A copy number gain on 18q present in primary prostate tumors is associated with metastatic outcome

Most prostate cancers (CaPs) grow slowly and remain indolent, yet some become aggressive and metastasize. Clinical decision-making requires prognostic markers that can be utilized at the time of diagnosis to identify aggressive tumors. Previous studies have shown a correlation between genomic alterations on the long arm of chromosome 18 (18q) and metastatic CaP.

The goal of this study was to comprehensively profile copy number alterations found on 18q in prostate tumors with varying outcomes to identify putative biomarkers associated with more aggressive disease METHODS: A custom comparative genomic hybridization array was created composed of high-density tiling of 18q sequences. Primary prostate tumor tissues were gathered from men who underwent radical prostatectomy and were categorized based on the patient's long-term clinical outcome as either metastatic disease (MET) or no evidence of disease (NED). DNA was isolated from formalin-fixed, paraffin-embedded prostatectomy tumor tissues, and analyzed for copy number variations (CNVs). Protein levels of genes found within the region of CNVs were analyzed using immunohistochemistry.

Thirty-Four primary prostate tumors were analyzed: 17 NEDs and 17 METs. Two significant regions of copy number gains were found on 18q associated with outcome. One gain located at 18q11.2 was found exclusively in NED outcome tumors while another gain, located at 18q21.31, was found exclusively in MET outcome tumors (P -value< 0.0076). Immunohistochemistry analysis of protein levels showed more protein associated with copy number gain in the MET samples vs. those without the gain as indicated by H-scores of 184.7 and 121.0 respectively.

The latter of these CNVs represent a putative biomarker for aggressive disease and highlights a putative metastasis promoting gene. Further study of known connections to CaP suggests that the paracaspase MALT1 is the most likely target of the copy number gain and represents a potential therapeutic target. Future studies would be of interest to determine MALT1's role in aggressive CaP and the ability of this CNV region to differentiate CaP that will eventually metastasize.