MED15-TFE3 rearranged renal cell carcinoma: a subtype of TFE3-rearranged renal cell carcinoma with unique clinicopathologic features and better prognosis.

BACKGROUND: MED15-TFE3 rearranged renal cell carcinoma (MED15-TFE3 rRCC) is a rare subtype of TFE3-rearranged renal cell carcinoma (TFE3 rRCC). To date, only 47 cases of MED15-TFE3 rRCC (including 2 cases from our institution) have been reported worldwide. METHODS: Using immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and RNA sequencing, we aimed to identify whether TFE3 rRCC patients at our institution harbor the MED15-TFE3 gene fusion. We will perform a statistical analysis of the pathological features, imaging findings, and clinical outcomes of all published cases of MED 15-TFE rRCC. RESULTS: MED15-TFE3 rRCC typically has a cystic and solid (predominantly cystic) architecture. The tumor cells feature round nuclei with inconspicuous nucleoli, abundant cytoplasm, and clear to eosinophilic staining. Immunohistochemically, 38 of 39 patients had positive nuclear staining for TFE3, and 37 of 38 patients were positive for PAX8. The FISH assay was positive for rearrangement (red-green signal separation). RNA sequencing identified the MED15-TFE3 fusion gene. One pediatric patient presented with preoperative hilar lymph node metastasis. During follow-up, only one patient developed metastatic disease. CONCLUSIONS: In contrast to traditional TFE3 rRCCs, MED15-TFE3 rRCCs may have distinctive clinicopathological features and a better prognosis. These findings enhance our understanding of the heterogeneity of TFE3 rRCCs.