All procedures were performed according to the manufacturer’s instructions (Imgenex, Corp, San Diego, CA and LifeSpan, BioSciences, Inc.). The antigen-antibody complex was visualized using the Visualization System: Novolink™ Polymer Detection System. Tissue microarray sections were deparaffinized in xylene and rehydrated through graded alcohol concentrations (100%, 96%, 80%, and 70%). For antigen retrieval, slides were pre-treated with a low pH target retrieval solution (Dako). Endogenous biotin was blocked with an appropriate kit. Sections were incubated for 1 hour with an antibody against the human MGMT (monoclonal antibody; clone MT3.1; dilution: 1:50, Imgenex, Corp, San Diego, CA and monoclonal antibody from LifeSpan, BioSciences, Inc., dilution 1:50). Only a nuclear staining was considered positive. Tonsil tissue served as a positive control. The immunoreactivity was scored semi-quantitatively as follows: 0:<5% positive tumor cells, 1+: 5-75% positive tumor cells, 2+: 75-95% positive tumor cells, 3+: >95% positive tumor cells (29 (link)); data were subsequently combined into a MGMT-negative (<5% positive) and MGMT-positive (>5% positive) categories (Supplemental Table 1). The testing lab was blinded to patient characteristics.