Poster Presentation 28th Lorne Cancer Conference 2016

Diagnostic use of array-Comparative Genomic Hybridisation (aCGH) to distinguish melanocytic naevi and melanoma in paraffin embedded tissue (#236)

Cleo Robinson 1 2 3 , Nima Mesbah Ardakani 1 2 , Benjamin A Wood 1 2 , Nathan T Harvey 1 2 , Carla Thomas 1 2 , Benhur Amanuel 1 2
  1. Anatomical Pathology, PathWest, Perth, WA, Australia
  2. School of Pathology and Laboratory Medicine, University of Western Australia, Perth, WA, Australia
  3. School of Medicine and Pharmacology, University of Western Australia, Perth, WA, Australia

Introduction: Distinction between melanocytic naevi and melanoma poses a diagnostic challenge in ambiguous cases showing overlapping histological features. As incidence of melanoma continues to rise, this is a growing concern, particularly as early diagnosis has a major impact on survival. Melanomas are characterised by the presence of multiple genomic copy number variations (CNVs), while this is not a feature of melanocytic naevi.  Array-based comparative genomic hybridisation (aCGH) can detect CNVs and contribute to the diagnosis in histologically ambiguous cases. We assessed the feasibility and utility of aCGH to assess CNV in melanocytic lesions.

Methods: DNA was extracted from formalin fixed paraffin embedded (FFPE) sections of unambiguous naevi (n=18) and melanomas (n=22), after careful microdissection. The test DNA and gender mismatched human reference DNA were differentially labelled with fluorophores (Agilent).  Equal quantities of the two DNA samples were mixed and co-hybridised to a SurePrint G3 Human CGH 8x60K array (Agilent).Digital scanning was used to capture and quantify the relative fluorescence intensities. The ratio of the fluorescence intensities was analysed by Cytogenomics software (Agilent).   

Results: Frequent large CNVs were identified in the melanoma samples, including whole chromosomal gains and losses and smaller focal aberrations, consistent with previously reported findings.  None of the benign naevi had large copy number changes. Overall aCGH quality was good, with unsatisfactory results due to low signal intensity in only three cases. Copy number changes were confirmed by FISH in 3 cases and single nucleotide (SNP) array in 2 cases.

Conclusions: This technique can successfully be used to analyse diagnostic FFPE samples with a high specificity (100%) and sensitivity (100%). Cost per sample and assay turn-around time were considered suitable for routine testing provided samples were batched (6-8 samples). Further investigation of histologically ambiguous samples, particularly spitzoid neoplasms, is the next step to confirm the success of this approach.