# Metastatic Clear Cell Renal Cell Carcinoma Identified in a Gastric Biopsy: Diagnostic Recognition in an Unusual Site

## TL;DR

A rare case of kidney cancer found in a stomach biopsy highlights the need for careful diagnosis in unusual locations.

## Contribution

Presents a rare case of metastatic ccRCC diagnosed via gastric biopsy before renal lesion sampling.

## Key findings

- Gastric biopsy showed epithelioid cells with clear cytoplasm and delicate vasculature.
- IHC staining confirmed renal origin with positivity for PAX8, RCC marker, and CD10.
- Negative staining for CK7, CK20, CDX2, and TTF-1 excluded primary gastrointestinal or pulmonary tumors.

## Abstract

Metastatic clear cell renal cell carcinoma (ccRCC) to the stomach is rare and may mimic other clear cell neoplasms when encountered in limited biopsy samples. We report a case in which a gastric biopsy provided the first histopathologic confirmation of metastatic ccRCC in a 65-year-old man who had not yet undergone tissue sampling of a suspected renal lesion. The biopsy showed nests of epithelioid cells with clear cytoplasm and delicate vasculature, and immunohistochemical (IHC) staining demonstrated strong positivity for paired box gene 8 (PAX8), renal cell carcinoma (RCC) marker, and CD10, supporting renal origin. Negative staining for cytokeratin 7 (CK7), cytokeratin 20 (CK20), caudal-type homeobox transcription factor 2 (CDX2), and thyroid transcription factor 1 (TTF-1) helped exclude primary gastric, gastrointestinal, and pulmonary neoplasms. Subsequent imaging confirmed a renal mass concordant with the IHC findings. This case underscores the importance of recognizing morphologic clues and using a targeted IHC panel when evaluating clear cell neoplasms in the gastrointestinal tract.