ERBB2 and breast carcinoma: Regarding prognosis, some reports have shown no difference between HER2-low and HER2-zero breast cancer [20, 21, 24, 25, 30, 36, 38–41], while others have shown that HER2-low breast cancer had better prognosis than HER2-zero breast cancer [22, 27, 29, 34, 42–47].