Re-evaluation of 33 “Unclassified” Eosinophilic Renal Cell Carcinomas in Young Patients

Abstract

Aims

We sought to determine if some unclassified renal cell carcinomas (RCCs) in children and young adults that are characterized by predominantly eosinophilic cytoplasm are related to the recently described succinate dehydrogenase (SDH)-deficient RCC, fumarate hydratase (FH)-deficient RCC, or eosinophilic solid and cystic (ESC) RCC.

Methods and Results

We reviewed 33 unclassified RCCs with predominantly eosinophilic cytoplasm in patients age 35 years or younger. Immunohistochemistry (IHC) for SDHB, FH, and CK20 (a marker of ESC) was performed on all cases. IHC for 2-succinocysteine (2SC) was performed on RCC with loss of FH labeling. Four RCC (12%) (median age 18 years) demonstrated loss of FH labeling as well as aberrant 2SC labeling, and thus were classified as FH-deficient RCCs. Importantly, none of these cases demonstrated the characteristic macronucleoli typical of FH-deficient RCC. Eight RCC (24%) (median age 20.5 years) demonstrated loss of SDHB and were reclassified as SDH-deficient RCCs. Importantly, only four of eight SDH-deficient RCC demonstrated the characteristic cytoplasmic vacuoles and inclusions of typical SDH-deficient RCC. Ten RCC (30%) (median age 27 years) were reclassified as ESC RCCs. Four of ten ESC RCC were multifocal (1 bilateral), four of ten ESC RCC occurred in males, and one patient presented with liver and lung metastases, all not previously described in ESC. Eleven RCC (33%) remained unclassified.

Conclusions

Pathologists should have low threshold for performing FH, SDHB, and CK20 IHC when confronted with unclassified eosinophilic RCC or "oncocytoma" in young patients.

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