[Clinicopathological and molecular characteristics of primary renal Ewing sarcoma: an analysis of seventeen cases].

Objective: To investigate the clinicopathological and molecular characteristics of primary renal Ewing sarcoma. Methods: Seventeen cases of primary renal Ewing sarcoma were collected, diagnosed from January 2011 to May 2023 at Peking University Third Hospital (11 cases), Peking University Institute of Urology (4 cases), and Peking University Cancer Hospital (2 cases). The clinical, histopathological, and molecular features were studied using HE staining, immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and targeted next-generation sequencing (NGS). The prognostic correlations were assessed. Results: The cohort included 9 males and 8 females, aged 32 (24, 46) years. Presenting symptoms included hematuria and lumbar pain (13/17), right lower limb/buttock edema (1/17) and persistent low fever (1/17), and other two cases were incidentally detected by imaging in physical examination. All tumors showed renal venous/inferior vena cava tumor thrombosis and were treated with radical nephrectomy and thrombectomy. The tumor maximum diameters were 13.0 (9.0, 15.5) cm. Histologically, tumors showed morphology of diffuse sheets of small round cells with indistinct borders, round nuclei, fine chromatin, and frequent mitoses. Focal rosette-like structures were identified. The morphological heterogeneity was noted in 11 cases, including short spindle-shaped cells, gland-like structure formations, and hemangioma-like patterns. Renal pelvis invasion (5/17) and perirenal fat involvement (10/17) were identified. Immunohistochemistry showed diffuse positive for CD99 (17/17) and NKX2.2 (12/12), while FLI1 was positive in 6/12. Ki-67 indices ranged from 5% to 85%. FISH results confirmed EWSR1 rearrangement in all cases, and NGS (6/17) validated EWSR1-FLI1 fusions. Follow-up (3-84 months; 13/17) revealed metastases in 6 patients (adrenal gland, liver, bone, lung and peritoneum; 3-36 months post-surgery), of which 2 patients died, 1 patient with unknown time of death. The other 6 patients remained disease-free. All the metastatic cases showed elevated Ki-67 index (50%-70%) and necrosis. Conclusions: Primary renal Ewing sarcoma is an aggressive malignant tumor, often diagnosed at advanced stages with venous tumor thrombosis. The morphological heterogeneity and high rate of hemorrhage and necrosis are correlated with more invasive potential, suggesting prognostic significance.