Introduction

Epidemiology is the study of the distribution, prevalence, and etiology of disease and for this book the disease is, of course, cancer. Epidemiology is studied both by observation and with experiments. This chapter is confined to observational investigations. Risk factors identified in epidemiological studies have the potential, if put to use, to prevent or lower the incidence of certain cancers. These studies include an examination of the effects of occupational exposure to carcinogens as well as lifestyle activities that tend to make certain individuals prone to cancer (lifestyle is examined in greater detail in the following chapter). A practical example, already widely recognized, relates to lung cancer and smoking. Lung cancer does not randomly afflict individuals within a population. Rather, it appears disproportionately in people who smoke cigarettes. Lung cancer differences in different groups can be, and is, correlated with different exposure to cigarette smoking. When smoking increased, so too did the incidence and deaths due to lung cancer. In the United States, smoking-induced lung cancer remains the greatest cause of death by malignancy for men and women (Figures 7–1 to 7–3; Color Plates 5 through 10). Identifying tobacco as a risk factor for lung cancer has, inherent with that knowledge, the potential for prevention of much of the disease.