ERBB2 and breast carcinoma: DAISY (NCT04132960), a phase II study enrolling only HER2 status breast cancer patients, reported that the median progression-free survival (mPFS) for HER2-positive cohort, HER2-low cohort, and HER2 0 cohort was 11.1 months, 6.7 months, and 4.2 months, respectively; this showed that the antitumor activity of T-Dxd correlated with HER2 expression level exhibiting a better response rate in higher HER2 expression tumors, indicating that HER2 expression level can be recognized as a possible marker of efficacy to T-Dxd [34].