OP22 The risk of cancer in pediatric-onset immune-mediated inflammatory diseases – a nationwide Danish study from 1980-2018

Abstract Background A higher risk of cancer has been reported among patients with adult-onset immune-mediated inflammatory disease (IMID). However, data on cancer risk in paediatric-onset IMIDs (pIMID) are scarce. In this nationwide study from 1980 to 2018, we investigated the risk of cancer in the Danish pIMID population compared to controls from the background population. Methods PIMID was defined as patients registered in the Danish National Patient Registries with one or more of the following diagnoses: inflammatory bowel disease (pIBD), rheumatic disease (pRD), or autoimmune idiopathic liver disease (pAILD) before their 18th birthday. Each case was matched with up to 10 controls from the background population. Cancer diagnoses were verified using the Danish Cancer Registry. Risk of cancer was calculated using Cox proportional regression analysis and presented as hazard ratios (HR) with 95% confidence intervals (95% CI). Results We identified 13 216 cases, consisting of 5 811 pIBD (44%), 7 241 pRD (55%) and 347 pAILD (2%), and 114 502 controls. Median age at diagnosis was 12.5 years. Follow-up time was 11.1 and 10.5 years for cases and controls, respectively. The risk of overall cancer in pIMID compared to the background population was HR 2.1 (95%CI: 1.8-2.4), p<0.001. The risk of cancer was HR 2.4 (95%CI: 2.0-3.0), p<0.001 in pIBD, ascribed to colorectal-, liver-, skin cancer and lymphoma, HR 1.6 (95%CI: 1.2-2.1), p=0.002 in pRD, ascribed to lymphoproliferative cancer, and HR 5.7 (95%CI: 2.5-13.1), p<0.001 in pAILD, ascribed to liver and skin cancer. Patients with multiple IMID had an increased risk of cancer compared to patients with only one pIMID diagnosis (HR 2.8 [95%CI: 1.9-4.1], p<0.001). Conclusion PIMID was associated with a twofold increased risk of cancer, ascribed to colorectal cancer in pIBD, liver cancer and skin cancer in pIBD and pAILD, and lymphoproliferative cancer in pIBD and pRD.