Breast cancer risk associated with reproductive factors and breast parenchymal patterns.

In a population-based study of 23,511 women 50-67 years of age at the time of first screening, a striking relationship was found between parity and age at first childbirth, on the one hand, and two radiologic aspects of breast parenchymal pattern (dysplasia and prominent duct pattern), on the other. These relationships appeared to be causal.