title: Will PAXgene substitute formalin? A morphological and molecular comparative study using a new fixative system.
abstract: Formalin fixation and paraffin embedding present the standard procedures for conserving clinical tissues for histological analysis. However, molecular analysis is impaired by the cross linking properties of formalin. The PAXgene tissue system (PreAnalytix, Switzerland) is a new formalin-free tissue collection device.
  
  
  OBJECTIVE
  In this study we aimed to evaluate this new tissue preservation technique in comparison with formalin fixation and fresh frozen tissue samples.
  
  
  METHODS
  12 melanoma biopsy samples were divided and fixed simultaneously with formalin, PAXgene or fresh frozen in liquid nitrogen and analysed with regard to morphology, immunohistochemistry,  DNA and RNA content and quality. Markers of melanocytic differentiation and tumour cell proliferation were used.
  
  
  RESULTS
  Morphology was well preserved in PAXPE samples. However, 5 out of 11 immunohistochemical markers showed significantly lower overall staining and staining intensity with PAXPE tissues in comparison with formalin-fixed, paraffin-embedded (FFPE). Increasing membrane permeability through adding a detergent did proportionally increase staining intensity in PAXPE samples. Amplification of different mRNA amplicons showed a direct relationship with the size of the amplicon with greater template integrity observed in PAXPE samples. Sequencing and mutational analysis of DNA samples were comparable for all the different fixation methods, while the level of DNA fragmentation seemed to be lower in PAXPE compared with FFPE tissues.
  
  
  CONCLUSIONS
  The switch from formalin to PAXgene fixation would require a re-evaluation of immunohistochemical markers and staining procedures originally developed for FFPE tissues. Our data demonstrate that PAXPE fixation offers some advantages concerning molecular analysis. However, these advantages would not justify substituting formalin fixation in any routine pathology laboratory.
authors.affiliation: Department of Dermatology, University Hospital of Zurich, Zurich, Switzerland.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Belloni
authors.forename: Chiara
authors.initials: C
authors.lastname: Lambertini
authors.forename: Paolo
authors.initials: P
authors.lastname: Nuciforo
authors.forename: Jay
authors.initials: J
authors.lastname: Phillips
authors.forename: Eric
authors.initials: E
authors.lastname: Bruening
authors.forename: Stephane
authors.initials: S
authors.lastname: Wong
authors.forename: Reinhard
authors.initials: R
authors.lastname: Dummer
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics; D001706:Biopsy; D004247:DNA / Q000032:analysis; D053938:DNA Fragmentation; D004252:DNA Mutational Analysis; D004867:Equipment Design; D005260:Female; D005404:Fixatives; D005557:Formaldehyde; D005615:Freezing; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008545:Melanoma / Q000737:chemistry / Q000235:genetics / Q000473:pathology*; D008875:Middle Aged; D016612:Paraffin Embedding; D011237:Predictive Value of Tests; D055550:Protein Stability; D020871:RNA Stability; D012333:RNA, Messenger / Q000032:analysis; D060888:Real-Time Polymerase Chain Reaction; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012878:Skin Neoplasms / Q000737:chemistry / Q000235:genetics / Q000473:pathology*; D013194:Staining and Labeling; D016707:Tissue Fixation / Q000295:instrumentation / Q000379:methods*
chemical_list: D014408:Biomarkers, Tumor; D005404:Fixatives; D012333:RNA, Messenger; D005557:Formaldehyde; D004247:DNA