S3998 A Rare Presentation of Relapsed Mantle Cell Lymphoma Within the Colon

Introduction: Mantle cell lymphoma (MCL) represents a rare subset of non-Hodgkin B-cell lymphoma and typically carries a poor prognosis. MCL most commonly impacts the lymph nodes of males over the age of 60 and spreads to the bone marrow, liver, and, less commonly, to the gastrointestinal (GI) tract. Below we present a unique case of an elderly patient with a known history of MCL previously in remission who developed relapsed disease within the colon nearly twenty years after initial diagnosis. Case Description/Methods: An 83-year-old woman presented to the Emergency Department with acute onset of generalized weakness in the setting of decreased appetite and persistent diarrhea for several weeks after starting pirtobrutinib. The patient was first diagnosed with mediastinal MCL in 2005 and completed 6 cycles of rituximab with fludarabine in 2006. A follow-up positron emission tomography (PET) scan showed no recurrence and screening colonoscopy in 2011 was without abnormalities. MCL subsequently relapsed in the mediastinum in 2021. The patient was started on zunibrutinib with complete response and had a negative PET scan in 2022. Zunibrutinib was continued until the patient developed a community acquired pneumonia prompting transition to pirtobrutinib. Shortly after transition and one week prior to presentation, an out-patient PET Scan showed increased uptake in the distal sigmoid colon, mediastinal lymph nodes, and lungs bilaterally. On arrival, the patient was hemodynamically stable, but hemoglobin was 6.8 gm/dL (down from baseline of 10). After resuscitation, colonoscopy was completed and a polypoid lesion in the sigmoid colon was identified, as well as, a lipomatous ileocecal valve with arteriovenous malformations and friable tissue. Biopsies were taken from each site and hemospray was applied for hemostasis. Pathology was consistent with MCL in both locations. GI bleeding resolved and the patient was discharged home after treatment for concurrent pneumonia. The patient returned several weeks later with profound sepsis secondary to pneumonia and palliative measures were pursued. Discussion: This case describes an unusual presentation of relapsed MCL within the colon and highlights the diagnostic challenges of distinguishing relapsing disease from other potential causes. It reinforces the importance of a broad differential diagnosis along with the timely use of imaging and endoscopy in the workup of GI symptoms in patients with a history of MCL.