Cancer in schizophrenia: is the risk higher or lower?

Studies exploring the relationship between schizophrenia and cancer have shown conflicting results. Our study explores this association in three Jewish-Israeli population groups defined by their continent/place of birth (Israel, Europe-America, and Africa-Asia). The identification of the patients was made through the linkage of the nationwide psychiatric and cancer registries. The incidence of cancer in patients diagnosed with schizophrenia was compared with the incidence in the general population. The results showed that the cancer standardized incidence ratios (SIRs) for all sites were significantly lower among men and women with schizophrenia, 0.86 [95% confidence interval (CI) 0.80-0.93] and 0.91 (95% CI 0.85-0.97), respectively. This reduced overall risk was clearest for those born in Europe-America, both men (SIR 0.85, 95% CI 0.74-0.97) and women (SIR 0.86, 95% CI 0.77-0.94). Among women diagnosed with schizophrenia, the SIR was statistically higher for cancer in the breast among those born in Asia-Africa (1.37, 95% CI 1.12-1.63) and in the corpus uteri among the Israel-born (2.75, 95% CI 1.69-3.81) than among their counterparts in the general population. Lung cancer was significantly higher in men born in Asia-Africa diagnosed with schizophrenia than in the respective comparison population group (1.58, 95% CI 1.13-2.2). Our findings, and those of the literature, justify conducting a multinational study that includes identification of cancer-related risk factors among patients with schizophrenia and their families, and information on the use of psychotropic medications. This effort may clarify an epidemiological puzzle that remains outstanding.