Malignancy Rates in children, young people, and adults with Juvenile Inflammatory Arthritis (JIA): an observational study using CPRD Aurum.

Abstract

Juvenile Inflammatory Arthritis (JIA) affects ∼1-2/2,000 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, practice. Malignancies were identified from (i) NHS-linked hospitalisation data, and (ii) CPRD read codes. Exposure started at first JIA code date (or matched-date for controls), 1-Jan-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-Dec-2018, first malignancy, or death, whichever was first. Cox-proportional hazards models compared malignancy rates. Standardised incidence ratios (SIRs) were calculated against ONS general population estimates by calendar year, age, gender. 3,714 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.