ERBB2 and breast cancer: Initial data from the DAISY trial (Study of DS-8201a, an Antibody Drug Conjugate for Advanced Breast Cancer Patients, With Biomarkers Analysis (DAISY) (ClinicalTrials.gov Identifier: NCT04132960), suggest that patients with tumours that display very low levels of HER2 expression (currently regarded as score 0) may still benefit from T-DXd therapy.