# Metastatic Prostate Ductal Adenocarcinoma Presenting as a Solitary Rectal Mucosal Polyp: A Case Report

## TL;DR

A rare case of prostate cancer metastasizing to the rectum is reported, emphasizing the importance of accurate diagnosis using immunohistochemistry.

## Contribution

This case report highlights the unusual presentation of metastatic prostate ductal adenocarcinoma in the rectum and its diagnostic challenges.

## Key findings

- Metastatic prostate ductal adenocarcinoma presented as a solitary rectal mucosal polyp in a post-prostatectomy patient.
- Immunohistochemistry was crucial for distinguishing metastatic prostate cancer from rectal adenocarcinoma.
- Local recurrence occurred after surgical removal, necessitating radiation therapy.

## Abstract

While prostate cancer is predominantly of the acinar subtype, ductal adenocarcinoma is a rare variant that typically presents at an advanced stage, often with low prostate-specific antigen (PSA) levels and rare gastrointestinal metastases. We report the case of a 75-year-old male patient with a history of prostate cancer status post-prostatectomy who, during routine surveillance, exhibited a solitary rectal mucosal polyp. Imaging and colonoscopy identified an invasive carcinoma, mimicking rectal adenocarcinoma, but histologically and immunohistochemically consistent with metastatic prostate ductal adenocarcinoma, isolated to the rectum without other site involvement. The metastatic tumor was surgically removed initially, but local recurrence occurred within a year, and the recurrent tumor was treated with radiation therapy due to inoperability. This case highlights the need to consider metastatic tumor in a patient with a previous history in the differential diagnosis of solitary colorectal lesions and underscores the role of immunohistochemistry in accurate diagnosis and management.