The endocrinology of breast cancer.

Endocrine studies relating to breast cancer are reviewed and the conclusion is reached that studies of hormone levels and hormone excretion to date are inconsistent and inadequate to explain the epidemiologic characteristics of the disease. A new paradigm termed the "estrogen window hypothesis" is introduced. Breast cancer risk is related to the duration of unopposed estrogen exposure during puberty and the early postmenarchial period and during the perimenopausal period. These two estrogen windows provide periods of maximum inducibility by environmental carcinogens. The hypothesis is supported by studies of the survivors of the atomic bomb blasts in Hiroshima and Nagasaki and of women having repeated fluoroscopy for management of tuberculosis. The hypothesis generates many testable conclusions. If verified, the hypothesis could lead to significant public health initiatives.