Position Paper of the American Council on Science and Health on Risk Factors for Breast Cancer: Established, Speculated, and Unsupported

Abstract: This article provides the position of the American Council on Science and Health regarding how breast cancer is defined and classified; the magnitude of the public health problem of breast cancer among women; the implications of variation in incidence of breast cancer internationally and with migration; access to health care as a factor in slight differences in incidence and mortality rates among African-American and white women; and the evidence concerning various proposed human-breast-cancer risk factors. The article classifies risk factors as either established, speculated, or unsupported on the basis of available evidence. Specific genes have been identified that may explain as much as 5–10% of new breast cancer cases. Inherited predispositions may be characterized by family history of breast or ovarian cancer, young age at diagnosis, breast cancer diagnosed in both breasts, and male breast cancer. Benign breast disease (BBD), particularly the subtypes of BBD involving atypical hyperplasia, and exposure early in life to ionizing radiation is an established risk factor for breast cancer. Several reproductive characteristics are established as risk factors for breast cancer: early age at menarche, first full-term pregnancy after age 35 years of late age, and late age of menopause. Obesity and low physical activity are established as risk factors for breast cancer and are modifiable. Speculated risk factors for breast cancer that are gaining scientific support include nulliparity, oral contraceptive use, and postmenopausal estrogen replacement therapy. Speculated risk factors for which there is conflicting or preliminary support include not breast feeding, postmenopausal estrogen/progestogen replacement therapy, prescribed diethylstilbestrol, low consumption of phytoestrogens, specific dietary practices, alcohol consumption, not using nonsteroidal antinflammatory drugs, abortion, and breast augmentation. Unsupported risk factors include higher than average consumption of phytoestrogens, premenopausal obesity, electromagnetic fields, and low-dose ionizing radiation after 40 years of age. There is only limited support for xenoestrogens and large breast size as risk factors for breast cancer.