A selective inhibitor of the HER2, inhibiting HER2 phosphorylation with an IC₅₀ value of 6 nM; without effect on EGFR, FGFR, PDGFR, Jak1, Src, and Blk (IC₅₀ > 25 μM); inhibits the proliferation of breast, bladder, kidney, and prostate cancer cells in vitro and in vivo.