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

Abstract

Background: 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.

Objective: 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.

Results: 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.

Conclusions: 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.

Keywords: Array CGH; Chromosome 18; MALT1; Outcome; Prostate cancer.

Fig. 1.

Primary prostate tissues were obtained from the University of Texas Health Science Center Genitourinary Tissue Bank. A minimum of 5-year clinical follow up data was collected for each patient with non-progressing disease. Primary tumor tissues were characterized on outcome as No evidence of disease (NED) or confirmed Metastasis (MET) following prostatectomy. Final analysis including a total of 17 METs and 17 NEDs.

Fig. 2.

Two significant copy number gains on 18q associated with patient outcome were identified by arrayCGH. (A) In NED outcome tumors (5 of 17 samples) copy number gain at chromosomal location 18q11.2 was statistically associated with good outcome as analyzed via the Default Analysis Method-CGH v2 Agilent Cytogenomic software. (B) In MET outcome tumors (6 of 17 samples), copy number gain at 18q21.32 was statistically associated with poor outcome.

Fig. 3.

Immunohistochemical quantification of protein expression of MALT1, ALPK2, and NEDD4L genes located within the gain at 18q21.31. (A) Tumor tissue from MET outcome patients that showed no copy number gain at 18q21.31 show positive stain for MALT1, ALPK2, and NEDD4L. (B) Tumor tissue from patients with the gain show increased staining of MALT1 and NEDD4L, while ALPK2 shows no clear increase in stain. (C) Average H-scores based on intensity of the staining of cancerous glands indicate higher expression of both MALT1 and NEDD4L in samples that contain the chromosomal gain, while ALPK2 shows the decreased expression.