Cytomorphology and clinicopathologic correlation of TFE3-rearranged renal cell carcinoma.

Background: TFE3-rearranged renal cell carcinoma (TFE3-rRCC) harbors gene fusions involving TFE3 with one of many different partner genes. Because of their diverse morphologies, the differential diagnosis is broad and challenging. Publications focusing on the cytomorphology of TFE3-rRCC are sparse.

Methods: Fifteen cytology cases of TFE3-rRCC from 12 patients were retrieved, comprising seven primary kidney cases and eight metastatic cases.

Results: Cytology smears showed tumor cells with moderate granular or vacuolated cytoplasm, arranged in diverse patterns, such as three-dimensional clusters, nested/sheeted formations, isolated cells, papillary, and tubular/acinar structures. The tumor cells exhibited enlarged eccentric, round or oval nuclei, possibly situated peripherally, with small to prominent nucleoli and irregular nuclear membranes. Macrophages, hyalinized globules, or necrosis were occasionally seen. Core and cell block histology often showed papillae with surface-oriented nuclei. Tumor cells were also arranged in nested, sheeted, and tubular patterns. Tumor cells were immunoreactive to TFE3 (100%), AMACR (100%), PAX8 (88%), and CD10 (83%) and showed focal staining for CA9 (64%), CK7 (20%), and CD117 (25%). TFE3 rearrangement was confirmed in 13 of 15 cases through fluorescence in situ hybridization or RNA fusion next-generation sequencing testing. Metastasis was observed in nine of 12 patients (80%), with retroperitoneal lymph nodes being the most common site, followed by distant lymph nodes, lung, brain, adrenal gland, and bone. Six patients (50%) underwent nephrectomy alone, two patients (17%) received chemotherapy alone, and four patients (33%) received combined nephrectomy and chemotherapy.

Conclusions: Timely recognition of TFE3-rRCC's distinct cytomorphologic and histomorphologic features is essential for accurate diagnosis and effective treatment.