Immunohistochemical evaluation of O 6 ‐methylguanine DNA methyltransferase ( MGMT ) expression in 117 cases of glioblastoma

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