EP784 - Case Report On Synchronous Colon Adenocarcinoma With Rectal Carcinoid Tumor With Pelvic Lymph Node Metastasis

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Purpose/Background: Adenocarcinoma is the most common cancer of the colon and rectum, while carcinoids are rare, slow-growing neuroendocrine tumors often found incidentally during rectal exams or endoscopies. The occurrence of a rectal carcinoid alongside colon adenocarcinoma is infrequent, particularly in the Philippines, with no known reports of synchronous cases of carcinoids with iliac lymph node metastasis. The prognosis for patients typically hinges more on the adenocarcinoma than on the carcinoid tumor, although lymph node metastasis in rectal carcinoids can also influence prognosis and management. This article discusses a case of sigmoid adenocarcinoma with an incidental rectal carcinoid exhibiting lateral lymph node metastasis.

Methods/Interventions: We report a case involving a 68-year-old man who presented with blood-tinged stools and bloating. Colonoscopy revealed a semi-circumferential mass in the sigmoid colon, occupying 60% of the lumen with areas of ulceration. Metastatic workup ruled out liver and lung metastases. A contrast CT scan showed enlarged right internal iliac lymph nodes, with the largest measuring 17 x 25 mm. A multidisciplinary meeting concluded that surgery should be the first-line treatment despite possible stage 4 disease. The patient underwent exploratory laparotomy, sigmoidectomy, and right lateral pelvic lymph node dissection. A digital rectal exam revealed a rectal polyp, leading to a subsequent transanal excision with full thickness excision.

Results/Outcomes: The patient had an uneventful postoperative recovery and was discharged on the fifth day with good diet tolerance and no surgical site infection. Final histopathology revealed grade 2 moderately differentiated sigmoid adenocarcinoma invading through the muscularis propria, with no lymphovascular or perineural invasion and negative margins. Two out of 20 pericolic lymph nodes tested positive for metastases (pT2N1b). Additionally, the rectal polyp was diagnosed as a well-differentiated grade 1 neuroendocrine tumor, measuring 0.5 cm, with one of five lateral pelvic lymph nodes noted to be metastatic (pT1aN1) with negative basal margins. The patient was classified as having stage IIIA sigmoid adenocarcinoma (pT2N1bM0) and stage IIIB synchronous rectal carcinoid (pT1aN1M0). He was referred to medical oncology for adjuvant chemotherapy with the CAPEOX/FOLFOX regimen, along with standard surveillance per NCCN guidelines.

Conclusion/Discussion: This case illustrates the management of sigmoid adenocarcinoma, initially considered for stage 4 due to identified lymph node metastases. Surgical intervention included sigmoidectomy and lateral pelvic lymph node dissection, along with transanal resection of a rectal polyp. The findings necessitate a multidisciplinary approach to treatment, especially with iliac lymph node involvement in small neuroendocrine tumors, which may complicate prognosis. Localized rectal NETs typically require surgical resection, while tumors larger than 2 cm or with lymph node involvement may necessitate more extensive procedures. Given the rarity of synchronous colon adenocarcinomas and rectal carcinoids, comprehensive diagnostic evaluations are crucial. This case emphasizes the importance of thorough examinations and adequate surgical excisions. Postoperative management should be tailored to the prognosis of both malignancies, with focused surveillance and patient education encouraged for optimal outcomes.