Tucatinib is an oral biological inhibitor of the human epidermal growth factor receptor tyrosine kinase ErbB-2 (also known as HER2) with potential anti-tumor activity. Tucatinib selectively binds to ErbB-2 and inhibits its phosphorylation, which may block the activation of the ErbB-2 signaling pathway, leading to growth inhibition and death of tumor cells expressing ErbB-2. ErbB-2 is overexpressed in various cancers and plays an important role in cell proliferation and differentiation.