Abstract

Background: Eosinophilic solid and cystic renal cell carcinoma (ESC RCC) is a rare renal tumor entity recently recognized in the World Health Organization classification of urinary system tumors. It predominantly affects middle-aged women and demonstrates distinctive morphologic and immunohistochemical features. Case presentation: A 49-year-old woman presented with a Bosniak IV cystic mass in the right kidney. Gross examination revealed a 5.5 cm tumor composed of solid and cystic areas with hemorrhagic content. Microscopically, tumor cells showed abundant eosinophilic granular cytoplasm and round nuclei, arranged in solid and cystic patterns. The cystic spaces frequently contained red blood cells, with focal hobnail-like epithelial lining. Immunohistochemistry demonstrated positivity for PAX8, cytokeratin, CD10, and vimentin, while CK7, CK20, RCC marker, EMA, and CD117 were negative. The Ki-67 proliferation index was approximately 2%. Conclusion: The clinicopathologic findings support the diagnosis of eosinophilic solid and cystic renal cell carcinoma. Accurate recognition is important to avoid misdiagnosis with other eosinophilic renal tumors.