In particular, in 15.2% of the cases a conversion from HER2-0 to HER2-low phenotype was observed (36.4% of the HER2-0 primary breast cancer cohort), and in 14.1% of patients a change from HER2-low primary breast cancer to HER2-0 recurrent/stage IV breast cancer was found (41.2% of the HER2-low primary breast cancer cohort). This evidence concerns the gene ERBB2 and breast cancer.