Twin Studies and Other Genetical Investigations in the Danish Cancer Registry
League, and working in close collaboration with the National Health Service, is an organization with the primary intention to register all cancer cases, for resbarch purposes. This is done through a voluntary system ; all hospitals noti.y their cancer cases to the registry, and these notifications are supplemented with death certificates for all persons who are known to have suffered from malignant diseases, including leukaemias, myelomata and brain tumours. From Clemmesen's studies on occupational mortality from cancer in Denmark it was clear, already before the start of the Registry, that a complete investigation of the occurrence of cancer demAnded at least an estimation of the role played by heredity in the origin of various cancers. It-was thought to be especially valuable to carry out such an investigation alongside the mapping out of cancer incidence with regard to age, occupation, and other variables, and to compare the hereditary tendency shown by cancers of various sites in the same population and at the same time.