Breast cancer risk factors in Italian women: a multicentric case-control study.

To evaluate the importance of several risk factors for breast cancer in the Italian female population, a large multicentric case-control study was conducted in 10 breast clinics in Italy. The study included 1,556 women affected by breast cancer, histologically and/or cytologically confirmed. Controls were 1,505 women admitted to a hospital in the same town, matched with cases for residence and with the same age distribution of the Italian female population. The risk factors considered in this study were family history of breast cancer, reproductive history, height and weight, use of oral contraceptives, other hormonal therapies and smoking history. The results of this study confirm the significant role of a positive family history of breast cancer (RR = 2.37); the relative risk was even higher when a first-degree relative was affected or the breast cancer was bilateral. The analysis of the reproductive history showed a significant trend of increasing risk with increasing age at first birth and, although less evident, with increasing number of children. Quetelet's index (kg/m-2) was positively correlated with breast cancer risk, mostly in postmenopausal women. Among other studied factors, only late age at menopause confirmed an increased risk for breast cancer, whereas age at menarche, use of oral contraceptives and smoking histories did not show any significant correlation with breast cancer risk. These results are in substantial agreement with other international studies, but represent an interesting contribution to studies about the Italian female population.