ERBB2 and breast cancer: Two case studies were illustrated in more detail: patient ZMB022 with stage II, HR+ HER2− breast cancer had undetected ctDNA in all follow‐up plasma samples and remained clinically stable (Fig. 5B); patient ZMB041 with stage III, HR− HER2+ subtype, had ctDNA(+) after surgery and the ctDNA level further increased after chemoradiation therapy, suggesting that she did not respond to adjuvant treatment but was clinically stable at that point.