Clinical Outcomes and Therapeutic Response in Adult TFE3-Related Renal Cell Carcinoma: A Case Series From a Tertiary Cancer Center in Southern India.

TFE3-rearranged renal cell carcinoma (TFE3-RCC) is a rare molecular subtype of renal cell carcinoma (RCC), characterized by Xp11.2 translocations involving the TFE3 gene. It is more common in pediatric populations and is often associated with aggressive clinical behavior and diagnostic challenges. Given the rarity of this entity in adults and limited therapeutic evidence, institutional case series remain valuable to enhance understanding of its clinicopathologic spectrum and outcomes. We conducted a retrospective case series of four adult female patients diagnosed with TFE3-rearranged RCC at a tertiary cancer center. Diagnosis was established based on morphology and strong nuclear TFE3 immunoreactivity, supported by additional immunohistochemical (IHC) markers including cluster of differentiation 10 (CD10), Melan-A, human melanoma black 45 (HMB45), vimentin, carbonic anhydrase IX (CAIX), and cytokeratins. Clinical presentation, radiologic findings, histopathologic features, immunohistochemical (IHC) profile, treatment modalities, and outcomes were reviewed. The median age was 32 years (range: 22-51). Two patients presented with localized stage III disease and underwent surgical resection (partial or radical nephrectomy), remaining disease-free at six months and one year of follow-up. Two patients presented with stage IV metastatic disease. One patient experienced late metastatic recurrence seven years after initial nephrectomy and is currently on cabozantinib with stable disease. The other had widespread metastases with spinal cord compression and showed disease progression despite targeted therapy and palliative radiotherapy, ultimately succumbing to the disease. Morphologically, tumors demonstrated heterogeneous features including clear cell, papillary, epithelioid, oncocytic, and melanotic differentiation. One case with coarse melanin pigmentation mimicked perivascular epithelioid cell tumor (PEComa), highlighting diagnostic complexity. TFE3-rearranged RCC in adults demonstrates heterogeneous morphology and variable clinical behavior, ranging from favorable outcomes in localized disease to aggressive progression in metastatic settings. Accurate diagnosis requires a high index of suspicion and comprehensive IHC evaluation, particularly in tumors with atypical morphology or melanotic differentiation. Advanced disease shows unpredictable response to targeted therapy, underscoring the need for further molecular characterization and prospective studies to optimize management strategies. Long-term surveillance remains essential due to the risk of late recurrence.