PDCD1 and melanoma: In patients with melanoma treated with PD-1 inhibitors alone or in combination with ipilimumab, undetectable ctDNA within 12 weeks of therapy was associated with longer PFS and OS.21 In NSCLC treated with ICIs, a ctDNA response (defined as a>50% decrease in mutant allele fraction from baseline) was significantly earlier than radiographic response and was associated with improved patient survival.22 These findings support the potential utility of post-treatment ctDNA to monitor response of camrelizumab plus GEMOX in patients with BTC.