The etiology of female breast cancer

Considerable knowledge has been acquired abo ut the determinants of female breast cancer. A positive family history among first degree relatives is associated with an increased risk of breast cancer, as is a past history of benign proliferative breast disease. Risk increases with decreasing age at menarche, and with increasing age at first full term pregnancy and at menopause. Pregnancy is followed by a short-term increase in risk, followed by a long-term decrease. Risk increases with age. Evidence that environmental determinants are involved comes from the study of migrant populations: migrants assume the risk of breast cancer prevalent in their new environment, arguing against the hypothesis that risk is determined solely by genetic mechanisms. The best understood environmental determinant is ionizing radiation: it increases risk in a dose-dependent fashion. While ecologic studies of diet supported the hypothesis that high fat intake increases risk, cohort and case-control studies have yielded conflicting evidence, casting doubt on this hypothesis. However, weight gain during adult life is associated with an increased risk. Some drugs increase risk, specifically exogenous oestrogens and ethanol. The anti-oestrogen tamoxifen reduces risk. Recent evidence shows that both passive and active exposure to tobacco smoke is associated with an increased risk of breast cancer. Some women may be more susceptible to the effects of tobacco smoke on a genetic basis. Undoubtedly, other environmental determinants of breast cancer will be discovered. Copyright (C) 2000 S. Karger AG, Basel.