MTOR-mutated eosinophilic renal cell carcinomas with loss of chromosome 1 and high metastatic potential: further expanding the spectrum of TSC/mTOR pathway mutated renal tumors

TSC/mTOR pathway alteration is recurrent in numerous renal tumor types, such as eosinophilic vacuolated tumor (EVT), low-grade oncocytic tumor of the kidney (LOT), and eosinophilic solid and cystic (ESC) renal cell carcinoma (RCC). Recently, additional renal tumor types with recurrent TSC/mTOR pathway mutation, such as xanthomatous giant cell RCC and RCC with leiomyomatous stroma, have also been described, further expanding the spectrum of renal tumors with TSC/mTOR pathway mutation. To this date, most renal tumors with TSC/mTOR pathway mutation are reported to be mostly indolent, with only rare cases of metastasis. However, this report describes two cases (one of which was previously published as a case report) of MTOR-mutated eosinophilic RCCs with loss of chromosome 1. The tumors mostly exhibit solid/nested and sheet-like growth patterns composed of tumor cells with plump eosinophilic cytoplasm, with occasional vacuolation, pronounced cellular membrane, and occasional perinuclear clearing. The tumor cells showed prominent nucleoli and round nuclei with smooth nuclear membrane. The tumor had occasional binucleated tumor cells with rhabdoid morphology, areas with prominent hyalinized stroma and psammomatous calcification, and tumor cells with blue granules. Immunohistochemistry showed that the tumors were diffusely positive for CD117 and negative for vimentin, and negative for CK7, Melan A, and TFE3. CK20 was positive in both tumors, with diffuse expression in one and focal expression in the other. Next-generation sequencing showed concomitant MTOR mutation and loss of chromosome 1. Both tumors displayed metastatic potential. Overall, these MTOR-mutated eosinophilic RCCs with loss of chromosome 1 have distinct morphologic, immunohistochemical, and molecular features as well as high metastatic potential, further expanding the spectrum of TSC/mTOR pathway-mutated renal tumors. This tumor requires further investigations due to its high metastatic potential that is infrequently observed in other TSC/mTOR pathway-mutated renal tumors and the potential therapeutic target it may offer in mTOR inhibitor.