Increased incidence of cancer in systemic lupus erythematosus: a Finnish cohort study with more than 25 years of follow-up

Objective: The aim of this study was to assess the cancer risk in a cohort of Finnish patients with systemic lupus erythematosus (SLE) when followed over the long term. Method: The cohort consisted of 182 female and 23 male SLE patients treated at the Helsinki University Central Hospital from 1967 to 1987. The cohort was linked to the Finnish Cancer Registry and followed for cancer incidence from 1967 to 2013. Standardized incidence ratios (SIRs) were calculated by dividing the number of observed cases by the number of expected cases for different types of cancer. Results: The mean duration of follow-up was 25.7 years. Forty-five patients out of 205 were diagnosed with cancer, with an increased risk of overall malignancy [SIR 1.90, 95% confidence interval (CI) 1.39-2.54, p < 0.001]. The incidences of soft-tissue sarcoma (SIR 12.1, 95% CI 1.47-43.7, p < 0.05), non-Hodgkin's lymphoma (SIR 12.1, 95% CI 5.82-22.3, p < 0.001), and kidney cancer (SIR 7.79, 95% CI 2.53-18.2, p < 0.01) were significantly elevated. Conclusion: This long-term study confirms that patients with SLE have an increased risk of cancer, particularly non-Hodgkin's lymphoma and kidney cancer.