SYHA1815 is an orally active RET inhibitor ( IC 50 =0.9 nmol/L) with antitumor activity. SYHA1815 is more selective for RET than KDR ( IC 50 =15.9 nmol/L). SYHA1815 arrests the G1 cell cycle and inhibits RET -driven cell proliferation by downregulating c-Myc.