MGMT promoter methylation status and DNA mismatch repair genes in paired primary and recurrent glioblastoma: A translational study of the German Glioma Network.

Abstract

2076 Background: Hypermethylation of the MGMT promoter is strongly associated with longer progression-free and overall survival in glioblastoma patients. We here addressed the question whether glioblastoma relapses are associated with changes in the MGMT promoter methylation status or altered expression of the DNA mismatch repair genes, MLH1, MSH2, MSH6 and PMS2. Methods: MGMT promoter methylation status was analysed in paired primary and recurrent glioblastoma samples containing vital tumor of 80 patients using non-quantitative methylation-specific PCR (MSP). Quantitative promoter methylation analyses using DNA pyrosequencing were performed, too, for MGMT in 48 patients as well as for the DNA mismatch repair genes MLH1, MSH2, MSH6 and PMS2 in 42 patients. Furthermore, levels of MGMT, MLH1, MSH2, MSH6 and PMS2 proteins were analysed semiquantitatively by immunohistochemistry in 42 patients. Results: MSP revealed MGMT promoter hypermethylation in 28 patients, borderline methylation in 3 patients and no methylation in 49 patients at diagnosis. In 71 of the 80 patients, the MGMT promoter status was retained at recurrence. In 7 patients, loss or reduction of MGMT promoter methylation was detected in the recurrent tumor, in 3 patients this finding was explained by low tumor cell contents in the recurrent tumor specimen. Two patients showed a change from unmethylated to borderline methylation and borderline methylation to hypermethylation, respectively. None of the investigated primary and recurrent glioblastomas showed MLH1, MSH2, MSH6 or PMS2 promoter hypermethylation. Immunohistochemical expression scores for MLH1, MSH2, MSH6 and PMS2 proteins were frequently reduced in the recurrent as compared with the corresponding primary tumor. Conclusions: The MGMT promoter methylation status does not change from the primary to the recurrent tumor in the vast majority of glioblastoma patients. Our results further suggest that glioblastoma recurrences often demonstrate lower MLH1, MSH2, MSH6 and/or PMS2 immunoreactivity scores. However, MLH1, MSH2, MSH6 and PMS2 promoter hypermethylation does not appear to be involved in glioblastoma recurrence. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Essex Pharma, Merck Serono, Roche