Mutated IDH1 is a favorable prognostic factor for type 2 gliomatosis cerebri

The prognostic significance of IDH1 mutations has been demonstrated in gliomas. It is unclear whether IDH1 mutation is also a prognostic factor in gliomatosis cerebri (GC). Primary GCs can be grouped into type 1 GCs, which have the classical diffuse growth pattern without mass formation, and type 2 GCs, which form neoplastic masses in addition to classic diffuse lesions. In this study, the prognostic relevance of IDH1/2 mutations in 74 GCs (43 type 1 and 31 type 2) was evaluated. We detected 33 (44.6%) IDH1 mutations, including R132H and R132S, by bidirectional Sanger sequencing. No mutations were detected in IDH2. The percentage of 2-year overall survival for wild-type IDH1 patients was 46 vs. 72% for patients with IDH1-mutated tumors. Mutations of IDH1 were strongly correlated with both increased overall survival (OS) and progression-free survival (PFS) in patients with type 2 GCs, and IDH1 mutations were also an independent prognostic factor predicting increased OS and PFS in type 2 GC patients in multivariate analysis. However, IDH1 mutations did not correlate with survival outcomes in patients with type 1 GCs. Finally, the subgroup of GC, which has IDH1 wild-type and additional solid component showed the worst prognosis.