Considering 2,008 women with metastatic HER2-positive breast cancer in 2016 and on the basis of the median overall survival results, mortality rates of 50, 25, and 18 deaths per month were estimated for the treatment arms chemotherapy alone, chemotherapy plus trastuzumab, and chemotherapy plus trastuzumab and pertuzumab, respectively. This evidence concerns the gene ERBB2 and breast cancer.