Etiology of breast cancer. II. Epidemiologic aspects.

The epidemiology of breast cancer is reviewed with particular emphasis on its etiology. A number of studies suggest that differences in breast cancer incidence are associated with differences in marital status, number of pregnancies, age at menarche, age at menopause, height and weight, socioeconomic status, geographic location and residence. However, in no case is the evidence adequate to establish a "cause and effect" relationship. The genetic component of these associations may be of primary importance, while other conditions such as marital status are probably indirect reflections of the operation of more fundamental factors.There is a general consensus that endocrine factors play an important part in mammary cancer occurrence. At present, the association between breast cancer and the presence of the virus-like (type B) particles in human milk is not established.