Fumarate Hydratase-Deficient Renal Cell Carcinoma With Predominant Tubulocystic Features Mimics Tubulocystic Renal Cell Carcinoma

* Context.--Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) rarely exhibits a predominant tubulocystic architecture with few other components. RCC with pure tubules and cysts lined by eosinophilic tumor cells with prominent nucleoli would raise the diagnosis of tubulocystic RCC. It is important to differentiate the 2 entities because they lead to different outcomes. Objective.--To address this concern, a multicenter study was implemented to explore useful clinicopathologic features in differentiation between tubulocystic FH-deficient RCC and tubulocystic RCC. Design.--Clinical factors included age, sex, tumor size, and outcome. Morphologic factors included cell morphology, presence or absence of a nontubulocystic component, and stromal findings. Immunohistochemistry, fluorescence in situ hybridization, and next-generation sequencing were performed to explore the protein expression and molecular profiles of the 2 entities. Results.--We evaluated 6 patients with tubulocystic RCC and 10 patients with tubulocystic FH-deficient RCC. Tubulocystic RCC exhibited a small size ( Conclusions.--We emphasized multiple sectioning to identify a nontubulocystic architecture to exclude tubulocystic RCC. Moreover, tumor size, FH/2SC staining, and the Ki-67 index can differentiate tubulocystic FH-deficient RCC from tubulocystic RCC. The diagnosis of tubulocystic RCC was not recommended in renal mass biopsy because of the limited tissues sampled. (Arch Pathol Lab Med. 2024;148:1358-1364; doi: 10.5858/arpa.2023-0330-OA)
Molecular studies have expanded our knowledge of renal cancers. The 5th edition of the World Health Organization (WHO) updated new developments in existing and novel renal entities. (1) Tubulocystic renal [...]