In the present study, we addressed this question for the first time by performing a direct comparison study of PIK3CA mutational status (E545K, H1047R) in DNA isolated from CellSearch® cartridges and paired plasma‐ctDNA from the same blood draws in early and metastatic BrCa, using our previously described highly sensitive real‐time PCR methodology (Markou et al., 2014). The gene discussed is PIK3CA; the disease is invasive breast carcinoma.