We used targeted capture sequencing to analyze TP53‐mutated circulating tumor DNA (ctDNA) in metastatic breast cancer patients and to determine whether TP53 mutation has predictive value for anti‐human epidermal growth factor receptor 2 (HER2) treatment for in HER2 amplification‐positive patients (HER2+) and HER2 mutation‐positive, amplification‐negative (HER2−/mut) patients. The gene discussed is ERBB2; the disease is breast carcinoma.