ERBB2 and breast carcinoma: HER2-positive breast cancer was more likely to be de novo stage IV, and the proportion of de novo stage IV in HER2-low breast cancer was similar to HER2-positive breast cancer and more than that in HER2-zero breast cancer in all population or HR + subgroup (Table 1, Additional file 3: Table S3 and Additional file 8: Fig. S2B).