Background
Microscopic colitis (MC) is a chronic inflammatory condition of the colon, resulting in an impaired quality of life due to debilitating watery diarrhea. First-line therapy consists of budesonide, though a subset of patients is refractory or becomes budesonide- dependent. Evidence for the efficacy of biologicals or small molecules in MC is sparse and limited to small case series. Hence, we aimed to generate more real-life efficacy data.

Methods
This retrospective series was collected as part of the CONFER project by ECCO and supported by the European Microscopic Colitis Group (EMCG). Cases of MC patients treated with advanced therapies were included through a standardised collection form. Clinical response was defined as a 50% reduction in stool frequency (SF); clinical remission was defined according to the Hjortswang criteria as < 3 stools/day or < 1 watery stool/day.

Results
Ninety-nine patients were identified (Table 1), of whom all but one were previously treated with budesonide. Reasons for budesonide discontinuation included primary non-response (PNR, 16.3%), refractory disease (34.7%), budesonide dependency (38.8%), or adverse events (AE, 10.2%). In total, 165 treatment cycles with advanced therapy (47 IFX, 40 ADA, 47 VDZ, 10 UST, 14 JAK inhibitors, 7 other) were reported. First-line advanced therapies included mainly anti-TNF (76.8%) and VDZ (20.2%) (Figure 1A). Patients were exposed to anti-TNF therapy for a median of 1.4 [0.5-3.1] years, with a significant drop in SF after induction (p<0.001), resulting in 50.0% clinical remission (Figure 1B). However, 63.0% ultimately discontinued anti-TNF therapy, mainly due to PNR (37.9%), loss-of-response (LOR, 36.2%) or AE (20.7%). VDZ induced 46.8% clinical remission, reflected in a significant drop in SF (p<0.001). Though, a 59.6% discontinuation rate was observed after a median 0.6 [0.3-1.3] years, mainly due to PNR (63.0%) and LOR (22.2%). Similarly, for UST a 40.0% clinical remission rate was accompanied by 60.0% therapy withdrawal, primarily due to PNR (83.3%). In contrast, JAK inhibition resulted in 78.6% clinical remission, with a substantial drop in SF (p=0.002) and 21.4% discontinuation rate after a median exposure of 0.6 [0.3-1.6] years.

Conclusion
Almost all advanced therapies are used in budesonide refractory or dependent MC, with anti-TNF agents the most often used first-line options. However, anti-TNF discontinuation is frequent due to lack/loss of efficacy. VDZ and UST could be alternatives, but also have a substantial discontinuation rate. In this retrospective series, the small number (n=14) of JAK inhibitor treated patients had the highest remission rate, suggesting further research on the role of JAK inhibitors in MC.

<b>Figure 1</b><br /> <br /> Figure 1A: Advanced therapies used to treat MC patients, with a split by 1<sup>st</sup>, 2<sup>nd</sup>, 3<sup>rd</sup> or 4<sup>th</sup> line per mechanism of action.<br /> <br /> <br /> Figure 1B: Clinical response and remission rates after induction per mechanism of action. <div id=

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Figure 1

Figure 1A: Advanced therapies used to treat MC patients, with a split by 1^st, 2^nd, 3^rd or 4^th line per mechanism of action.

Figure 1B: Clinical response and remission rates after induction per mechanism of action.

<b>Table 1: </b>Baseline characteristics of all included patients <div id=

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Table 1: Baseline characteristics of all included patients

Signe Wildt

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