EP210 - Synchronous Rectal Adenocarcinoma and Metastatic Ileal Neuroendocrine Tumor: A Case Report of Dual Gastrointestinal Malignancies

Purpose/Background: Synchronous gastrointestinal malignancies are rare and present significant diagnostic and therapeutic challenges, particularly when histologically distinct tumors coexist. Early-stage rectal adenocarcinoma is common and typically managed with curative-intent resection, whereas small bowel neuroendocrine tumors (NETs) are less common and often metastatic at diagnosis, making surgical cure less achievable and often requiring systemic therapy. The coexistence of rectal adenocarcinoma and metastatic ileal NET is uncommon, with limited literature to guide optimal management of dual malignancies with potentially competing therapeutic goals. We present a case illustrating the multidisciplinary surgical management of localized rectal cancer concurrent with metastatic small bowel NET.

Methods/Interventions: A 53-year-old man was referred after a positive fecal immunochemical test. Colonoscopy revealed a fungating rectal mass 15 cm from the anal verge; endoscopic ultrasound confirmed a T2N0 lesion. Cross-sectional imaging demonstrated mesenteric adenopathy, ileal thickening, and a 17 × 15 mm hepatic lesion. DOTATATE PET revealed high somatostatin receptor avidity consistent with metastatic NET involving the liver and periaortic nodes. Following multidisciplinary tumor board, the patient underwent open low anterior resection, small bowel resection with mesenteric lymphadenectomy, hepatic microwave ablation, and cholecystectomy.

Results/Outcomes: Intraoperative assessment identified multiple bilobar hypodense liver lesions with a miliary distribution, confirmed on frozen section as metastatic NET. Complete hepatic clearance was not feasible; cytoreductive ablation of dominant hepatic lesions and resection of the ileal primary with bulky mesenteric nodes were performed. The rectal adenocarcinoma was completely resected with negative margins and a side-to-end colorectal anastomosis performed. Postoperative recovery was uneventful, and the patient was discharged on postoperative day seven. Final pathology demonstrated pT2N0 moderately differentiated rectal adenocarcinoma and well-differentiated NET of the ileum with two hepatic metastases. The patient was initiated on lanreotide therapy and remains radiographically stable at 6 months.

Conclusion/Discussion: Synchronous rectal adenocarcinoma and metastatic small bowel NET represent a rare clinical scenario requiring individualized management. This case highlights the importance of comprehensive staging, intraoperative reassessment, and multidisciplinary coordination to balance curative-intent resection of early rectal cancer with cytoreductive strategies for disseminated NET. In more advanced rectal disease, the need for neoadjuvant chemoradiation could delay or preclude timely NET-directed therapy, underscoring the necessity of sequencing decisions guided by disease biology and patient prognosis. Recognition of such dual malignancies allows for tailored operative planning and systemic management to optimize oncologic and functional outcomes.