Eosinophilic variant of chromophobe renal cell carcinoma metastasizing to the liver: Diagnostic pitfall

An 82-year-old man developed a hypervascular renal tumor, 2 cm in size, and multiple liver tumors. Liver tumors had obscured tumor margins on ultrasonography. Positron emission tomography/computed tomography (PET/CT) showed no areas of avid radiotracer uptake in the liver. Routine pathological examination failed to demonstrate tumor cells in 9 tissue samples obtained from repeated core needle biopsies. Even a frozen section of the liver segment 8 tumor further failed to prove malignant cells, and an additive frozen section of the liver section 2 tumor finally proved atypical cells growing in tubular and solid fashions with eosinophilic cytoplasm. Tumors showed expansive growth patterns, were in direct contact with normal liver cells, had abundant micro-vessels, had only sparse hyalinized septa, and had no pale cells. Immunostaining revealed the tumor cells to be positive for CD10, CD117, and E-cadherin and negative for CK7, and PAX8, leading to the diagnosis of metastatic chromophobe renal cell carcinoma (chRCC) in the liver. Arginase-1 immunostaining clearly demarcated the boundary between the chRCC cells and normal hepatic cells. Diagnostic physicians should note that chRCCs are of low-grade malignancy despite their abundant intra-tumoral blood flow and can often pose imaging and pathologic diagnostic difficulties.