For nearly a century, the incidence of cancer in people with schizophrenia was lower than in the general population. In the recent decade, the relationship between cancer and schizophrenia has become obscured. Thus, we investigated the cancer risk among young and middle-aged patients with schizophrenia.

Records of newly admitted patients with schizophrenia (n = 32 731) from January 2000 through December 2008 were retrieved from the Psychiatric Inpatient Medical Claims database in Taiwan, and the first psychiatric admission of each patient during the same period was defined as the baseline. We obtained 514 incident cancer cases that were monitored until December 2010. Standardised incidence ratios (SIRs) were calculated to compare the risk of cancer between those with schizophrenia and the general population. Stratified analyses of cancer incidences were performed by gender, site of cancers and duration since baseline (first psychiatric admission).

The incidence of cancer for all sites was slightly higher than that of the general population for the period (SIR = 1.15 [95% CI 1.06–1.26], p = 0.001). Men had a significantly higher incidence of colorectal cancer (SIR = 1.48 [95% CI 1.06–2.06], p = 0.019). Women had a higher incidence of breast cancer (SIR = 1.47 [95% CI 1.22–1.78], p < 0.001). Intriguingly, the risk for colorectal cancer was more pronounced 5 years after the first psychiatric admission rather than earlier (SIR = 1.94 [1.36–2.75], p < 0.001) and so was the risk for breast cancer (SIR = 1.85 [1.38–2.48], p < 0.001). The cancer incidence was higher in patients with schizophrenia contradicting the belief that schizophrenia was protective of cancers.

Our analyses suggest that men and women with schizophrenia were more vulnerable to certain types of cancers, which indicates the need for gender-specific cancer screening programs. The fact that risk of colorectal cancer was more pronounced 5 years after the first psychiatric admission could imply the impact of unhealthy lifestyles or the possibility of delayed diagnoses.