Contributions of twin studies to cancer epidemiology

The use of twin studies in cancer epidemiology has facilitated the discovery of genetic and environmental risk factors that are difficult to investigate in singletons. This chapter summarizes twin studies that have provided unique contributions to cancer epidemiology. This research distinguished patterns of cancer occurrence in twins compared to singletons, estimated concordance and other parameters that provide insight into heritability, discovered risk factors by comparing cotwins, identified both consequences of screening behavior and long-term effects of cancer by comparing discordant twins, and demonstrated the phenomenon of twin to twin metastasis. Lastly, a novel methodological approach is introduced whereby studies of twins can be used to estimate genetic and non-genetic variation in epidemiologic risk of cancer as well as other diseases and conditions.