ERBB2 and breast cancer: The phase III DESTINY-Breast04 study, the first to focus on HER2-low breast cancer and yield positive results, demonstrated that DS-8201a significantly prolonged progression-free survival (PFS) and OS in HER2-low metastatic breast cancer (MBC) patients compared to the physician’s choice of chemotherapy, regardless of hormone receptor (HoR) status (HoR+: mPFS: 10.1 vs. 5.4 months, p<0.001; mOS: 23.9 vs. 17.5 months, p=0.003; HoR-: mPFS: 8.5 vs. 2.9 months; mOS: 18.2 vs. 8.3 months) (21).