[Clinicopathological features and diagnosis of pericytic tumors of the kidney]

Objective: To investigate the clinicopathologic features,diagnosis and prognosis of pericytic tumor of the kidney. Methods: Three cases of pericytic tumor of the kidney (two cases were diagnosed as glomangiomyomas and one case as pericytic tumor,unclassified) were collected from the affiliated Hospital of Qingdao University between January 2014 to May 2021; the clinical and morphologic features, immunohistochemical and molecular characteristics were analyzed and the relevant literature was reviewed. Results: The three patients included one male and two females, with ages ranging from 21 to 70 years. In two patients the tumors were detected incidentally at physical examination and one patient presented with low back discomfort. Imaging showed a rounded nodular soft tissue density shadow in renal parenchyma, and enhancement scan showed uneven delayed enhancement. Grossly, two tumors were located in the renal hilum and one in the renal parenchyma; all were nodular. The tumors were measured in size from 1.6 cm to 5.1 cm (mean 4.1 cm) and showed gray or gray-red cut surface. Histologic examination showed the tumor cells were arranged in solid sheets or small nodules, closely related to vascular wall. Tumor cells were mostly epithelial-like with abundant cytoplasm, light eosinophilia, obscure boundary and round nuclei with visible nucleoli. Vague bundles and fascicular arrangements of smooth muscle component were noted in some areas, with transition of both components. There was no necrosis. By immunohistochemistry, the tumor cells strongly and diffusely expressed vimentin, SMA and collagen Ⅳ, two cases expressed CD34, all three cases expressed PDGFRB to varying extent, and the Ki-67 index was 2%-3%. PCR tests showed absent K-RAS, BRAF V600E gene mutation in all three cases. PDGFRB mutations in exons 3 and 18, respectively were found in two of the three cases by high-throughput sequencing, and no NOTCH 1/2/3 gene fusions were found in any of them. Follow-up information (range: 6-92 months) showed no evidence of local recurrence or distant metastasis in all three patients. Conclusions: Pericytic tumor of the kidney is a rare mesenchymal tumor originating in the kidney with differentiation to smooth muscle, most commonly glomus tumor. The mild pleomorphism, close relationship with vascular wall and spindled smooth muscle components suggest the diagnosis of the tumor. Expression of both epithelial and muscle-associated markers aids the diagnosis. PDGFRB gene mutations may have an important role in the development of this tumor. Most patients have a good prognosis, and a few cases have malignant biological behavior.