Abstract
PURPOSE: There remain a lack of biomarkers for endocrine therapy resistance in patients with breast cancer (BC), which is proving to be a great challenge. In vitro experiments have shown that downregulation of PTEN expression leads to resistance to tamoxifen (TAM) in BC cells. We aimed to investigate the predictive role of tumor PTEN promoter methylation and PTEN expression in long-term survival after TAM adjuvant therapy in patients with early-stage BC. METHODS: From 2001 to 2013, 105 patients with stage I-III BC who were treated with standardized adjuvant TAM for 5 years or until relapse in West China Hospital (WCH) were enrolled in this study. PTEN expression and DNA methylation of three specified sequences from the PTEN promoter in primary tumors were measured using immunohistochemistry and pyrosequencing. A cohort of 159 hormone receptor-positive patients receiving TAM treatment from The Cancer Genome Atlas (TCGA) database was used for verification. RESULTS: Median follow-up time for the WCH cohort was 141.7 months. The low, moderate, and high PTEN expression groups had differing 10-year disease-free survival (DFS) (42.3%, 55%, 81%, respectively, P = 0.027) and overall survival (OS) rates (65%, 84.2%, 90.5%, respectively, P = 0.027). Higher methylation levels of the second sequence (- 819 to - 787 bp), rather than the first (- 1143 to - 1107 bp) or third sequence (- 663 to - 593 bp), independently increased the risk of disease recurrence (hazard ratio = 2.60) and death (hazard ratio = 3.79) in the WCH cohort, according to multivariate Cox regression analysis. Importantly, out of the five CpG islands located within this sequence, only high methylation of the - 796 CpG island predicted shorter DFS and OS. In TCGA validation cohort, there was also a trend of higher methylation of the - 796 CpG island correlating with shorter disease-free intervals, with borderline significance (P = 0.057). CONCLUSION: Low PTEN expression and high methylation of its promoter (sequence - 819 to - 787 bp) in tissue predict poor DFS and OS in hormone receptor-positive early BC patients who received adjuvant TAM.