Differential genomic profiles of tumor-involved and tumor-free sentinel lymph nodes in patients with melanoma.

Abstract

9043 Background: For clinical stage I and II node negative melanoma the histologic status of the sentinel lymph node (SLN) is the most significant predictor of survival. Molecular characterization of node positive and node negative SLNs through gene expression profiling may improve the understanding of the molecular mechanisms of metastasis and identify specific gene signatures for SLN+/SLN- that correlate with clinical outcome. Methods: We characterized 15 SLN+ and 15 SLN- melanoma patients (T3a/b, T4a/b) who underwent SLN dissection for routine staging using transcriptome profiling analysis on 5μ sections of fresh LN samples. The primary endpoint was mRNA expression profiling using the U133A 2.0 Affymetrix gene chips. Significance Analysis of Microarrays v.4 was used to perform non-parametric analysis and statistical comparison for each transcript corrected for false discovery rate (q value) to control for type 1 errors arising from multiple tests. Pathway analysis was performed using Ingenuity Pathway Analysis software. Results: Tumor size ranged from 1-2mm in size. Twenty-one genes were expressed at significantly (q value <0.056) higher levels in SLN+ vs SLN-. These included CCNA2, CEP55, DCT, FEN1, HMMR, MLANA, PAICS, PBK, POSTN, RAB27A, RRM2, SHCBP1, SILV, TYR, CENPE, CCL20, CHEK1, LINS, TPX2, TTK, TYRP1. Pathway analysis (39 genes >1.4 fold; q < 0.12) identified the top disease categories as “Cancer” (26 genes, p = 5.7x10-9) and “Dermatological” (14 genes, p = 3.9x10-6). The top functional categories included “Cell Cycle” (21 genes p= 2.3x10-12) and “Cell Growth and Proliferation” (26 genes p=9x10-9). The relevant canonical pathways were “Eumelanin Biosynthesis” (p=3x10-5) and “Cell Cycle: G2/M DNA Damage Checkpoint Regulation” (p=1.2x10-4). Conclusions: We identified a 21 gene signature that is consistent with metastatic melanoma and its microenvironment and is differentially expressed in SLNs that are tumor involved. These gene families provide a signature of nodal involvement that may assist in diagnosis, and may be further explored towards prediction of outcome and development of therapy. A validation study is ongoing with clinical outcome association analyses as follow up is mature.