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HER2 plays a crucial role in breast cancer (BC) progression, with the D769H and D769Y mutations significantly influencing its structural integrity, drug-binding dynamics, and therapeutic response. This study employs molecular docking and molecular dynamics simulations (MDS), with trajectories propagated for 1000 ns, to examine their distinct effects. Root mean square deviation (RMSD) analysis indicates increased conformational deviations in mutant structures, signifying heightened instability, while root mean square fluctuation (RMSF) reveals enhanced flexibility near the mutation site. Solvent accessible surface area (SASA) calculations highlight changes in solvent exposure, directly affecting ligand accessibility, while radius of gyration (Rg) assessments suggest structural loosening or tightening in response to mutation-induced alterations. Binding free energy calculations using MM-PBSA indicate variability in drug affinity, with mutations disrupting hydrogen-bonding networks and altering ligand stability. Principal Component Analysis (PCA) delineates distinct motion trajectories in mutant proteins, revealing shifts in conformational behavior. Umbrella sampling simulations indicate that while the wild-type HER2-drug complex requires 150 ps to reach equilibrium, the D769H mutant stabilizes within 100 ps, suggesting diminished drug retention. Conversely, the D769Y mutation enhances ligand binding, surpassing wild-type interaction strength. These findings elucidate mutation-specific effects on HER2 structural dynamics and drug interactions, underscoring the need for mutation-tailored therapeutic strategies to mitigate the impact of these variants.