Exclusion of Histiocytes/Endothelial Cells and Using Endothelial Cells as Internal Reference Are Crucial for Interpretation of MGMT Immunohistochemistry in Glioblastoma.
ABSTRACT We evaluated the predictive value of O6-methylguanine-DNA methyltransferase (MGMT) protein expression and MGMT promoter methylation status in glioblastomas (GBM) treated with temozolomide (TMZ) in a Taiwan medical center. Protein expression by immunohistochemical analysis (IHC) and MGMT promoter methylation detected by methylation-specific polymerase chain reaction (MSP) were performed in a series of 107 newly diagnosed GBMs. We used endothelial cells as an internal reference for IHC staining because the staining intensities of the MGMT-expressing cells in different specimens varied considerably; a positive result was defined as the staining intensity of the majority of tumor cells similar to that of the adjacent endothelial cells. Immunostainings for microglial/endothelial markers were included as part of the MGMT IHC evaluation, and in cases that were difficult to interpret, double-labeling helped to clarify the nature of reactive cells. The MGMT protein expression was reversely associated with MGMT promoter methylation status in 83.7% of cases (MSP/IHC and MSP/IHC; Pearson r=-0.644, P<0.001). Twenty-two of 24 (91.7%) IHC tumors did not respond to TMZ treatment. Combining MSP and IHC results, all the 15 MSP/IHC GBMs were TMZ resistant. The MGMT status detected by either IHC or MSP was significantly correlated with the TMZ treatment response (both P<0.001) and survival of GBM patients (both P<0.05).
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ABSTRACT: Temozolomide (TMZ) is an oral alkylating agent which is widely used in the treatment of glioblastoma (GBM) and is composed of astrocytic and/or oligodendroglial tumors, and the evaluation of O(6) -methylguanine DNA methyltransferase (MGMT) expression is important to predict the response to TMZ therapy. In this study, we conducted immunohistochemical analysis of 117 cases of Japanese GBM including 19 cases of GBM with oligodendroglioma component (GBMO), using a scoring system for quantitative evaluation of staining intensity and proportion of MGMT, and performed survival analysis of these patients. Immunohistochemically, 55 cases (47%) were positive for MGMT with various intensities and proportions (total score (TS) ≥ 2), while 62 cases (53%) were negative (TS = 0). The distribution of MGMT expression pattern was not affected by any clinicopathological parameters such as the histological subtype (GBM vs. GBMO), age and gender. The survival analysis of these patients revealed that the minimal expression of MGMT (TS ≥ 2) was a significant unfavorable prognostic factor (P < 0.001) as well as resectability (P = 0.004). Moreover, multivariate analysis showed that minimal MGMT expression in GBM was the most potent independent predictor for progression free survival (P < 0.001) and also overall patient survival (P < 0.001). This is the first report employing the scoring system for both staining intensity and proportion to evaluate immunohistochemical MGMT expression in GBM. In addition, our results emphases the clinicopathological values of the immunohistochemical approach for MGMT expression in glioma patients as a routine laboratory examination.Neuropathology 01/2014; 34(3). DOI:10.1111/neup.12091 · 1.80 Impact Factor
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ABSTRACT: O(6)-methylguanine-DNA-methyltransferase (MGMT) is mainly regulated by cytosine-guanine island promoter methylation that is believed to occur only in neoplastic tissue. The present study was undertaken to investigate whether methylation occurs also in non-neoplastic brains by collecting 45 non-neoplastic brains from autopsies and 56 lobectomy specimens from epileptic surgeries. The promoter methylation status of MGMT was studied by methylation-specific polymerase chain reaction (MSP) and pyrosequencing (PSQ), while protein expression was studied by immunohistochemical stain (IHC). The methylation rates, as determined by MSP and PSQ, were 3.0 % (3/101) and 2.9 % (2/69), respectively. Of note, no case had positive result concomitantly from both MSP and PSQ (3 were MSP+/PSQ- and 2 were MSP-/PSQ+), and all the positive samples were further confirmed by cloning and Sanger sequencing. All the methylated cases, except for those having indeterminate IHC results from autopsy specimens, revealed no loss of MGMT protein expression and similar staining pattern to that of the unmethylated cases. In conclusion, the current study demonstrated that MGMT promoter methylation could occur in a low percentage of non-neoplastic brains but did not affect the status of protein expression, which could be regarded as a normal variation in non-neoplastic brains.Journal of Neuro-Oncology 11/2014; 121(3). DOI:10.1007/s11060-014-1663-3 · 2.79 Impact Factor