EP395 - Synchronous Mantle Cell Lymphoma and Sigmoid Colon Adenocarcinoma: A Rare Collision Tumor with Dual Pathogenesis

Purpose/Background: Collision tumors involving colorectal adenocarcinoma and hematolymphoid malignancies are exceptionally rare, representing less than 0.3% of all colorectal neoplasms. Among them, mantle cell lymphoma (MCL) is an uncommon B-cell subtype that may present as multiple lymphomatous polyposis throughout the gastrointestinal tract. We present a rare case of synchronous MCL and sigmoid adenocarcinoma occurring in the same anatomical region, highlighting diagnostic and therapeutic challenges.

Methods/Interventions: A 73-year-old man with a history of hypertension and known mantle cell lymphoma under oncologic follow-up was referred for evaluation of a sigmoid mass detected on colonoscopy. Endoscopic examination revealed diffuse nodular mucosa throughout the colon, a 0.8 cm sessile polyp in the transverse colon, and a 4 cm ulcerated mass in the sigmoid colon involving one-third of the circumference.

Histopathology demonstrated two distinct neoplasms: (1) a moderately differentiated intestinal-type adenocarcinoma and (2) a mantle cell lymphoma of classic morphology, characterized by small-to-medium lymphocytes positive for CD20, PAX5, BCL2, Cyclin D1, SOX11, and p53, with a proliferation index (Ki-67) of 15%, and negative for CD3, CD5, CD10, CD23, BCL6, MUM1.

Preoperative imaging (CT, PET-CT, MRI) showed sigmoid wall thickening and small presacral and mesorectal lymph nodes (≤5 mm) without distant metastases. .

Results/Outcomes: The patient underwent sigmoidectomy with Hartmann's colostomy, achieving R0 resection. Twelve lymph nodes were negative for metastatic carcinoma. Postoperative management included multidisciplinary discussion for sequential systemic therapy targeting residual MCL

Conclusion/Discussion: DISCUSION

Only a handful of cases of synchronous colorectal adenocarcinoma and MCL have been reported worldwide. The coexistence likely represents two independent neoplastic processes rather than clonal transformation. This dual pathology emphasizes the importance of complete colonoscopic evaluation and extensive immunohistochemistry in patients with hematologic malignancies presenting with gastrointestinal lesions. Surgical resection remains the cornerstone for localized adenocarcinoma, while systemic immunochemotherapy is required for MCL.

CONCLUSION

This case underscores the diagnostic complexity of colorectal collision tumors and the necessity of multidisciplinary coordination. Early recognition of synchronous hematolymphoid and epithelial malignancies allows curative-intent treatment and tailored postoperative management.

COLONOSCOPY