Risk of cancer in an inbred population

Background: In spite of a high prevalence of consanguineous marriages in Asia and Africa, there has been little epidemiological research on the effect of inbreeding on cancer risk. Methods: We conducted a case–control study of 391 native Arabs with cancer and 378 matched healthy controls. All cases had a histologic diagnosis of cancer. Participants were interviewed to collect information on the biological relatedness of their parents. Risk of cancer was determined in relation to the presence of parental consanguinity, coefficient of inbreeding (F), and whether subjects were more (F ≥ 0.0625) or less (F < 0.0625) inbred, and was stratified by sex, age group, and cancer type. Results: Reduction of overall cancer risk was associated with increased F (P < 0.001). In men, F was significantly higher in healthy controls than cancer patients overall (P = 0.001) and in both younger (≤30 years) and older age groups (P = 0.003 and 0.013, respectively). In women, reduction of overall cancer risk by increased F was found only in the older age group (P = 0.03). Overall, being more inbred was associated with a reduction in overall cancer risk by about 25% (odds ratio (OR), 0.74; 95% confidence interval (CI), 0.64–0.86). For seven of the eight most common cancer types, the risk of cancer was reduced with increased F but these did not reach conventional statistical significance (P > 0.05). Conclusions: Inbreeding was associated with reduced overall risk of cancer in studied population. Reduction of cancer risk is greater in men than women and, in women, is restricted to those older than 30 years.