TFE3-rearranged and TFEB-altered renal cell carcinoma: from classification to real-life. Insights from a national Italian survey

Objective: Ongoing discoveries in cancer research keep expanding the landscape of renal cell carcinoma classification, particularly for "molecularly-defined" tumors like TFE3-rearranged and TFEB-altered renal cell carcinoma. However, scientific updates often do not align with pathologists' daily practice and resources. Herein, we present the results from a national Italian survey assessing physicians' personal experience on TFE3-rearranged and TFEB-altered renal cell carcinomas. Methods: An online questionnaire encompassing 26 questions was delivered to the Italian Study Group of Uropathology (GIUP) members, addressing critical concerns on their routine approach to these tumors. The answers were collected and further analyzed. Results: Thirteen pathologists with varying uropathological experience responded to the survey. Data confirmed the rarity of these neoplasms, with 69% of participants experiencing fewer than five or none at all. Despite this, aggressive behavior was documented by half of the respondents. Unusual morphology (62%) and young age (38%) were identified as the most relevant clues for suspecting TFE3-rearranged and TFEB-altered renal cell carcinoma. However, variability was observed in the specific histological features and the age threshold. The majority of the participants (54%) agreed on the need for ancillary molecular techniques for diagnostic purposes. Regarding immunohistochemistry, all professionals relied on multiple assays, attributing a primary role to a panel including cathepsin K, melanocytic markers (HMB45 and melan-A), PAX8, cytokeratin 7, and CA9. Additionally, most (58%) reported routine TFE3 immunohistochemical staining, although generally considering it reliable as long as diffuse and intense (58%) or requiring FISH confirmation in every positive case (25%). As for this latter, variability was recorded regarding split-signals positivity cut-off. Conclusions: The continuous evolution of renal cell carcinoma classification significantly impacts the pathologists' routine approach. Our survey underscores the importance of ongoing knowledge sharing and heightened awareness for accurately identifying TFE3-rearranged and TFEB-altered renal cell carcinoma and providing further insights on still unsolved issues.