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

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.