Malignancy rates in children, young people and adults with JIA: an observational study using CPRD Aurum

JIA affects ∼1-2/2000 children in the UK. Adults with inflammatory arthritis have ∼10% increased malignancy risk. JIA malignancy rates in Nordic data are 3-5/10 000 person years, with conflicting evidence on comparative risk. This study calculated malignancy rates in England of patients with JIA, vs matched controls and general population estimates.

Using UK Primary Care data (CPRD) Aurum, this retrospective cohort study matched patients with JIA (diagnosed <16 years) 4-to-1 with non-JIA controls in England by birth year, gender and practice. Malignancies were identified from (i) NHS-linked hospitalization data and (ii) CPRD read codes. Exposure started at first JIA code date (or matched date for controls), 1 January 2000, or CPRD entry date, whichever was latest. Follow-up continued until end of follow-up of JIA-matched patient (for controls), end of CPRD follow-up, 31 December 2018, first malignancy or death, whichever was first. Cox-proportional hazards models compared malignancy rates. Standardized incidence ratios (SIRs) were calculated against ONS general population estimates by calendar year, age and gender.

A total of 3714 patients with JIA and 10 858 matched controls were identified; demographics were similar. Malignancy rates were 6.8 per 10 000 (95% CI: 4.4-10.7) in JIA and 3.1 per 10 000 person years (95% CI: 2.0-4.6) in controls; HR 2.2 (95% CI: 1.2-4.1). Both cohorts had raised SIRs compared with ONS general population estimates.

This study found that those with JIA had a doubling risk for malignancies compared with the matched control population. However, it is important to note that malignancy in this JIA patient population is extremely rare with the absolute risk remaining very low.