlier menarche and later menopause; further, lifelong irregularities in menstrual pattern were less common among the cases (relative risk=0.6, 95% confidence interval = 0.5–0.8). The risk estimates were elevated in women with positive history of benign breast disease, family history of breast cancer and greater body mass index. The latter trend in risk, however, was more evident in pre-than in post-menopausal women. Cases and controls were similar with reference to marital status, but age at first marriage was considerably higher among the cases, though this association disappeared after multivariate analysis, indicating that it was totally accounted for by other factors (i.e., age at first birth). The risk of breast cancer was unrelated to the interval between age at first marriage and age at first livebirth. Cases were more educated and of higher social class, and the effects of these indicators were not totally explainable in terms of differences in reproductive habits for various social classes, or other risk factors considered in this paper.