ERBB2 and neoplasm: In the DB-04 study, the PFS benefit of T-Dxd was consistently observed in patients with HER2 IHC 1+ (10.3 months) and IHC 2+/ISH-negative disease (10.1 months) [12], indicating the number of HER2 receptor molecules in the IHC 1+ tumor cell membrane (~100,000 molecules) reached the threshold for the unique bystander killing effect of T-Dxd in HER2-low expressing tumors.