We utilized a small cohort of IDH-mutant astrocytomas (n = 42) with known CIN or CS status to identify epigenetic differences between the two groups, and then applied this method using an unbiased approach to a larger cohort of publicly-available IDH-mutant astrocytomas (n = 245) to verify these epigenetic signatures and investigate the clinical and molecular differences between cases clustering as CIN or CS by methylation profiling. Here, IDH1 is linked to Cowden syndrome 1.