Pathological assessment of gastrointestinal biopsies from patients with idelalisib-associated diarrhea and colitis.

Aim: Idelalisib (IDELA) treatment is associated with diarrhea/colitis (incidence of approximate to 15% grade3). We performed a retrospective analysis of gastrointestinal biopsies from 29 patients treated with IDELA across nine clinical trials. Methods: A central core laboratory performed histopathologic review, immunohistochemistry, and droplet digital PCR viral studies. These results were correlated with tissue immune profiling data and morphologic features per modified Geboes score. Results: Out of 29 eligible patients with abdominal pain or diarrhea, 24 (82.8%) had reported adverse event terms of diarrhea and/or colitis. Infectious pathogens were detected in 9/29 samples. Most biopsies presented with mixed/inflammatory infiltrates and contained increased numbers of FOXP3(+) cells versus normal controls. Conclusion: This study revealed evidence of T-cell dysregulation and a substantial infectious component in association with IDELA-related diarrhea/colitis.