Low-Grade Fumarate Hydratase-Deficient Renal Cell Carcinoma in a 30-Year-Old Female.

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and clinically aggressive RCC subtype that is commonly associated with the hereditary leiomyomatosis and renal cell carcinoma syndrome. The diagnostic hallmark of FH-deficient RCC is a high-grade microscopic appearance with prominent inclusion-like eosinophilic nucleoli and perinucleolar halos. Herein we report a case of an FH-deficient RCC in a 30-year-old female that exhibited low-grade nuclei and abundant eosinophilic cytoplasm, reminiscent of the clinically more indolent succinate dehydrogenase-deficient RCC subtype and the newly described eintity, eosinophilic, solid and cystic RCC. This case illustrates that FH-deficient RCC can have a wide spectrum of microscopic appearances, including low-grade eosinophilic RCC. In addition, it highlights that a low threshold to perform the immunohistochemical stains for FH and S-(2-succino) cysteine is warranted in RCC cases with unusual and even low-grade eosinophilic morphology.