COlonic Salvage by Therapeutic Appendectomy.

Rationale: The annual incidence of ulcerative colitis (UC) amounts to 6-8 new cases per 100.000. Patients are initially treated medically, and colitis refractory to medical management is treated surgically, mostly by means of an (emergency) colectomy or a procto-colectomy with ileal J-pouch anastomosis. Over the past 10 years evidence has been accumulating indicating that the appendix has an immunomodulatory role in patients with UC reducing the need for medication and perhaps even colectomy. Objective: The objective of this prospective observational cohort study is to evaluate the effect of appendectomy on the disease course of patients with active ulcerative colitis despite standard step-up treatment including biologicals compared to usual care. The second objective is to evaluate if it is possible to predict response to appendectomy based on preoperative radiological or endoscopic findings by comparing results to histological characteristics in the resection specimen. Study design: The design of the study is a multicentre prospective cohort study including patients with active UC despite standard step-up treatment including optimized biological treatment. Patients failing standard step-up medical treatment (including biologicals), that are discussed in the multidisciplinary meeting to be counselled for a JAK-inhibitor (e.g. tofacitinib, filgotinib) or restorative proctcolectomy with ileal-j pouch anastomosis, will be counselled for appendectomy as an alternative treatment option. All patients will undergo colonoscopy before the start of a new treatment according to current guidelines. Biopsies will be taken to histologically confirm ongoing inflammation. Cecal biopsies will be used to correlate histological findings to response to appendectomy. Patients will undergo assessment of the appendix by ultrasound before surgery. All patients will be followed according to study protocol. Study population: All patients of 16 years and older, with established diagnosis