Hashash, Jana G.

ABSTRACT Background Inflammatory bowel disease (IBD) and myeloproliferative neoplasms (MPNs) share chronic inflammation and immune dysregulation. Aim We evaluated the incidence of MPNs among patients with IBD and clinical outcomes of IBD–MPN coexistence. Methods Two retrospective cohort analyses were conducted using the TriNetX database. First, adults with ulcerative colitis (UC) or Crohn's disease (CD) were compared with matched non‐IBD controls to estimate incident MPN risk. A coexistence second analysis included patients with UC or CD who developed MPNs and then were matched to IBD without MPN controls to assess 5‐year outcomes, including IBD‐related complications, surgical interventions, colorectal cancer (CRC) and primary sclerosing cholangitis (PSC). Medication subgroup analyses were performed to evaluate associations with MPN risk. Results After matching, 3873 patients with UC–MPN and 3474 patients with CD–MPN were included. Compared with matched non‐IBD controls, incident MPN risk was higher in UC (HR 1.60, p = 0.01) and CD (HR 1.56, p < 0.001). In CD, MPN coexistence was associated with higher risks of CRC (HR 1.52, p = 0.012), intestinal fistula (HR 2.84, p < 0.001), obstruction (HR 2.05, p < 0.001), perforation (HR 2.37, p < 0.001), small bowel resection (HR 3.69, p < 0.001) and colectomy (HR 2.10, p < 0.001). In UC, MPN coexistence was associated with higher risks of CRC (HR 1.50, p = 0.001), PSC (HR 1.75, p = 0.03) and pouchitis (HR 1.68, p = 0.003). Exposure to thiopurines (HR 1.28, p < 0.001) was associated with increased MPN risk, whereas TNF, IL‐23 and JAK inhibitors were not. Conclusions IBD is associated with increased MPN risk, and IBD–MPNs coexistence is associated with worse IBD‐related complications and malignancy risk.