In 1981 Doll and Peto examined the degree to which cancer incidence and mortality rates could be reduced in the United States. Their approach did not attempt to project the level of reduction in the rate of mortality from cancer within a defined time frame. Rather, Doll and Peto estimated the reduction theoretically possible by comparing the rates in the United States with those in other countries. Their choice of method stemmed from the observation that the cancer incidence rate among migrants tends to be that found in the country to which they migrated, indicating that differential cancer incidence rates are due in part to environmental factors such as diet, exercise, occupational exposures, and smoking habits, and that cancer does not arise exclusively because of genetic factors.
Doll and Peto included in their estimates only information for people who were younger than age 65 because data on the incidence of cancer among older individuals were considered unreliable. Furthermore, they omitted cases of nonmelanoma skin cancers from their analysis because data on the incidence of these cancers were unreliable and also because these cancers are easily treated and are rarely fatal. Doll and Peto’s analysis was conducted by comparing the site-specific cancer incidence rates among male and female residents in Connecticut (the most complete U.S. cancer registry at that time) with the lowest reliable international site-specific cancer incidence rates available. Age-adjusted rates were collected from 1968 to 1972 from registries selected by the International Agency for Research on Cancer (IARC) (International Agency for Research on Cancer, 1976). The analysis used data from the United Kingdom, New Mexico, Japan, East Germany, Norway, Israel, Nigeria, Iowa, Puerto Rico, Finland, and New Zealand. The results of the analysis suggested that in 1970, 75 to 80 percent of all cancers in the United States could have theoretically been avoided if the population of the United States could be like that of the countries with the lowest incidences. This figure of 75 to 80 percent can thus be thought of as a crude estimate of the proportion of cancer in the United States that was (in 1970) due to “environmental” factors that made the U.S. population different from low-risk populations. The “environmental” factors that differ between the United States and low-risk populations are many and diverse and include birth weight; age at puberty; and lifelong patterns of tobacco use, diet, physical activity, alcohol consumption, use of pharmacological agents, and reproduction.
Of course, the more traditional and limited definition of “environmental” exposure fits in here, as the U.S. population and the populations of other countries also experience different levels of exposure to contaminants in air, water, and food. Occupational and environmental exposures are