Unfavorable cancer mortality-to-incidence ratios in patients with schizophrenia: A nationwide cohort study in Taiwan, 2000–2019

Objectives: Studies on cancer incidence and mortality in patients with schizophrenia have reported inconsistent findings. In this study, we simultaneously investigated cancer incidence and mortality in patients with schizophrenia and evaluated the cancer mortality-to-incidence ratio (MIR), which is rare in the literature. Methods: From the Taiwan National Health Insurance Database, we collected the data of 107,489 patients who received a diagnosis of schizophrenia between 2000 and 2019. Data regarding cancer incidence and mortality were obtained from the Taiwan Cancer Registry and National Mortality Database, respectively. In total, 3881 incident cancer cases and 2288 cancer mortality cases were identified. Standardized incidence ratios (SIRs), mortality rate ratios (MRRs), and MIRs were compared between patients with schizophrenia and the general population. Results: The overall rate of cancer incidence was slightly lower (SIR: 0.95; 95% confidence interval [CI]: 0.92–0.98; p < 0.001) and that of cancer mortality was higher (MRR: 1.29; 95% CI: 1.23–1.3; p < 0.001) in patients with schizophrenia than in the general population. The MIR for overall cancer was significantly higher in the patients with schizophrenia. The relative MIR (MIR of patients with schizophrenia divided by that of the general population) was 1.36 (95% CI: 1.30–1.42). Conclusion: The MIR was significantly higher in the patients with schizophrenia than in the general population, indicating the possible presence of healthcare disparities. Additional studies are required to investigate the potential association between the significantly higher MIR in patients with schizophrenia and healthcare disparities.