For liquid biopsies, circulating tumor‐derived DNA (ctDNA) is also an important actor which is currently approved for epidermal growth factor receptor (EGFR) mutation testing and is useful for genomic analyses.27 Alternatively, CTCs have the advantage over ctDNA of being able to measure their protein expression, which can become a target of cancer therapies.3 It is reported that the expression of programmed death 1 (PD‐1) can be detected on CTCs and potentially used to predict for efficacy.28, 29, 30. This evidence concerns the gene EGFR and cancer.