# Small Cell Carcinoma of the Rectum Associated With a Tubulovillous Adenoma: An Atypical Case Presentation

## TL;DR

A rare case of rectal small cell carcinoma linked to a tubulovillous adenoma is reported, highlighting diagnostic challenges in patients with multiple cancers.

## Contribution

This case report adds to the limited literature on the rare association between small cell carcinoma of the rectum and tubulovillous adenoma.

## Key findings

- SCCR was diagnosed post-surgery in a patient with concurrent hepatocellular carcinoma.
- The tumor originated from a tubulovillous adenoma, a rare pathological association.
- Standard care protocols were successfully applied despite complex comorbidities.

## Abstract

Small cell carcinoma of the rectum (SCCR) is a rare and aggressive neuroendocrine tumor. Its association with a tubulovillous adenoma is an exceptional occurrence, presenting significant implications for diagnosis and treatment. This case report details a 62-year-old male, undergoing treatment for hepatocellular carcinoma, presented with symptoms of diarrhea. A colonoscopy initially suggested a benign tubulovillous adenoma, but the presence of discordant clinical findings led to further evaluation. The final diagnosis, established post-surgery, was SCCR originating from a tubulovillous adenoma. This case highlights the diagnostic challenges when unusual presentations arise from atypical pathological findings, especially in patients with concurrent malignancies. The management followed standard care protocols, including robotic transanal surgery, despite the patient's ongoing HCC treatment. This case adds to the limited existing literature on SCCR, particularly its rare association with a tubulovillous adenoma. It emphasizes the importance of a multi-disciplinary approach in diagnosing and managing rare entities in colorectal cancer while demonstrating the feasibility of standard care in patients with complex comorbidities.