# A Rare Case of Extra-renal Clear Cell Renal Cell Carcinoma

## TL;DR

A rare case of kidney cancer outside the kidney is reported in a 75-year-old man, highlighting the importance of accurate diagnosis.

## Contribution

This paper presents a rare clinical case of extra-renal clear cell renal cell carcinoma and emphasizes its diagnostic challenges.

## Key findings

- A 75-year-old male had a mass in the right iliac fossa diagnosed as extra-renal clear cell RCC.
- The diagnosis was confirmed through pathology and PET/CT scans showing no primary kidney tumor.
- Extra-renal RCC is extremely rare and likely originates from embryonic mesodermal remnants.

## Abstract

Renal cell carcinoma (RCC) is the predominant solid lesion found in the kidney. Extra-renal RCC is a rare entity. We present the case of a 75-year-old male with an incidentally discovered mass in the right iliac fossa. The patient underwent active surveillance because a percutaneous biopsy revealed a mesenchymal neoplastic lesion of benign biological behavior. As the mass had high growth rates, a decision for open surgical exploration and excision was made. The pathology results indicated clear cell renal carcinoma, and negative results on 18F-FDG whole-body positron emission tomography-computed tomography (PET/CT) established the diagnosis of extra-renal clear cell RCC. Similar types of neoplasms are extremely rare and are estimated to have developed primarily in mesodermal embryonic remnants. Clinicians should be aware of this rare entity as its diagnosis is challenging and is based on pathology.