G-NK cells are associated with improved OS and PFS in trastuzumab-treated patients from both clinical trials and real-world datasets, suggesting their presence may serve as a predictive marker for treatment efficacy. Adoptive transfer of g-NK cells is being explored to augment the efficacy of therapeutic monoclonal antibodies. >Datasets used in analyses: CALGB 40601 trial, C1-2 and C5; Finland Herceptin trial, C3-4 and C6-7; Molecular Taxonomy of Breast Cancer International Consortium, C8; Tempus Labs, RWD1-2.