HEREDITARY FACTORS IN BASAL-CELL CARCINOMA OF THE SKIN - A POPULATION-BASED COHORT STUDY IN TWINS

The contribution of hereditary factors in basal cell carcinoma of the skin has not been well defined at the population level, We aimed to as sess the hereditary component in basal cell carcinoma by comparing its occurrence in monozygotic and dizygotic twin pairs. The Finnish Twin Cohort, comprising 12 941 adult, like-sex twin pairs with established zygosity and resident in Finland in 1975, was linked with the Finnish Cancer Registry. We identified 335 twin pairs in which at least one tw in had basal cell carcinoma diagnosed between 1953 and 1996, Standardi zed incidence ratios, concordances, tetrachoric correlations and pairw ise relative risks were computed by standard methods. Components of va riance in liability were estimated by structural equation modelling. T here was an elevated risk of basal cell carcinoma for the co-twin of a diseased twin, but no difference in risk by zygosity. During the pros pective follow-up in 1976-96, the probandwise concordance was 7.7% in monozygotic and 7.0% in dizygotic pairs. Model fitting indicated that genetic factors were not needed to account for the distribution of bas al cell carcinoma in twin pairs. These results confirm the major role of environmental factors in the aetiology of basal cell carcinoma.