Lactation and the risk of breast cancer in an Italian population.

The relation between breast feeding and breast cancer was investigated in a multicentric case-control study conducted in Italy on 2,167 parous women with histologically confirmed breast cancer, diagnosed within 1 year, and 2,208 parous control women admitted to hospitals in the same catchment areas of cases for acute, non-neoplastic, non-gynecological non-hormone-related diseases. Compared with women who had never tried to lactate, those who had always failed had a multivariate odds ratio (OR; adjusted for parity, education and several other potential confounding factors) of 0.94, and those who had lactated had an OR of 1.17. The multivariate ORs of women who had breast fed 1, 2 and 3 or more children were, respectively, 1.14, 1.18 and 1.32, compared with women who had never lactated. None of these ORs was statistically significant. Compared with women who had never breast fed, the multivariate ORs were 1.19 for women reporting less than 6 months of breast feeding, 1.15 for 6-11 months, 1.34 for 12-17 months, 1.10 for 18-23 months and 0.86 for 24 months or more. No appreciable difference was evident across strata of age, menopausal status, parity and age at first birth, while there was a hint of interaction with education. Our study therefore excluded any appreciable protective role for lactation in breast cancer risk, with the patterns of lactation in this European population, aside from the protective role of parity on breast carcinogenesis.