title: 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).
authors.affiliation: Department of Pathology and Laboratory Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Chih-Yi
authors.initials: CY
authors.lastname: Hsu
authors.forename: Shih-Chieh
authors.initials: SC
authors.lastname: Lin
authors.forename: Hsiang-Ling
authors.initials: HL
authors.lastname: Ho
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Chang-Chien
authors.forename: Sanford P-C
authors.initials: SP
authors.lastname: Hsu
authors.forename: Yu-Shu
authors.initials: YS
authors.lastname: Yen
authors.forename: Ming-Hsiung
authors.initials: MH
authors.lastname: Chen
authors.forename: Wan-You
authors.initials: WY
authors.lastname: Guo
authors.forename: Donald M-T
authors.initials: DM
authors.lastname: Ho
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000378:metabolism; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000188:drug therapy / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000627:therapeutic use; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D005260:Female; D005909:Glioblastoma / Q000175:diagnosis* / Q000188:drug therapy / Q000378:metabolism; D006644:Histiocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011401:Promoter Regions, Genetic; D013194:Staining and Labeling / Q000379:methods; D015996:Survival Rate; D013624:Taiwan / Q000453:epidemiology; D000077204:Temozolomide; D016896:Treatment Outcome; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D055815:Young Adult
chemical_list: D018906:Antineoplastic Agents, Alkylating; D014408:Biomarkers, Tumor; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide