Impact of IDH1 mutation status on outcome in clinical trials for recurrent glioblastoma

IDH1 mutated glioblastoma (GB) has a better prognosis than IDH1 wildtype GB. However, it remains unknown whether patients (pts) with IDH1 mutated GB have a higher 6-month progression free survival (PFS6) or radiographic response (RR) rate on clinical trials for recurrence. Retrospective review of GB pts at MDACC between 2006 and 2012 identified 330 patients in recurrent GB trials. 93 patients (28 %) had either PFS6 or a complete/partial RR per RANO criteria. 49/93 (53 %) patients with PFS6 or a complete/partial RR had tumor tissue for IDH1 testing. A matched cohort of 49 patients on recurrent GB clinical trials that failed to achieve PFS6 or RR (also with tissue for IDH1 testing) was identified for comparison. IDH1 status was obtained in 92/98 (94 %) patients of which 17 (18 %) had an IDH1 mutation. PFS6 was seen in 26/49 (53 %) patients. IDH status was unknown in two of these patients. 5/24 (21 %) were IDH1 mutated compared to 5/24 (21 %) of their matched cohort without PFS6. RR was found in 47/49 (94 %) patients. IDH status was unknown in four of these patients. IDH1 mutation was present in 7/43 (16 %) patients with RR compared to 10/43 (23 %) in the matched cohort without RR (p = 0.48). Median OS for trials at first recurrence was 9.8 months for IDH1 wildtype GB vs. 19.32 months for IDH1 mutated GB (p = 0.14). IDH1 mutation status was not predictive of PFS6 or RR in recurrent GB trials for this data set. However, further examination in larger randomized prospective studies is needed.