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Background: The benefit of adding chemotherapy to radiotherapy RT in nely diagnosed anaplastic glioma ithout 1p19q co-deletion is unknon. The CATNON trial investigated the impact of adjuvant andor concurrent chemotherapy ith temozolomide TMZ in these tumors. Methods: Eligible ere patients ith nely diagnosed WHO grade III glioma ithout 1p19q co-deletion, 18 years, and WHO performance status PS 0-2. All patients received RT 59.4 Gy in 33 fractions, and in a 2 x 2 factorial design ere randomized to: RT alone; RT ith concurrent daily 75 mgm2 TMZ; RT folloed ith 12 cycles of 150-200 mgm2 adjuvant TMZ day 1-54 eeks; or RT ith both concurrent and 12 cycles of adjuvant TMZ. Stratification factors included O6-methyl-guanine DNA methyltransferase MGMT promoter methylation and PS. Primary endpoint as overall survival OS . 748 patients and 534 events ere needed to detect a HR reduction of 0.775 for both concurrent and adjuvant TMZ. An interim analysis as foreseen after 219 events 41 percent , and required a p value of 0.0084 for rejecting the Null hypothesis of no OS difference. Results: Beteen Dec 2007 and Aug 2015 748 patients ere randomized. On Oct 6, 2015 the interim analysis as conducted based on 221 events median follo-up: 27 months . The analysis shoed a HR reduction for OS of 0.645 95 percent CI 0.450, 0.926; p= 0.0014 after adjuvant TMZ arms iii and iv . MGMT status could be determined in 74 percent of patients, and as found methylated in 42 percent of them. MGMT methylation as prognostic for OS HR 0.54, 95 percent CI 0.38, 0.77; p= 0.001 , but at this stage did not predict improved outcome to adjuvant TMZ. For progression free survival PFS , the risk adjusted HR of adjuvant TMZ as 0.586 95 percent CI 0.472, 0.727; p lt 0.0001 . Conclusions: 12 cycles adjuvant TMZ improve OS in anaplastic glioma ithout 1p19q co-deletion. Further follo-up ill elucidate the role of concurrent TMZ . Molecular studies to address the impact of isocitrate dehydrogenase IDH mutational status and methylation profiling are ongoing. Clinical trial information: lta href=http:clinicaltrials.govshoNCT00626990 NCT00626990ltth class=border-bottom align-left rospan=2 Adjuvant temozolomideltth class=border-bottom-broken colspan=2 OSltth class=border-bottom-broken colspan=1 PFSMedian percent 5 yearMedianNo n = 372 41.1 months44.1 percent19.0 moYes n = 373 Not reached55.9 percent42.8 mo,J Clin Oncol 34, 2016 suppl; abstr LBA2000 ,NCT00626990,00:00.0,Central Nervous System Tumors