Immunohistochemistry for O⁶-methylguanin-DNA methyltransferase in glioblastomas defined by WHO2016: Correlation with promoter methylation status and patients’ progression-free survival with the cut-off value determined by ROC analysis

Although promoter methylation status is known to correlate with response to alkylating agents, immunohistochemistry (IHC) is the only available method for MGMT status in many institutions. However, the clinical utility of MGMT IHC is controversial. A hundred and twenty four cases of primary glioblastoma diagnosed by morphology-based criteria over 2 decades were re-appraised based on WHO 2016 classification. Tumor MGMT status was evaluated by IHC and methylation-specific PCR (MSP) to see if any correlation between the results of the 2 methods. The association with patients’ prognoses was also investigated. Among 124 cases, 116 were confirmed to be glioblastoma by definition of WHO2016, and median overall survival (OS) of glioblastoma, IDH-wildtype and epithelioid glioblastoma were 18 and 27 months, respectively. MGMT promoter methylation status significantly correlated with progression-free survival (PFS) (p = 0.014) but not with OS (p = 0.364) in patients with glioblastoma by the integrated diagnosis. With the cut-off value of 24.5% of positive cell ratio as determined by receiver operating characteristic (ROC) analysis, there was a good correlation between the results of IHC and MSP (p = 0.08 × 10⁻²⁴). Accordingly, there was a marginal association between the results of IHC and patients’ PFS (p = 0.063), but not OS (p = 0.563). When the patients were divided into pre and post temozolomide era, the association of MGMT promoter methylation status with PFS was only noted in the patients of temozolomide era (pre, p = 0.432; post, p = 0.015).