ERBB2 and breast cancer: In 18 of the cases (5.0%), HER2 status had changed from HER2-0 in primary tumor to HER2-low in metastatic lesions (23.1% of the HER2-0 primary breast cancer cohort), and in 17 of the cases (4.7%), HER2 status had changed from HER2-low to HER2-0 (13.7% of the HER2-low primary breast cancer cohort).