Independent roles of various factors in the risk of breast cancer

A retrospective case-control study in Finland investigated the independent roles of various factors in the risk of breast cancer (BC). The study included all Finnish women who were diagnosed with a first breast cancer between 1^st January 1994 and 31^stDecember 2013. The study showed that pregnancy had a dual effecton BC risk, with a transient increase in risk followed by a long-term protective effect. As the number of children increased, the short-term excess risk was lower and the protective effect was observed earlier. Socioeconomic status and postmenopausal hormonal therapy had a large effect on BC risk, while occupational physical activity had only a small independent effect.