In samples from patients with advanced metastatic breast cancer (cohorts B and C), we obtained 98.0 % and 97.1 % concordance and an AKT1E17K mutation capture rate of 66.7 % and 85.7 % for ctDNA, and 100 % concordance and a PIK3CA mutation capture rate of 100 % (cohort B). The gene discussed is PIK3CA; the disease is breast cancer.