S3742 Unexpected Turn: Ileal B-Cell Lymphoma After Treated Colorectal Adenocarcinoma

Introduction: Ileal B-cell lymphoma occurring after colorectal adenocarcinoma is an uncommon clinical scenario, presenting a diagnostic and therapeutic challenge. While colorectal cancer is the third most commonly diagnosed cancer worldwide, primary gastrointestinal lymphoma makes up only 1%-4% of all GI malignancies. Lymphomas as secondary primary malignancies are infrequently reported post-colorectal cancer. Herein we present a case of an 83-year-old woman who presented with small bowel obstruction after treated colorectal adenocarcinoma and found to have a secondary primary B-cell lymphoma. The case highlights diagnostic complexity and importance of vigilant follow-up in patients with prior malignancies. Case Description/Methods: Patient is an 83-year-old woman with a history of colorectal cancer status post resection and chemotherapy in remission for approximately 15 years presenting with nausea and vomiting. Patient was found to have a partial bowel obstruction that did not resolve with conservative management. Abdominal computerized tomography (CT abdomen) revealed a 6.4 × 3.1 cm soft tissue mass causing significant ileal luminal narrowing and extending into the cecum. Colonoscopy was performed with findings of incomplete severe luminal narrowing at the level of the terminal ileum. Biopsies revealed diffuse large B cell lymphoma. Several multi-disciplinary conversations were held with family. Patient ultimately decided to proceed with chemotherapeutic treatment. The first round of therapy was performed at the hospital and patient was discharged home once stable. Follow-up CT abdomen revealed no mechanical obstruction. Follow-up conversation with the patient's daughter several weeks later revealed the patient was nearly back to baseline, tolerating a regular diet and plans to continue outpatient chemotherapy. Discussion: This case highlights the rare occurrence of ileal B-cell lymphoma following colorectal adenocarcinoma in an elderly patient, presenting as small bowel obstruction. Primary small bowel lymphomas are uncommon and often pose diagnostic challenges due to nonspecific symptoms. The temporal relationship suggests the need for vigilance in patients with a history of malignancy, as immune changes and prior cancer therapies may predispose to secondary neoplasms. Early imaging and histological evaluation are essential for accurate diagnosis. This case highlights the importance of considering alternative diagnoses in elderly patients with new gastrointestinal symptoms post-cancer treatment.