Serial cf-tDNA analysis was performed on TISF of 107 evaluable patients with glioma that had paired tumor tissues, including the three major subtypes: IDH mutant without co-deletion of chromosome 1p/19q (IDH-mutant-noncodel; n = 25), IDH mutant and chromosome 1p/19q co-deleted (IDH-mutant-codel; n = 17), and IDH wild type (glioblastoma (GBM); n = 65). The gene discussed is IDH1; the disease is glioblastoma.