Taletrectinib (DS-6051b) free base (25-200 mg/kg; p.o.; once daily for 18 days) shows antitumor activity. Taletrectinib free base (6.25-200 mg/kg; p.o.; once daily for 8 days) inhibits NTRK-rearranged cancer in Balb-c nu/nu mice bearing KM12 cells. Taletrectinib free base (3-100 mg/kg; p.o.; once daily for 4 days) shows rapid tumor regression in the wild-type (WT) and the G2032R-mutant Ba/F3-bearing mice without severe body weight loss.