The Windows of Susceptibility to Breast Cancer

Abstract

The occurrence of cancer of the breast has long been known [1–4] and the disease affects women of all races and nationalities and the incidence of has increased 30–40 % since the 1970s [2, 4–7]. This already dismal picture is worsened by the gradual increase in breast cancer incidence in most Western countries and in societies that recently became westernized or that are in the process of westernization [8, 9]. Epidemiological observations that daughters of women who migrate from low-incidence to high-incidence countries acquire the breast cancer risk prevailing in the new country [10], suggest that aspects of lifestyle or the environment are major determinants of breast cancer risk. A study of population-attributable risks has estimated that at least 45 % to 55 % of breast cancer cases in the United States may be explained by the following factors: advanced age at the time of the first full-term pregnancy, nulliparity, family history of breast cancer, higher socioeconomic status, earlier age at menarche, and prior benign breast disease [11]. Other statistical models appear to explain an even higher proportion of breast cancer on the basis of known risk factors [12]. Studies of atomic bomb survivors have shown that environmental exposures, such as ionizing radiation, are a risk factor for breast cancer [13]. Exposure to radiation at a young age (Fig. 1.1) has been identified as a causative agent of breast cancer in selected populations [14–17], but there is no definitive proof of what causes breast cancer in the population at large. The increased risk associated with exposure to environmental chemicals, such as alcohol [18] and cigarette smoke [19–25], makes these agents suspects for causing cancer in the human population (Fig. 1.1).