IDH1 and central nervous system cancer: For these tumors that present without measurable contrast-enhancing lesions, measurable disease is defined as a clearly demarcated T2/FLAIR hyperintense lesion with a minimum short-axis diameter of 10 mm.Unlike their IDH-wildtype counterparts, IDH-mutant low-grade gliomas are characterized by slow growth and gradual treatment responses in both clinical trials and routine practice.