Tubulocystic Renal Cell Carcinoma With Pure Morphology and Confirmed "Wild Type" FH/2SC Immunophenotype: Clinicopathologic Series of 30 Patients.

Tubulocystic renal cell carcinoma is a rare neoplasm, first adopted into the WHO classification of kidney tumors in 2016. The diagnostic criteria were refined in the 2022 WHO classification, requiring "pure morphology" and exclusion of other renal cell carcinoma subtypes with overlapping features. We identified 31 tubulocystic renal cell carcinomas from 30 patients. Median age was 60 years (30 to 77 y) with male:female ratio of 13.5:1. Race was known for 26 patients, and the majority were African American (n = 16/26,62%), followed by white/Caucasian (10/26, 38%). Eleven patients (37%) had a history of chronic or end-stage renal disease. Median tumor size was 2.3 cm (range: 0.4 to 6.3 cm). All tumors were characterized by cysts and tubules, surrounded by fibrotic stroma. Lining epithelial cells had eosinophilic cytoplasm, ranging from flattened to cuboidal to hobnail in arrangement. By definition, solid epithelial nodules and destructive invasion were absent. In addition, all tumors had a normal pattern of FH and 2SC expression by immunohistochemistry. AJCC stage was pT1 for all 31 tumors: 30 pT1a and 1 pT1b. All patients had no evidence of disease at last follow-up (median: 35 mo; range: 1 to 294 mo). We report a large series of tubulocystic renal cell carcinomas with pure morphology and confirmed normal/"wild type" FH/2SC immunophenotype. When these strict definitions are applied, our findings confirm an indolent clinical behavior.