Cancer risk among parents and siblings of patients with schizophrenia

Background: A reduced risk of cancer has been noted among people with schizophrenia. Given that genetic causes have been proposed as an explanation of this finding, one would expect that the risk of cancer among first-degree relatives would be equally reduced. Aims: To investigate the risk of cancer among the biological parents and full siblings of people receiving in-patient care for schizophrenia. Method: Linkage analysis was conducted between national population, psychiatric and cancer databases. Standardised incidence ratios for all cancer sites were calculated by comparing the incident rates among first-degree relatives with national incidence rates. Results: A reduced cancer risk was found across all groups examined. Among parents, whose numbers were adequately large, the findings reached statistical significance. For index cases and siblings - a markedly younger population - only a trend was elicited. Conclusions The genetic hypothesis - namely, the presence of a gene with the dual effect of reducing the cancer risk and disrupting neurodevelopment - is a plausible explanation for these findings.