Department of Neurology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California, USA.
Neuro Oncol. 2013 Mar;15(3):370-81. doi: 10.1093/neuonc/nos308. Epub 2013 Jan 17.
Promoter methylation of the DNA repair gene, O-6-methylguanine-DNA methyltransferase (MGMT), is associated with improved treatment outcome for newly diagnosed glioblastoma (GBM) treated with standard chemoradiation. To determine the prognostic significance of MGMT protein expression as assessed by immunohistochemistry (IHC) and its relationship with methylation, we analyzed MGMT expression and promoter methylation with survival in a retrospective patient cohort.
We identified 418 patients with newly diagnosed GBM at University of California Los Angeles Kaiser Permanente Los Angeles, nearly all of whom received chemoradiation, and determined MGMT expression by IHC, and MGMT promoter methylation by methylation-specific PCR (MSP) and bisulfite sequencing (BiSEQ) of 24 neighboring CpG sites.
With use of the median percentage of cells staining by IHC as the threshold, patients with <30% staining had progression-free survival (PFS) of 10.9 months and overall survival (OS) of 20.5 months, compared with PFS of 7.8 months (P < .0001) and OS of 16.7 months (P < .0001) among patients with ≥30% staining. Inter- and intrareader correlation of IHC staining was high. Promoter methylation status by MSP was correlated with IHC staining. However, low IHC staining was frequently observed in the absence of promoter methylation. Increased methylation density determined by BiSEQ correlated with both decreased IHC staining and increased survival, providing a practical semiquantitative alternative to MSP. On the basis of multivariate analysis validated by bootstrap analysis, patients with tandem promoter methylation and low expression demonstrated improved OS and PFS, compared with the other combinations.
Optimal assessment of MGMT status as a prognostic biomarker for patients with newly diagnosed GBM treated with chemoradiation requires determination of both promoter methylation and IHC protein expression.
DNA 修复基因 O-6-甲基鸟嘌呤-DNA 甲基转移酶（MGMT）的启动子甲基化与新诊断的胶质母细胞瘤（GBM）患者接受标准放化疗治疗后的治疗结果改善相关。为了确定免疫组织化学（IHC）评估的 MGMT 蛋白表达的预后意义及其与甲基化的关系，我们分析了加利福尼亚大学洛杉矶分校 Kaiser Permanente Los Angeles 的一个回顾性患者队列中的 MGMT 表达和启动子甲基化与生存的关系。
我们确定了加利福尼亚大学洛杉矶分校 Kaiser Permanente Los Angeles 新诊断为 GBM 的 418 名患者，他们几乎都接受了放化疗，并通过 IHC 确定了 MGMT 表达，通过甲基化特异性 PCR（MSP）和 24 个相邻 CpG 位点的亚硫酸氢盐测序（BiSEQ）确定了 MGMT 启动子甲基化。
使用 IHC 染色的细胞百分比中位数作为阈值，<30%染色的患者无进展生存期（PFS）为 10.9 个月，总生存期（OS）为 20.5 个月，而≥30%染色的患者 PFS 为 7.8 个月（P<0.0001）和 OS 为 16.7 个月（P<0.0001）。IHC 染色的读者间和读者内相关性较高。MSP 确定的启动子甲基化状态与 IHC 染色相关。然而，在缺乏启动子甲基化的情况下，经常观察到低 IHC 染色。通过 BiSEQ 确定的增加的甲基化密度与降低的 IHC 染色和增加的生存相关，为 MSP 提供了一种实用的半定量替代方法。基于通过 bootstrap 分析验证的多变量分析，与其他组合相比，串联启动子甲基化和低表达的患者表现出更好的 OS 和 PFS。
为接受放化疗治疗的新诊断 GBM 患者进行 MGMT 状态作为预后生物标志物的最佳评估需要确定启动子甲基化和 IHC 蛋白表达。
