Diagnostic Accuracy of Immunohistochemistry in Detecting MGMT Methylation Status in Patients with Glioma

Abstract

Background: The O6-methylguanine-DNA methyltransferase (MGMT) gene prevents mismatch in DNA replication and transcription by repairing mutagenic DNA lesions. MGMT is a predictor biomarker of chemotherapy in high-grade and low-grade gliomas based on high-risk clinical conditions. It also can be used for therapeutic decisions to predict hypermutation in recurrence in newly diagnosed low-grade gliomas. The gold standard examination for the methylation is Polymerase Chain Reaction (PCR). However, this technique is not widely available in Indonesia for daily practice. Thus, an uncomplicated and simpler method such as immunohistochemistry (IHC) is needed as an alternative examination. This study aimed to predict the diagnostic accuracy of immunohistochemistry (IHC) in detecting the methylation status of O6-methylguanine-DNA methyltransferase (MGMT) in glioma.

Methods: This research was a cross-sectional study using formalin-fixed paraffin embedded (FFPE) tissue samples of glioma patients, dating between October 2017 until March 2021. Diagnosis of glioma was established based on clinical, radiological, and histopathological findings. MGMT methylation status was investigated using the IHC and PCR techniques. Diagnostic value of IHC was analyzed, with PCR as a gold standard method. Optimum threshold to determine positivity of IHC was determined by the Area Under the Curve (AUC) on Receiver Operating Characteristics (ROC) curve and Youden index.

Results: Among 75 samples examined, 29 (38.7%) patients were methylated. IHC detected MGMT methylation with sensitivity of 86.2%, specificity of 63.0%, positive predictive value of 59.5%, negative predictive value of 87.9% and accuracy of 72.0%. The AUC was 0.746, indicating moderate diagnostic value. Optimum positivity threshold of the IHC examination based on Youden Index was 10%.

Conclusion: IHC examination can be used to detect MGMT methylation status of glioma patients in limited resources setting, where PCR technique is not available.

Keywords: Diagnostic accuracy; Glioma; IHC; PCR; methylated MGMT.

Figure 1

Immunohistochemical Results of MGMT Methylation (magnification 400x). (A). Unmethylated status was determined by a positive nuclear staining of the tumor using anti-MGMT antibody (MT3.1) ab39253 which was assessed quantitatively using eye balling technique with a cut-off of ≥10%. (B). Methylated status was determined by a negative nuclear staining with cut-off <10%.

Figure 2

Methylation-specific PCR Curve Shows the Amplification of MGMT with COL2A1 as internal control (red), methylated MGMT gene promoter (green) and unmethylated MGMT gene promoter (blue); (A) Methylated status is marked with green curve under red curve; (B) Unmethylated is interpreted if blue curve under red curve

Figure 3

AUC Value was 0.746, Indicating Moderate Diagnostic Value on the ROC Curve