Smoking (active and passive) and breast cancer: epidemiologic evidence up to June 2001.

The first generation of studies evaluating the association between exposure to tobacco smoke and breast cancer merely compared active to nonactive smokers, with varying degrees of detail in the definition of active smoking. With rare exceptions, studies of this kind failed to show an effect of smoking on breast cancer risk. However, such analysis is probably insufficient. The most recent reports on the smoking-breast cancer connection have two characteristics. Some have separated women exposed to passive smoking from those nonexposed to either active or passive smoke. Other reports have focused on factors that modify the effect of smoking on breast cancer incidence, such as genetic markers or hormone receptors. A minority of reports combines these two characteristics. This review addresses the epidemiologic evidence for a link between smoking and breast cancer and discusses the implications of this evidence for future studies.