Inbreeding and cancer incidence in human isolates

This study investigates the incidence of cancer in isolate populations. Tho rough anthropological research over the past 3 decades has established isla nd populations in Middle Dalmatia, Croatia, as outstanding examples of gene tic isolates. The number of cancer cases on 5 islands (Brac, Hvar, Korcula, Vis, and Lastovo) over a 20-year period (1971-1990) has been extracted fro m the data of the Croatian Cancer Registry. The population of coastal Dalma tia, characterized by similar environmental factors but a different populat ion genetic structure, was used as a control population. The leading hypoth esis was that, if there were genes or gene complexes (especially with reces sive inheritance) responsible for genetic susceptibility to certain types o f cancer, then the incidence of those cancer types should be greater in rep roductively isolated island populations than in a control population becaus e of increased manifestation of such genes or gene complexes caused by inbr eeding. Furthermore, the cancer incidence should increase along with greate r reproductive isolation (i.e., greater geographic distance of the islands from the mainland). After adjusting the data for sex and age, I confirmed t he hypothesis: Island populations have greater total cancer incidence than the control population for both sexes. The excess incidence on the islands shows an almost linear correlation with geographic distance from the mainla nd. The cancer sites primarily responsible for the excess incidence are bla dder cancer in males, and breast, ovarian, brain, and large bowel cancer in females, predominantly in the younger age groups.