DNA methylation profile predicts survival of patients with resected malignant pleural mesothelioma (MPM)

Abstract

7712 Background: Methylation in different tumor suppressor genes is among the most frequent alterations reported in MPM patients (pts). DNA methylation increases upon immortalization and transformation of human mesothelial cells, and demethylating agents were found to have some activity in MPM. In this study we analysed the methylation status of the promoter region of four candidate genes in MPM: p15INK4BINK4B, p16INK4AINK4A, RASSF1A and NORE1A. Methods: Samples of 79 consecutive MPM pts who underwent surgical procedures (41 extrapleural pneumonectomy (EPP), 32 partial pleurectomy, 6 diagnostic biopsy) at our Institution from 1997 to 2005 were analyzed. DNA was isolated from each paraffin-embedded MPM; the methylation status of the four genes was evaluated by a methylation-specific PCR method (MSP). Correlations between methylation status, clinico-pathological parameters (including proliferation index) and overall survival (OS) were examined in all pts and in the EPP subgroup. Proliferation index was evaluated as percentage of nuclear immunoreactivity/10 high-power field using a mouse monoclonal antibody anti-human Ki-67, clone MIB-1 (DAKO Corporation, Carpinteria, CA). Results: The MSP analysis documented gene promoter methylation in at least one gene in 30 cases (38%). The methylation frequency of each gene was: p15INK4B 15 cases (19%), p16INK4A 9 (11.4%), RASSF1A 16 (20.2%), Nore1A 4 (5.1%). Of the 30 methylated MPMs, 18 (60%) showed only one methylated gene, 10 (33.3%) were methylated in two genes and 2 (6.7%) in three. Methylation in at least one gene was associated to a higher proliferation index (P=0.058, ANOVA), but not to OS, in the whole study population. In pts treated with EPP, the 22 methylated cases showed a trend to a worst OS in comparison to 19 unmethylated cases (median OS 16 months vs 35 months, P=0.066, HR=2.01, 95% CI 0.94–4.30, Cox regression), independently by histology and nodal status. Conclusions: In pts treated with EPP, the methylation profile of p15INK4BINK4B, p16INK4AINK4A, RASSF1A and NORE1A appeared to be an independent prognostic factor for OS. The methylation status was correlated to proliferation rate, indicating a potential role of these oncosuppressor genes in the neoplastic progression of MPM. No significant financial relationships to disclose.