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It is unclear if the association between rheumatoid arthritis (RA) and a higher risk of prostate cancer (Pca) reflects a causal relationship. We conducted a meta-analysis and used the Mendelian randomization method (MR) to evaluate the association between RA and Pca risk. A meta-analysis and subgroup analysis of the incidence of Pca in patients with RA was conducted. To determine whether genetically elevated RA levels were causally linked to Pca, two MR samples were employed. To eliminate gender-related bias, we conducted a stratified analysis of the GWAS data for RA by gender, specifically including 140,254 males. Additional MR analysis was also performed to determine potential confounding factors influencing the association between genetically susceptible RA and Pca. In total, 409,950 participants were enrolled in 20 trials to investigate the Pca risk in patients with RA. The meta-analysis suggested that RA was unrelated to the Pca risk (SIR = 1.072, 95% CI, 0.883–1.261). However, a subgroup analysis showed that low smoking rates might increase the Pca risk in patients with RA by 24%. The MR analysis showed that increased genetic susceptibility to RA was related to a high Pca risk (OR = 36.20, 95%CI = 1.24–1053.12, P = 0.037). The causality estimation of MR-Egger, Weighted mode, Simple mode, and Weighted median method were similar in direction and magnitude. Although our meta-analysis found no correlation between RA and Pca risk, MR analyses supported a causal relationship between genetic susceptibility to RA and increased prostate risk. Early attention to Pca risk in patients with RA may be important for improving prognosis and mortality in such patients. Further research is needed to determine the etiology of RA attributed to Pca and its underlying mechanisms. [ABSTRACT FROM AUTHOR]

Background: Current observational studies suggest that there may be a causal relationship between systemic lupus erythematosus (SLE) and prostate cancer (PC). However, there is contradictory evidence. This study aimed to investigate and clarify the association between SLE and PC. Methods: We searched PubMed, Embase, Web of Science, and Scopus until May 2022. A meta-analysis was conducted on the standard incidence rate (SIR) and 95% CI. Subgroup analysis was performed based on the follow-up duration, study quality, and appropriate SLE diagnosis. Mendelian randomization (MR) of the two samples was used to determine whether genetically elevated SLE was causal for PC. Summary MR data were obtained from published GWASs, which included 1,959,032 individuals. The results were subjected to sensitivity analysis to verify their reliability. Results: In a meta-analysis of 79,316 participants from 14 trials, we discovered that patients with SLE had decreased PC risk (SIR, 0.78; 95% CI, 0.70–0.87) significantly. The MR results showed that a one-SD increase in genetic susceptibility to SLE significantly reduced PC risk (OR, 0.9829; 95% CI, 0.9715–0.9943; P = 0.003). Additional MR analyses suggested that the use of immunosuppressants (ISs) (OR, 1.1073; 95% CI, 1.0538–1.1634; P < 0.001), but not glucocorticoids (GCs) or non-steroidal anti-inflammatory drugs (NSAIDs), which were associated with increased PC risk. The results of the sensitivity analyses were stable, and there was no evidence of directional pleiotropy. Conclusions: Our results suggest that patients with SLE have a lower risk of developing PC. Additional MR analyses indicated that genetic susceptibility to the use of ISs, but not GCs or NSAIDs, was associated with increased PC risk. This finding enriches our understanding of the potential risk factors for PC in patients with SLE. Further study is required to reach more definitive conclusions regarding these mechanisms. [ABSTRACT FROM AUTHOR]