Case 109

A 67 year old male with a 7.9 cm heterogenous right kidney mass.

1. What's your diagnosis?

   A: Papillary renal cell carcinoma

   B: Clear cell papillary tumor

   C: Clear cell carcinoma

   D: Chromophobe renal cell carcinoma

Answer

The correct answer is A. This tumor is positive for AMACA and negative for CK7.

• Architectural Pattern:

  • Papillary and tubular structures.

  • Lined by cuboidal cells with scant or lightly basophilic cytoplasm.

  • Basophilic appearance at low power.

• Common Ancillary Features (not diagnostic requirements):

  • Foamy histiocytes.

  • Psammoma bodies [PMID: 9199639].

  • Variable cytoplasm:

    • Clear/vacuolated [PMID: 18779729, 21074210].

    • Eosinophilic/voluminous.

    • Haemosiderin pigmentation [PMID: 11169884, 2065568].

      
      

Morphological Variants

• Solid architecture (can obscure papillary growth) [PMID: 27209513].

• Clear/vacuolated cells mimicking CCRCC [PMID: 18779729, 21074210].

• Biphasic pattern: squamoid cells in glandular lumina [PMID: 29119638, 26999503].

• Brisk inflammation: may mimic Warthin tumour [PMID: 28325361].

  
  

Papillary Neoplasm with Reverse Polarity

• Thin, branching papillae.

• Low-grade oncocytic cells with apically aligned nuclei.

• IHC Profile:

  • GATA3: positive.

  • Vimentin: negative.

  • AMACR: variable or focal.

  • CAIX: negative/focal (vs. strong in CCRCC).

• Molecular Feature: Recurrent KRAS mutations.

• References: [PMID: 17949780, 31534204, 31135486, 32403965, 31997427, 31953522, 28984673].

• Immunohistochemistry

• AMACR (P504S): strong diffuse positivity (regardless of subtype).

• CK7: usually positive, decreased in eosinophilic tumours [PMID: 9195569].

• CD10, Vimentin: often positive.

• CAIX: negative or focal (vs. diffuse in CCRCC).

Case credit: UCSD pathology

Author: Wangpan Jackson Shi, MD