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Two recent studies (Lichtenstein et al 2000, Risch 2001) have reached very different conclusions on the importance of genetics in cancer risk. These two papers form an important cautionary tale in that they both used the same data set (a very impressive 44,788 pairs from the Swedish, Danish, and Finnish twin registries), but reach very different conclusions.
Lictenstein et al (Environmental and heritable factors in the causation of cancer, New England Journal of Medicine 343: 78--85) concluded that most of cancer risk is environmental, as (using a threshold liability model, see Chapter 25) they estimated the heritability for the underlying liability for a number of cancers to be around 0.3, implying that only 30 percent of liability differences are due to genetic differences.
Risch (The genetic epidemiology of cancer" interpreting family and twin studies and their implications for molecular genetic approaches, Cancer epidemiology, Biomarkers and Prevention 10: 733--741), on the other hand, used familial risk ratios to examine the same data set, finding that the observed values were consistent with gene contributing significant risk for the various cancers.
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Bruce Walsh. email@example.com . Comments welcome.