The ERBB2 gene encodes the HER2 protein, a receptor tyrosine kinase belonging to the ERBB family. Overexpression or amplification of ERBB2 is strongly associated with aggressive cancers, particularly breast cancer, where it drives tumor growth, metastasis, and resistance to therapy. Recently, emerging studies have identified a specific mutation in ERBB2, termed YVMA (c.3769G>A; p.Y1257N), which occurs in the kinase domain of the protein. This mutation stabilizes HER2’s active conformation, enhancing oncogenic signaling even in the absence of ligand binding. Clinically, YVMA mutations are linked to poorer prognosis in gastric and breast cancers and have been shown to confer resistance to conventional HER2-targeted therapies like trastuzumab. Understanding YVMA-driven mechanisms may inform novel therapeutic strategies, such as next-generation tyrosine kinase inhibitors (TKIs), to combat treatment-resistant tumors.