## Distinguishing Clear Cell from Papillary RCC ### Morphologic Hallmark **Key Point:** Clear cell RCC is defined by abundant intracytoplasmic **lipid and glycogen**, which is removed during routine processing, leaving the cytoplasm appearing clear or "empty" under light microscopy. This is the pathognomonic feature. ### Comparative Table | Feature | Clear Cell RCC | Papillary RCC | | --- | --- | --- | | **Cytoplasm** | Clear (lipid/glycogen-rich) | Granular, eosinophilic | | **Architecture** | Solid sheets, nests | Papillary/tubular structures | | **Stromal cells** | Delicate vasculature | Foamy macrophages prominent | | **Genetic basis** | VHL mutation (80–90%) | MET, TFEB mutations | | **CK7 staining** | Negative | Positive | | **Prognosis** | More aggressive (grade-dependent) | Generally better | ### High-Yield Points **High-Yield:** The clear appearance of cytoplasm in clear cell RCC is due to dissolution of lipid and glycogen during standard tissue processing. This is the single most reliable morphologic discriminator and is visible on routine H&E staining. **Clinical Pearl:** While both clear cell and papillary RCC can harbour VHL mutations, clear cell RCC has a much higher frequency (~80–90%), making it less discriminatory. Papillary RCC is more commonly associated with hereditary papillary RCC syndrome (MET mutations) and sporadic cases linked to TFEB translocations. ### Why This Matters **Tip:** On the NEET PG exam, when asked to distinguish RCC subtypes, always prioritize morphologic features visible on H&E staining (cytoplasmic appearance, architecture) over genetic associations, which may overlap. 
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