Cancer in parents of persons with schizophrenia: Is there a genetic protection?

A reduced risk for cancer has been noted among persons with schizophrenia as well as their first degree relatives. One explanation for these findings suggests that genes associated with schizophrenia confer reduced cancer susceptibility. Given the well documented genetic factor in schizophrenia it could thus be expected that cancer incidence rates should be lower in persons with schizophrenia with a known family history of schizophrenia compared to persons with sporadic schizophrenia, as well as their first degree relatives. This study investigated the risk for cancer among the biological parents of persons with schizophrenia accounting for the familial aggregation. Linkage was conducted between national population, psychiatric and cancer databases. Standardized incidence rates for all cancer sites were calculated by comparing the parents' rates with those of the general population. In addition, the association between familial aggregation of schizophrenia and risk for cancer was calculated among the parents. A reduced cancer risk was found among the parents compared to the general population (SIR 0.8, 95% CI 0.8-0.9). However, no evidence of decreased risk was associated with familial schizophrenia. Thus, no association between familial aggregation and cancer incidents was found with regard to most cancer sites. Moreover, a small, but not statistically significant increased risk of colon cancer was associated with familial aggregation scores among the parents (OR 1.2, 95% CI 1.0-1.5). These findings undermine the support to the genetic explanation for the reduced risk for cancer in schizophrenia among patients and their biological parents.