[CK7+/CD117- low grade oncocytic tumor of the kidney: a clinicopathological analysis]

Objective: To investigate the clinicopathological, immunohistochemical and molecular characteristics of low grade oncocytic tumors (LOT) of the kidney with CK7+/CD117- staining pattern for enhancing the understanding of renal LOT. Methods: The clinical data, histological morphology and immunophenotypes of seven renal LOT cases diagnosed at the Department of Pathology, the First Affiliated Hospital, Zhejiang University School of Medicine from January 2017 to April 2021 were analyzed. The patients were followed up. Among the seven patients, five underwent high-throughput DNA targeted sequencing, and their molecular characteristics were analyzed. Results: The patients' age ranged 59-82 years, with an average of 70 years. There were 2 males and 5 females. The boundary of the tumor was clear. The tumor cells had homogeneous eosinophilic cytoplasm and round or oval nuclei, with a perinuclear halo. Small basophilic nucleoli were conspicuous (WHO/International Society of Urological Pathology grade 2). In the hypercellular areas, the tumor cells were mainly arranged in dense solid or nest. In the stroma, there were dilated veins, thick-walled arterioles and thick collagen fiber bundles that divided the cells into pseudonodules. In the sparsely cellular area, the tumor cells were arranged in the so-called "tissue culture" fashion. In addition, the stroma contained fresh hemorrhagic foci and lymphoid aggregates. High-throughput sequencing of 5 cases revealed that one case harbored mTOR gene missense mutation and another case harbored TSC1 frameshift mutation. Conclusions: LOT of the kidney is an indolent tumor with an overall good prognosis. Pathologists should not misdiagnose it as renal oncocytoma and chromophobe renal cell carcinoma.