Association between systemic lupus erythematosus and cancer: findings from cohort studies and Mendelian randomization analysis

Background: Observational studies suggested that systemic lupus erythematosus (SLE) was associated with an increased risk of cancer, however, the causal effect remains unclear. We aim to determine the causality between SLE and cancer using a meta-analysis and Mendelian randomization (MR) approach. Methods A systematic search was conducted using PubMed to identify cohort studies published before January 21, 2021. Meta-analysis was performed to calculate relative risk (RR) and corresponding 95% confidence intervals (CI), and the potentially causal relationships identified by observational studies were further validated using two-sample Mendelian randomization. Results Through meta-analysis of 43 cohort studies involving 231,499 patients, we observed an increased overall cancer risk among SLE patients (RR = 1.62, 95% CI, 1.47–1.79). Site-specific analysis suggested that SLE patients were associated with an increased risk of 17 cancers. Mendelian randomization analysis indicated that genetically predisposed SLE was causally associated with an increased risk of lymphoma (odds ratio = 1.0004, 95% CI, 1.0001–1.0007, P = 0.0035), whereas a decreased risk of bladder cancer (odds ratio = 0.9996, 95% CI, 0.9994–0.9998, P = 0.00004) in European ancestry. However, no relationship was observed between genetically predisposed SLE and risk of colon, pancreatic, lung, cervical and Non-melanoma skin cancer in European ancestry, liver cancer and lung cancer in Asian ancestry. Conclusions Findings from meta-analysis and Mendelian randomization analysis suggested that SLE might be causally associated with an increased risk of lymphoma. However, inconsistent results were observed between SLE and risk of bladder cancer.