The most mutated genes in tumor samples and CSF ctDNA were TERT, TP53, EGFR, PTEN, PIK3CA, and PDGFRA (Figure 3C), which were completely shared in 18 patients, yielding an overall concordance rate of 81.8% between tumor and CSF ctDNA samples (Figure 3D). Here, PIK3CA is linked to neoplasm.