The unique molecular signatures of nodular and superficial spreading melanoma

Abstract

9047 Background: Primary nodular melanoma (NM) patients have a relatively poor prognosis compared to superficial spreading melanoma (SSM) patients. The disparity is generally attributed solely to NM's advanced thickness at presentation. In this study we attempted to define molecular signatures of NM and SSM that may explain their clinical differences. Methods: We performed an in silico gene expression analysis of 2 public data sets consisting of 36NM and 54 SSM primary melanoma tissues (CCR 2007;13 and JNCI 2006;98). We then utilized DNA microarray to generate gene expression profiles of a panel of 22 melanoma cell lines (2SSM, 4 NM, 12 met, 4 melanocytes). Differentially expressed genes and over-represented pathways in NM and SSM were identified based on a pooled analysis of the 3 data sets. We then used SNP array to define genomic alterations unique to NM and SSM but not altered in normal melanocytes. Finally, we correlated SNP array with gene expression. Results: Genes significantly overexpressed (p<0.05) in NM showed over-representation of pathways related to MAPK signaling (p=0.05) and cytoskeleton organization (p=0.02), while SSM showed over-representation of cell communication (p=0.05) and primary metabolic processes (p=0.002). Notable correlations between gene expression and copy number alteration in NM include increased copy number/overexpression of SOX5 (transcription factor related to embryonic development and cell fate) and the downregulation/deletion of ST14 (suppression of tumorigenicity 14). SSM demonstrated concordance of increased copy number/overexpression of EZR (cell adhesion protein implicated in human cancer) as well as PALLD (a protein related to motility, adhesion, and extracellular matrix interactions). Notable SSM genes showing correlation between downregulation/deletion include BNIP3 (a pro-apoptotic protein) and MTAP (often co- deleted with tumor suppressor p16). Conclusions: Simultaneous integration of gene expression with SNP array revealed molecular signatures characteristic of NM and SSM. These results suggest that NM and SSM are distinct biologic entities and that molecularly targeted adjuvant therapy may be more effective if tailored to the molecular signatures of melanoma subtypes. Validation is necessary to draw further conclusions. No significant financial relationships to disclose.