Kidney tumor

• Uncommon neoplasm composed of variable cystic and solid components with morphologically diverse epithelial and stromal elements
• Classified as part of MEST family, with adult cystic nephroma at opposite end of spectrum, by the 2016 World Health Organization (WHO) classification

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Contributed by Bonnie Choy, M.D.

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• Stroma:
  • SMA: strong and diffuse, 97% (Am J Surg Pathol 2000;24:958, Virchows Arch 2004;445:359, Am J Surg Pathol 2016;40:1538)
  • Desmin and caldesmon: more variable, focal to diffuse, 89% and 88%, respectively (Am J Surg Pathol 2000;24:958, Virchows Arch 2004;445:359, Am J Surg Pathol 2016;40:1538)
  • ER and PR: 88% and 95%, respectively (Am J Surg Pathol 2000;24:958, Virchows Arch 2004;445:359, Am J Surg Pathol 2016;40:1538)
  • CD10: often concentrated around epithelial elements, 90% (Am J Surg Pathol 2016;40:1538)
  • Inhibin and calretinin: in ovarian type stroma, particularly in luteinized cells (Am J Surg Pathol 2007;31:489)
  • FOXL2: in ovarian type stroma, 90% (Hum Pathol 2014;45:1010)
• Epithelium:
  • Cytokeratins
  • PAX2, PAX8 (Am J Surg Pathol 2011;35:1264)
  • GATA3: coexpression with PAX8, 57% (Am J Surg Pathol 2016;40:1538)

• Adult cystic nephroma:
  • Part of the MEST family, with MEST at opposite end of spectrum, on basis of comparable clinical features (sex and age distribution), overlapping morphologic findings and similar immunohistochemical profile
  • No solid component
  • Multilocular cysts lined by flat, hobnail or columnar epithelium
  • Fibrous septae with ovarian-like stroma in areas
• Angiomyolipoma with epithelial cysts (Am J Surg Pathol 2006;30:593):
  • Overlapping histologic features
  • Stromal component positive for melanocytic markers, HMB45 and MelanA
• Renomedullary interstitial cell tumor (Hum Pathol 2018;82:46):
  • Almost always incidentally found in kidney resection for other causes
  • Characteristically small size (usually < 5 mm), rare larger tumors
  • Peripherally to diffusely entrapped renal tubules
  • Commonly positive for ER and PR (61%) but typically weak
• Metanephric adenofibroma:
  • Usually occur in infancy and early childhood
  • Epithelial component composed of tightly packed, small, uniform acini, with embryonal appearance
  • Stroma negative for SMA, desmin, ER and PR
• Cystic partially differentiated nephroblastoma:
  • Most occur in patients < 24 months old
  • Nephroblastematous tissue (e.g. blastema, immature stromal cells, primitive epithelial elements) present
• Mesoblastic nephroma:
  • Negative for ER and PR
  • t(12;15)(p13;q25), resulting in ETV6-NTRK3 gene fusion, seen in cellular type
• Multilocular cystic neoplasm of low malignant potential:
  • Clusters or nests of clear cells present in cystic septa
  • No cellular stroma
• Papillary renal cell carcinoma with prominent spindle cell stroma (Ann Diagn Pathol 2020;44:151441):
  • Papillary and tubulopapillary architecture
  • Variable cytologic atypia
  • Stromal component negative for desmin, ER and PR
• Sarcomatoid renal cell carcinoma:
  • Infiltrative borders
  • Marked cytologic atypia
  • Necrosis and mitotic figures frequent
• Synovial sarcoma:
  • Most are monophasic type with entrapped renal tubules; biphasic type is rare
  • t(X;18)(p11;q11), resulting in SS18-SSX2 gene fusion

A 60 year old woman with hematuria was found to have a 3.5 cm variably cystic and solid renal mass on CT imaging. Partial nephrectomy showed a well circumscribed tumor with the above morphology. The stromal component is positive for ER and PR. What is the likely diagnosis?

1. Angiomyolipoma
2. Cystic partially differentiated nephroblastoma
3. Metanephric adenofibroma
4. Mixed epithelial and stromal tumor
5. Multilocular cystic neoplasm of low malignant potential

D. Mixed epithelial and stromal tumor

Mixed epithelial and stromal tumor is a well circumscribed, variably solid and cystic mass. Cystic partially differentiated nephroblastoma and metanephric adenofibroma typically occur in children. Multilocular cystic neoplasm of low malignant potential does not have a cellular stroma. None of the above choices, except for mixed epithelial and stromal tumor, demonstrate immunoreactivity for ER and PR.

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Reference: Mixed epithelial and stromal tumor

Which of the following is true about mixed epithelial and stromal tumor of the kidney?

1. Commonly bilateral and multiple
2. Harbor DICER1 gene mutations
3. Most behave in benign fashion
4. Typically occur in male patients

C. Most behave in benign fashion

Mixed epithelial and stromal tumor is typically seen in perimenopausal women. These tumors are solitary, with very rare exceptions. Most of these tumors have benign behavior following surgical resection. Unlike pediatric cystic nephroma, DICER1 gene mutations are not found in mixed epithelial and stromal tumor.

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Reference: Mixed epithelial and stromal tumor