Risk of malignancy in children with juvenile idiopathic arthritis not treated with biologic agents.

Objective: To estimate the relative risk of incident cancer diagnosis among patients with juvenile idiopathic arthritis (JIA) compared to patients without JIA.

Methods: A cohort of biologics-naive patients diagnosed with JIA between 1998 and 2007 and a matched cohort of comparators without JIA were assembled from the PharMetrics Patient-Centric Database. The primary outcome was any incident malignancy, excluding nonmelanoma skin cancer and carcinoma in situ. Claims profiles of patients with any cancer-related diagnosis codes were reviewed to determine outcomes. Incidence rates and 95% confidence intervals (95% CIs) of cancer were calculated and compared between cohorts using Cox proportional hazards regression. Standardized incidence ratios (SIRs) for each cohort compared to the general population were calculated using reference rates from the US Surveillance, Epidemiology, and End-Results (SEER) program.

Results: The JIA and non-JIA cohorts included 3,605 and 37,689 patients, respectively, with a mean age of 11 years. The incidence rates of cancer were 67.0 (95% CI 1.3-132.5) cases/100,000 person-years (PY) for JIA and 23.2 (95% CI 12.2-34.2) cases/100,000 PY for non-JIA. The risk of cancer associated with biologics-naive JIA was elevated (hazard ratio 2.8, 95% CI 0.9-8.3). The JIA cohort had a significantly elevated SIR of 4.0 (95% CI 2.6-6.0); the non-JIA cohort SIR was not significantly above SEER rates (SIR 1.4, 95% CI 0.6-2.6).

Conclusion: We found a nearly 3-fold increased risk of cancer in biologics-naive JIA patients, which approached significance despite the small number of outcomes. This finding suggests an elevated underlying risk of cancer in this disease population.