ERBB2 and breast cancer: When compared with HER2-0 tumors breast cancer, HER2-low breast cancer is a newly defined subtype of breast cancer harboring higher ERBB2 alleles and less ERBB2 hemi deletions, but there is no significant difference on genomic alterations or tumor mutation burden between HER2-low and HER2-0 breast cancer after multiple hypothesis testing.49 Interestingly, we found HRD status associates with prognosis of patients with HER2-low EBC, while no significant difference was found in the prognosis of HER-0 tumors in our study.