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case_images: Representative CT images of TFE3-rearranged RCC patients. (A) High-density lesions with scattered calcifications (arrows) in the lower pole of the left kidney were observed on plain scan; cystic-solid suspicious metastases (triangles) were observed in the retroperitoneum. (B) Moderate enhancement of the left renal lesion and suspicious metastases was observed during the enhanced phase, and the degree of enhancement was lower than that of the adjacent renal cortex. (C) Lesions and metastases were significantly reduced after neoadjuvant therapy. (D) Postoperative reexamination showed no recurrence of tumor metastasis.
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case_images: A computed tomography (CT) scan revealed a solid-cystic tissue density lesion with calcification measuring 3.2 x 2.8 cm at the ventral middle and lower poles of the left kidney ( Figure 1A ). The solid component demonstrated moderate enhancement in the corticomedullary phase ( Figure 1B ). After 8 months of neoadjuvant therapy, the tumor and metastasis sizes decreased by 16% (3.2 x 2.8 cm vs. 2.7 x 2.4 cm) and 30% (4.6 x 2.4 cm vs. 3.2 x 2.2 cm), respectively, compared to their original sizes ( Figure 1C ). As of now, the patient has survived for 30 months post-surgery and remains in stable condition without any recurrence of tumor or distant metastases ( Figure 1D ).
case_images: (A, B) Pathology of left renal needle biopsy, papillary cells arrangement, marked cellular eosinophilia (H&E, Ax 200, Bx800). (C) TFE3 overexpression (x200). (D) Positive for PAX8 (x200). (E) Tumor cells have split signals in fluorescence in situ hybridization analysis. One yellow fused signal, one pair of red-green separated signals can be seen. (F) Positive for PDL1 (x200).
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case_images: Therefore, a left renal puncture biopsy was performed, and the pathology morphology was examined using hematoxylin-eosin (HE) staining, which revealed hyaline eosinophilic cytoplasm with papillary structures and psammoma bodies ( Figures 2A, B ). Additionally, strong positive nuclear immunohistochemical staining of TFE3 was observed ( Figure 2C ). Immunohistochemically, negative results were observed for CAIX, CK7, and ALK, while CD10 and PAX8 are positive ( Figure 2D ). TFE3 break-apart FISH was performed, which confirmed the diagnosis of TFE3-rearranged RCC ( Figure 2E ). To further clarify the molecular type, targeted next-generation sequencing was performed, and the final diagnosis of ASPSCR1-TFE3 fusion translocation RCC was confirmed ( Figure 3 ).
case_images: A fusion of TFE3 and ASPSCR1 was detected in the tumor.
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case_images: TFE3 break-apart FISH was performed, which confirmed the diagnosis of TFE3-rearranged RCC ( Figure 2E ). To further clarify the molecular type, targeted next-generation sequencing was performed, and the final diagnosis of ASPSCR1-TFE3 fusion translocation RCC was confirmed ( Figure 3 ).
case_images: Postoperative pathological view. (A) Specimens of masses (x100). (B) Retroperitoneal metastases (x200).
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case_images: The postoperative pathology revealed that the tumor was WHO/ISUP grade 4, and it appeared as a distinct papillary structure ( Figure 4A ). The HE staining confirmed that the metastatic foci were composed of tumor tissues ( Figure 4B ).
case_images: The patient systemic therapy timeline.
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case_images: The systemic therapy timeline is presented in  Figure 5 .