This study seeks to deepen understanding of HER2 negative and low patients for tailored treatment by determining the 3-year disease-free survival (DFS) rates and prognostic variables of different subsets of HER2 negative (HER2 0) and HER2-low breast cancer patients (HER2 +1, HER2 +2 and HER2 FISH negative). This evidence concerns the gene ERBB2 and breast cancer.