Influence of MMR, MGMT Promotor Methylation and Protein Expression on Overall and Progression-Free Survival in Primary Glioblastoma Patients Treated with Temozolomide

Abstract

Glioblastoma is the most common malignant brain tumor in adults. Standard treatment includes tumor resection, radio-chemotherapy and adjuvant chemotherapy with temozolomide (TMZ). TMZ methylates DNA, whereas O6-methylguanine DNA methyltransferase (MGMT) counteracts TMZ effects by removing the intended proteasomal degradation signal. Non-functional MGMT mediates the mismatch repair (MMR) system, leading to apoptosis after futile repair attempts. This study investigated the associations between MGMT promoter methylation, MGMT and MMR protein expression, and their effect on overall survival (OS) and progression-free survival (PFS) in patients with glioblastoma. MGMT promoter methylation was assessed in 42 treatment-naïve patients with glioblastoma WHO grade IV by pyrosequencing. MGMT and MMR protein expression was analyzed using immunohistochemistry. MGMT promoter methylation was present in 52%, whereas patients <70 years of age revealed a significantly longer OS using a log-rank test and a significance threshold of p ≤ 0.05. MGMT protein expression and methylation status showed no correlation. MMR protein expression was present in all patients independent of MGMT status and did not influence OS and PFS. Overall, MGMT promoter methylation implicates an improved OS in patients with glioblastoma aged <70 years. In the elderly, the extent of surgery has an impact on OS rather than the MGMT promoter methylation or protein expression.

Keywords: MGMT promoter methylation; MGMT protein expression; glioblastoma; immunohistochemical analysis; mismatch repair; temozolomide.

Figure 1

Kaplan–Meier estimates of overall survival (OS) in patients with glioblastoma WHO grade IV. (A) OS of patients stratified by age at diagnosis younger than 70 years and older than 70 years. (B) OS of patients stratified by MGMT promoter methylation status. (C) OS in patients younger than 70 years, comparing MGMT promoter methylation. (D) OS in patients older than 70 years, comparing MGMT promoter methylation. The hazard ratio (HR) and the 95% confidence interval in are stated in brackets. Statistical significance between the groups was evaluated using a log-rank test.

Figure 2

Representative images of the hematoxylin/eosin (HE) staining and the immunohistochemical staining for MGMT protein. Case 1 represents MGMT^met+/MGMT^high, case 2 MGMT^met−/MGMT^high, case 3 MGMT^met+/MGMT^low and case 4 MGMT^met−/MGMT^low. Images were taken using the Pannoramic Scan software v1.15.0.57 of a 3D Histech Scanner, and exemplary areas were determined via the Panoramic Viewer software v2.4.0.53492. Arrow heads indicate MGMT-positive cells. V = vessel; scale bar = 100 µm; insert scale bar = 20 µm.

Figure 3

Representative images of the hematoxylin/eosin (HE) staining and the immunohistochemical staining for the mismatch repair system (MMR). All four cases show a positive MMR signal. Case 1 represents MGMT^met+/MMGT^high, case 2 MGMT^met−/MGMT^high, case 3 MGMT^met+/MGMT^low and case 4 MGMT^met−/MGMT^low. Brownish color indicates a positive MMR staining with diaminobenzidine. Images were taken using a 3D Histech Scanner, and exemplary areas were determined via the Panoramic Viewer software. Scale bar = 100 µm.