60-year-old man with sudden weight loss   

Findings and diagnosis

Microscopic findings

Sections from the kidney show eosinophilic cells arranged in nests, divided by incomplete septa. On higher magnification, cells show hyperchromatic nuclei with perinuclear halos and eosinophilic acellular material in the cytoplasm. There are focal areas with spindle cell proliferation due to sarcomatoid differentiation.

Differential diagnosis

  • Oncocytoma 
  • Hybrid oncocytic tumor
  • MiTF translocation renal cell carcinoma  
  • Low-grade oncocytic tumor
  • Clear cell carcinoma with eosinophilic features
  • Chromophobe renal cell carcinoma

Diagnosis: Chromophobe renal cell carcinoma (RCC)