[Clinicopathological and molecular characteristics of renal cell carcinomas with TFEB gene amplification]

Objective: To investigate the clinicopathological characteristics, molecular features, differential diagnosis and prognosis of renal cell carcinoma (RCC) with TFEB gene amplification. Methods: A total of 113 cases of unclassified RCCs and RCCs with TFEB positive expression were collected from the Affiliated Hospital of Qingdao University and Navy 971 Hospital from January 2010 to December 2024. Eight cases of RCCs with TFEB amplification were identified using tissue microarrays, immunohistochemistry, and fluorescence in situ hybridization (FISH) techniques. The clinicopathological data and prognosis of the 8 cases were summarized, and relevant literature was reviewed. Results: Among the 8 cases, there were 5 males and 3 females. The average age was 63.4 (54, 77) year and the median age was 63.5 (59.0, 65.5) year. Seven cases were detected through physical examination, and 1 case presented with initial symptoms of metastasis to bones and lungs. The cohort included 1 biopsy specimen and 7 surgical resection specimens. The tumor diameters ranged from 2.5 to 15.0 cm. The cut surfaces of 5 cases were grayish-yellow or grayish-red, and 2 cases exhibited a colorful appearance, among which 3 cases involved renal sinus and 1 case showed invasion of the perirenal fat tissue. Microscopically, 4 cases were composed of clear cells arranged in solid sheets or acinar structures, along with varying numbers of eosinophilic cells. Two cases exhibited the morphology of high-grade eosinophilic RCC, and 1 case presented biphasic morphology with diffuse polygonal eosinophilic tumor cells and dense small cell components. The remaining 1 case exhibited the morphology of clear cell RCC. According to the WHO/ISUP nuclear grading system, 6 cases were Grade 3 and 2 cases were Grade 2. Multifocal necrosis was observed in 4 cases. In 4 surgical specimens, the tumor tissue invaded the renal parenchyma, with 2 cases showing nodular infiltration to surrounding tissues and 1 case with intravascular tumor thrombus. Immunohistochemical results showed varying degrees of TFEB nuclear positivity in 6 cases (6/8). Melanocytic markers such as Melan A (5/8) and HMB45 (3/8) were expressed at varying degrees. Cathepsin K (6/8), GPNMB (6/8), P504s (7/8) and CD10 (7/8) were positively expressed in most cases. FISH results revealed high-copy amplification of TFEB gene in 4 cases (partially showing clustered amplification) and low-copy amplification in 4 cases. During the follow-up period of 3 to 64 months of the 8 cases, 3 cases metastasized and 2 cases died of disease (both with high-copy TFEB gene amplification). Conclusions: RCC with TFEB gene amplification is rare and exhibits diverse morphological features. A common morphological characteristic of this type of tumor is a mixture of sheet-like clear cells and high nuclear grade eosinophilic cells. Combined immunohistochemical staining for TFEB, melanocytic markers, and GPNMB is helpful for the diagnosis of the tumor, and FISH detection of TFEB gene amplification is the most definitive method in diagnosing this tumor. RCC with TFEB gene amplification usually presents with strong aggressiveness and poor prognosis. Combining surgical resection with immunotherapy or VEGFR-targeted drugs might have therapeutic effects on the tumor.