It is important to note that our study focuses on de novo metastatic HER2-positive breast cancer only, which, in prior studies, has had better survival outcomes compared to recurrent or relapsed metastatic HER2-positive breast cancer, especially in patients with a metastasis-free interval of ≤24 months likely due to differences in demographics, cancer characteristics/ biology, and exposure to prior treatments [12,13]. This evidence concerns the gene ERBB2 and breast cancer.