Association between schizophrenia and prostate cancer risk: Results from a pool of cohort studies and Mendelian randomization analysis

Background: Observational studies analyzing the risk of prostate cancer in schizophrenia patients have generated mixed results. We performed a meta-analysis and a Mendelian randomization (MR) analysis to evaluate the relationship and causality between schizophrenia and the risk of prostate cancer. Methods: A comprehensive and systematic search of cohort studies was conducted, and a random-effects model meta-analysis was performed to calculate the standardized incidence ratios (SIRs) for prostate cancer incidence among schizophrenia patients versus the general population. To investigate the correlation between genetically-predicted schizophrenia and prostate cancer risk, we used summary statistics from the Prostate Cancer Association Group to Investigate Cancer Associated Alterations in the Genome (PRACTICAL) consortium (61,106 controls and 79,148 cases), and 75 schizophrenia-associated single nucleotide polymorphisms (SNP) from European descent as the instrumental variable. Results: In the meta-analysis of 13 cohort studies with 218,076 men involved, a decreased risk of prostate cancer was observed among schizophrenia patients [SIR 0.610; 95% confidence interval (CI) 0.500-0.740; p < 0.001] with significant heterogeneity (I-2 = 83.3%; p < 0.001). However, MR analysis did not sustain the link between genetically-predicted schizophrenia and prostate cancer [odds ratio (OR) 1.033; 95% CI 0.998-1.069; p = 0.065]. The result was robust against extensive sensitivity analyses. Conclusions: Our study indicated a decreased risk of prostate cancer in schizophrenia patients through meta-analysis, while MR analysis did not support the connection between schizophrenia and prostate cancer. Due to the interaction of genetic variants between binary exposures, we need to be cautious in interpreting and presenting causal associations. Moreover, further research is needed to investigate underlying factors that might link schizophrenia to the risk of prostate cancer.