The variation in cancer incidence among various population groups has long suggested a role for the environmnet in cancer development. The environmental hypothesis is further supported by shifting cancer incidences in migrant populations whose rates tend to approximate those of their current host country, by geographic differences in cancer rates within the United States, by the changing incidence of certain cancers over time, by ethnic–socioeconomic differentials, and by the epidemiologic evidence linking risks to a variety of lifestyle and other environmental exposures. Not long ago, the role of inherited susceptibility in human cancer was considered to be quite small. However, recent progress in identifying and characterizing highly penetrant, but relatively rare, susceptibility genes has furthered our understanding of genetic mechanisms and their role in cancer etiology. Further, the common polymorphisms of modifier genes that confer low relative and absolute risks, but high population-attributable risks in the presence of relevant environmental exposures, are becoming increasingly important to the public health burden of cancer.

Many speakers discussed the evidence suggesting a role for the environment, for genes, and for their interactions. Cancers such as breast, lung, and colorectal, which were thought to lack an inherited component in the past, are being linked to a number of rare but highly penetrant mutated genes. As many speakers asserted, understanding and characterizing these genes will be an important area of research for the next decade. They further emphasized the need to combine epidemiologic techniques with molecular biology. Cancer involves changes in DNA. We will have to determine which changes are germline and which are somatic and how environmental influences alter the mechanisms of DNA repair and replication.

Some conference participants identified several strategies for reducing the future incidence of and death from cancer, the most critical being the reduction of tobacco use by all segments of the population, since smoking causes an estimated 30 percent of all cancer deaths. Another strategy suggested by some speakers would be to increase the use of effective but currently underutilized cancer screening tools. Yet other strategies identified include developing and applying state-of-the-art diagnostic tests and treatments, as well as identifying and reducing health disparities across diverse populations. Behavioral change, perhaps the most challenging, but potentially the most effective strategy, should be a central element of a successful cancer prevention program regardless of genetic predisposition to cancer, said several speakers.

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