An epidemiological study of cancer in adult twins born in Norway 1905-1945

We have identified 23 334 individuals (40%) of twins born in Norway 1905-45 where both twins were alive in 1960 without malignant disease. These were linked to the Cancer Registry of Norway. A reduced risk of malignant diseas e was demonstrated among twins for all tumour sites combined; standardized incidence rate (SIR): 0.90 (95% CI 0.85-0.94) in females and 0.95 (95% CI 0 .90-0.99) in males. In both sexes, we observed a significant reduced incide nce of malignant melanomas of the skin. The incidence of colorectal cancer tended to be reduced for both sexes. In females, the incidence of tumours o f the central nervous system and lungs were reduced. We consider our findin gs are real, but cannot explain them. (C) 2001 Cancer Research Campaign.