Genes, Hormones, and Pathways to Breast Cancer

Much current epidemiologic research aims to find the factors that trigger the development of breast cancer in women who are genetically predisposed to it. In this issue of the Journal, Hamilton and Mack1 add to that rapidly growing literature some intriguing observations from a study of female twins. They find evidence that hormonal exposures at puberty may play an exaggerated part in some women who are likely to be at high genetic risk for breast cancer, even though the responsible genes are unknown. On the basis of a multifaceted examination of different risk factors in various groups of twins, they . . .