A prospective study of anti-PD-1 therapy across three types of cancer (NSCLC, melanoma, colorectal cancer) identified a notable relationship between the synchronous changes of tumor size and ctDNA levels at week 8 after treatment (r = 0.86; P = 0.002) [37], which was corroborated by subsequent findings [94]. This evidence concerns the gene PDCD1 and neoplasm.