S5063 Diarrheal Dilemma: A Case of Post-CAR-T T-Cell Lymphoma Presenting as Refractory Diarrhea

Introduction: Chimeric antigen receptor T-cell (CAR-T) Therapy is an increasingly popular treatment for managing refractory leukemia and lymphoma. Recently, the FDA announced an investigation into CAR-T regimens due to an increase in reports of secondary cancers. One rarely cited secondary cancer is T-cell lymphoma after ciltacabtagene autoleucel (Cilta-cel) in patients with multiple myeloma (MM). We present a case of refractory diarrhea secondary to small bowel T-cell lymphoma. Case Description/Methods: A 75-year-old man with a history of multiple myeloma presented to the emergency department with recurrent profuse watery diarrhea 4 months after completing Cilta-cel therapy. During a recent hospitalization for the same issue, infectious workups and colonoscopy yielded no positive findings. A computed tomography (CT) scan revealed intra- and extrahepatic biliary duct dilation, and magnetic resonance cholangiopancreatography (MRCP) indicated common bile duct (CBD) dilation of 1.1 cm with distal narrowing. Additional laboratory tests showed a stool osmotic gap indicative of osmotic diarrhea and an elevated gastrin level. A celiac panel, fecal calprotectin, fecal fat, fecal elastase, serotonin level, VIP level, and 5-HIAA level were all within normal limits. Esophagogastroduodenoscopy combined with endoscopic ultrasound revealed loss of gastric rugae, no intraluminal or pancreatic masses, and infiltration of cytotoxic CD4+ T-cells in the superficial intestinal mucosa. A repeat endoscopy with biopsies demonstrated diffuse cytotoxic T-cell infiltration. In collaboration with Pathology and Oncology, the patient was diagnosed with post-CAR-T T-cell lymphoproliferative disorder of the small bowel. Following interdisciplinary collaboration, infliximab was initiated due to concerns regarding autoimmune etiology; however, the diarrhea worsened. He was switched to high-dose steroids, resulting in improvement, and he was discharged in stable condition on a steroid taper with close follow-up. Discussion: CAR-T is an increasingly popular treatment for managing refractory leukemia and lymphoma; however, it also has complications. Our patient experienced an exceptionally rare adverse effect several months after treatment for his MM, which is not well documented in the literature. He was eventually diagnosed with refractory diarrhea caused by the development of CD4-positive T-cell lymphoma in the small bowel following treatment with ciltacabragene autoleucel. It is essential to recognize that rare complications can occur with CAR-T therapy.