Obinutuzumab-Induced Inflammatory Bowel Disease-Like Colitis.

Introduction: Obinutuzumab, an anti-CD20 antibody, is widely used in the treatment of B-cell lymphomas. While diarrhea is a known side effect, obinutuzumab-induced inflammatory bowel disease (IBD)-like conditions are rarely reported. Here, we present a case of obinutuzumab-induced pancolitis. Case Presentation: A 69-year-old male with stage IV follicular lymphoma, treated with obinutuzumab-CHOP and subsequent obinutuzumab maintenance therapy, developed non-bloody diarrhea after his third maintenance dose. Endoscopic and histological findings mimicked Crohn's disease, leading to a diagnosis of obinutuzumab-induced pancolitis. Obinutuzumab was discontinued, and the patient was transitioned to infliximab therapy, leading to partial improvement. Conclusion: This case demonstrates a severe instance of obinutuzumab-induced pancolitis with IBD-like features, emphasizing the need for clinicians to consider drug-induced etiologies in patients presenting with new gastrointestinal symptoms during obinutuzumab therapy. Timely diagnosis and a multidisciplinary approach are crucial for effective management. Further reports are needed to better understand the full spectrum of gastrointestinal toxicity associated with obinutuzumab and guide future treatment.