A subset of solitary fibrous tumors express nuclear PAX8 and PAX2: a potential diagnostic pitfall

Histol Histopathol. 2016 Feb;31(2):223-30. doi: 10.14670/HH-11-670. Epub 2015 Sep 26.

Abstract

Solitary fibrous tumor (SFT), a mesenchymal neoplasm with widespread anatomic distribution, can be diagnostically challenging in limited samples. We recently encountered an aspirate of a pancreatic mass, incorrectly interpreted as metastatic renal cell carcinoma based on strong PAX8 expression by immunohistochemistry (IHC). After resection, morphologic features with additional IHC (CD34 positivity) correctly identified this lesion as a SFT. PAX8 and PAX2 are commonly used as renal tumor markers; however, no series has investigated PAX8 or PAX2 expression in SFT. IHC for PAX8 and PAX2 was performed on 41 SFTs (biopsy and resections) from varying sites. Eight were histologically malignant and eight were recurrences of previous resections. PAX8 staining was observed at least focally in 26.8% (11 of 41) SFT cases; additionally, PAX2 was positive in 12.2% (5 of 41 cases) of SFTs. For PAX8 and PAX2 positive cases 45.6% and 40%, respectively, showed diffuse expression. No correlation was found between PAX8/PAX2 positivity and age, tumor size, site, malignancy, or recurrence. In conclusion, a substantial minority of SFTs express PAX8 and PAX2 via IHC. This presents a diagnostic pitfall when evaluating possible metastases from the kidney, particularly when primary tumors show sarcomatoid or spindle cell morphologies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Biomarkers, Tumor / metabolism
  • Cell Nucleus / metabolism*
  • Female
  • Humans
  • Immunohistochemistry
  • Kidney Neoplasms / metabolism
  • Male
  • Middle Aged
  • Neoplasm Recurrence, Local / metabolism
  • PAX2 Transcription Factor / metabolism*
  • PAX8 Transcription Factor
  • Paired Box Transcription Factors / metabolism*
  • Solitary Fibrous Tumors / metabolism*
  • Transcriptome

Substances

  • Biomarkers, Tumor
  • PAX2 Transcription Factor
  • PAX2 protein, human
  • PAX8 Transcription Factor
  • PAX8 protein, human
  • Paired Box Transcription Factors