| Summary: | Abstract Background Previous studies have shown conflicting evidence regarding the incidence of cancer in patients with systemic lupus erythematosus (SLE) compared with that in healthy individuals. Calcineurin inhibitors (CNIs) such as cyclosporine and tacrolimus have been widely used to treat SLE; however, their effects on cancer risk remain unclear. We aimed to investigate the incidence of cancer in patients with SLE and determine the potential association between CNI use and cancer risk. Methods The standardized incidence ratio (SIR) of cancer among patients with lupus in the Lupus Registry of Nationwide Institutions (LUNA) was calculated based on the age-standardized incidence rate of cancer reported by Japan’s Ministry of Health, Labour and Welfare. We also examined the association between CNI exposure and cancer risk, while considering potential confounding factors. The analysis accounted for confounding variables such as age, sex, smoking history, maximum glucocorticoid dose, treatment history with cyclophosphamide, ongoing hydroxychloroquine, Systemic Lupus International Collaboration Clinics/American College of Rheumatology Damage Index (SDI) value (excluding cancer occurrence), comorbidity of diabetes mellitus, and smoking history. Results The study included 704 patients with SLE (625 females; 88.8%) with a median age of 44 years [interquartile range (IQR) = 34–55] years. The median past maximum glucocorticoid dose was 40 mg/day [IQR = 30–60 mg/day], and the SDI at registration was 1 [IQR = 0–2]. Among the patients, 246 (35.1%) had smoking histories, and 38 (5.4%) experienced cancer complications. Gynecological malignancies accounted for 63.2% of all cancers. The SIR of cancer in the LUNA cohort was 1.08 (95% confidence interval [CI] = 0.74–1.43). No statistically significant risks of cancer were found in relation to CNI treatment history; the odds ratio using multiple logistic regression was 1.12 (95% CI = 0.42–3.00), the risk ratio using standardization was 1.18 (95% CI = 0.47–2.16), and the risk ratio using inverse probability weighting was 1.8 (95% CI = 0.41–4.66). Conclusions The incidence of cancer in patients with SLE in the LUNA cohort did not significantly differ from that in the general population. These findings suggest that CNI treatment in this cohort did not pose a risk factor for cancer development.
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