title: A subset of solitary fibrous tumors express nuclear PAX8 and PAX2: a potential diagnostic pitfall.
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.
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: McDaniel
authors.affiliation: Michigan Center for Translational Pathology and Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Nallasivam
authors.initials: N
authors.lastname: Palanisamy
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Smith
authors.affiliation: Michigan Center for Translational Pathology and Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Dan R
authors.initials: DR
authors.lastname: Robinson
authors.affiliation: Michigan Center for Translational Pathology and Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Yi-Mi
authors.initials: YM
authors.lastname: Wu
authors.affiliation: Michigan Center for Translational Pathology, Department of Pathology, Department of Urology, Comprehensive Cancer Center and Howard Hughes Medical Institute, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Arul M
authors.initials: AM
authors.lastname: Chinnaiyan
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: McHugh
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Joel K
authors.initials: JK
authors.lastname: Greenson
authors.affiliation: Michigan Center for Translational Pathology, Department of Pathology and Comprehensive Cancer Center, University of Michigan Medical School, Ann Arbor, MI, USA. lkunju@med.umich.edu.
authors.forename: Lakshmi P
authors.initials: LP
authors.lastname: Kunju
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000378:metabolism; D051762:PAX2 Transcription Factor / Q000378:metabolism*; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000378:metabolism*; D054364:Solitary Fibrous Tumors / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D014408:Biomarkers, Tumor; D051762:PAX2 Transcription Factor; C497318:PAX2 protein, human; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors