Sclerosing TSC1 Mutated Renal Cell Carcinoma: An Unusual Pattern Mimicking MITF Family Translocation Renal Cell Carcinoma.

: The tuberous sclerosis genes and MTOR are increasingly being found to have important roles in novel subtypes of renal cancer, particularly emerging entities eosinophilic solid and cystic renal cell carcinoma (RCC) and high-grade oncocytic renal tumor (HOT) / RCC with eosinophilic and vacuolated cytoplasm. We report a unique renal neoplasm in a 66 year-old woman that initially mimicked MITF family translocation RCC due to mixed clear and eosinophilic cells, extensive stromal hyalinization, and psammoma bodies, yet which was negative for TFE3 and TFEB fluorescence in situ hybridization (FISH) and a next generation sequencing (NGS) gene fusion assay. Cytoplasmic stippling triggered consideration of TSC-associated neoplasms, and a targeted next generation sequencing assay revealed a variant in exon 21 of TSC1 resulting in c.2626G > T p.(Glu876*) truncating mutation. This report adds to the morphologic spectrum of TSC-related renal neoplasms, including prominent stromal hyalinization as a potentially deceptive pattern. Due to the overlap in cytoplasmic stippling between eosinophilic solid and cystic RCC and HOT / RCC with eosinophilic and vacuolated cytoplasm, it is debatable which category this example would best fit. Further understanding of these entities and other renal neoplasms with alterations in the TSC genes will elucidate whether they should be considered a family of tumors. This article is protected by copyright. All rights reserved.