An ounce of prevention is worth a pound of cure.” This well-known adage has become increas- ingly popular in relation to the prevention of cancer. Cairns (1975) has pointed out that more deaths from infectious disease have been prevented through measures such as vaccination, sani-tary engineering, and widespread education and immunization of the population than by thera- peutic measures, including the use of antibiotics. As our knowledge of the nature and causes of cancer increases, many individuals have proposed that cancer prevention can become a reality and be as effective as preventive programs against infectious diseases. One of the major bases for this proposal is the estimation, originally suggested by Higginson, Doll, and others (cf. Hig- ginson, 1979), that 80% to 90% of all human cancers are determined by environmental factors. This estimate was derived by comparing the worldwide high and low cancer death rates for indi- vidual neoplasms (Table 1.1). The lowest cancer death rate was considered to be due to inherent genetic and other “nonenvironmental factors,” with the difference between the lowest and the highest rates implicated as resulting from environmental agents. Even if the estimate were off by 100%, however, the environmentally induced cancers in the human would still be highly signifi- cant and, if prevented, could dramatically decrease the morbidity and mortality from cancer.
One of the major known environmental causes of cancer in the human is smoking (Chap- ter 1). Unfortunately we have not taken sufficient advantage of this knowledge to decrease the incidence of lung cancer, which is still increasing at a significant rate throughout the world. The determination of the myriad of other environmental factors important in the causation of cancer in the human is still a major problem. The most direct method for the determination of etiologi- cal factors in the causation of human cancer is the science of epidemiology. When epidemiolog- ical data are not available, scientists must rely on laboratory studies to aid in the determination of such etiological factors.