Elevated PDGFRB gene copy number gain as prognostic in resected malignant pleural mesothelioma.

Abstract

7078 Background: PDGF/PDGFR pathway has been implicated in malignant pleural mesothelioma (MPM) carcinogenesis. We sought to evaluate the incidence of PDGFRB gene copy number gain (CNG) and PDGFR pathway protein expression by immunohistochemistry (IHC) in the tumor cell cytoplasm, membrane, nucleus, and stroma, and correlate it to patient clinical outcome. Methods: 88 archived tumor blocks from resected MPM with full clinical information were used to perform the analyses. IHC biomarkers for PDGFRα,β and p-PDGFRβ, and fluorescence in situ hybridization were performed for analysis of PDGFRB gene CNG. Spearman’s rank correlation, Wilcoxon rank-sum test or Kruskal-Wallis test, BLiP plots, and Kaplan-Meier method were used to assess the biomarkers and their correlation to clinical outcome. Results: There were several correlations identified between the IHC biomarkers; however, none associated with patient demographics or histology subtype, with the exception of high cytoplasmic PDGFRα occurring in patients with no prior known asbestos exposure (p=0.029). In the CNG analysis, PDGFRB gene CNG in > 10% of tumor cells had lower cytoplasmic p-PDGFRβ (p=0.029), while PDGFRB gene CNG in > 40% of tumor cells had a higher cytoplasmic PDGFRβ (p=0.04). PDGFRB gene CNG status did not associate with patient demographics or tumor characteristics. Patients with PDGFRB CNG > 40% of tumor cells had an improved relapse-free survival (RFS) [HR 0.25 (95% CI 0.09, 0.72), p=0.0096]. In the patients with PDGFRB CNG > 40% of cells, the addition of chemotherapy appeared to also improve RFS (p=0.017). In the multi-covariate analyses for RFS, there was no association with any IHC biomarker. In the overall survival (OS) analysis, having PDGFRB gene CNG > 40% of tumor cells correlated with an improved OS [HR 0.32 (95% CI 0.11, 0.89), p=0.029] and the addition of peri-operative chemotherapy led to a trend towards improved OS (p=0.089). Conclusions: PDGFRB CNG > 40% of tumor cells is a potential prognostic biomarker in surgically resected MPM tumors. Adding chemotherapy to patients with PDGFRB CNG > 40% of cells improved RFS and led to a trend towards improved OS. Future validation of this biomarker in prospective trials is needed.