MGMT-STP27 methylation status as predictive marker for response to PCV in anaplastic oligodendrogliomas and oligoastrocytomas. A report from EORTC study 26951

Purpose: The long-term follow-up results from the EORTC-26951 trial showed that the addition of procarbazine, CCNU, and vincristine (PCV) after radiotherapy increases survival in anaplastic oligodendrogliomas/ oligoastrocytomas (AOD/AOA). However, some patients appeared to benefit more from PCV treatment than others. Experimental Design:Weconducted genome-wide methylation profiling of 115 samples included in the EORTC-26951 trial and extracted theCpGisland hypermethylated phenotype (CIMP) andMGMTpromoter methylation (MGMT-STP27) status. Results: We first show that methylation profiling can be conducted on archival tissues with a performance that is similar to snap-frozen tissue samples. We then conducted methylation profiling on EORTC-26951 clinical trial samples. Univariate analysis indicated that CIMP? or MGMT-STP27 methylated tumors had an improved survival compared with CIMP- and/or MGMT-STP27 unmethylated tumors [median overall survival (OS), 1.05 vs. 6.46 years and 1.06 vs. 3.8 years, both P < 0.0001 for CIMP and MGMT-STP27 status, respectively]. Multivariable analysis indicates that CIMP and MGMT-STP27 are significant prognostic factors for survival in presence of age, sex, performance score, and reviewdiagnosis in themodel. CIMP?andMGMTSTP27methylated tumors showed a clear benefit fromadjuvantPCVchemotherapy: themedianOSof CIMP? samples in the RT and RT-PCV arms was 3.27 and 9.51 years, respectively (P = 0.0033); for MGMT-STP27 methylated samples, it was 1.98 and 8.65 years. There was no such benefit for CIMP- or for MGMT-STP27 unmethylated tumors. MGMT-STP27 status remained significant in an interaction test (P = 0.003). Statistical analysis of microarray (SAM) identified 259 novel CpGs associated with treatment response. Conclusions:MGMT-STP27 may be used to guide treatment decisions in this tumor type.