When we looked at the tumor characteristics, the association was significant only among those with aggressive tumor phenotypes at baseline, including glioblastoma (OR = 2.24, 95% CI = 1.31-3.92), high-grade glioma (OR = 1.78, 95% CI = 1.19-2.89), and IDH1 mutation–negative glioma (OR = 1.67, 95% CI = 1.04-3.15). This evidence concerns the gene IDH1 and central nervous system cancer.