It was found that the mutations of cancer-associated genes occurred in all 62 CSF ctDNA samples, with the highest frequency on TP53 (54/62, 87.10%), EGFR (44/62, 70.97%), PTEN (39/62, 62.90%), CDKN2A (32/62, 51.61%), APC (27/62, 43.55%), and TET2 (27/62, 43.55%). The gene discussed is APC; the disease is cancer.