In view of the development regarding new classification of HER2 status, the comparative effectiveness of HER2-low breast cancer patients from treatment by T-DXd, and the outstanding value of CNB among patients with advanced cancer or those before neoadjuvant therapy, it is urgent for us to further verify the concordance of CNB and SEB, especially to evaluate the diagnostic value of CNB among patients with HER2-low breast cancer. The gene discussed is ERBB2; the disease is cancer.