Epidemiology, prevention, and early detection of breast cancer

Studies of the etiology, early detection, and prevention of breast cancer reported in the past year are reviewed in this paper. Studies of the etiology of breast cancer include reports on genetic and environmental factors. A major advance in the study of inherited forms of breast and ovarian cancer occurred with the identification of the BRCA1 gene. A second breast cancer susceptibility gene, the BRCA2 gene, was localized to chromosome 13q12-13. Multiple mutations in the BRCA1 gene have been identified, presenting a challenge for the development of predictive testing. Controversy continues over the association between hormone replacement therapy and the development of breast cancer. A study of exercise suggests a strong protective effect against the development of early onset breast cancer. Recent studies have failed to find a strong link between dietary fat intake and the development of breast cancer. A meta-analysis of studies of the efficacy of screening for the prevention of breast cancer mortality demonstrates a significant reduction in mortality among women 50 years of age and older. A lowering of breast cancer mortality for women aged 40 to 49 was only demonstrated after 10 to 12 years of follow-up. The risks and benefits of tamoxifen therapy, a potential breast cancer chemoprevention agent, continue to be clarified. Adverse effects on the endometrium, including an increased risk of endometrial cancer, have been reported. Beneficial effects include an improved cardiovascular risk profile and preservation of bone mineral density among postmenopausal women.