The study evaluated the efficacy and safety of larotrectinib, a highly selective TRK inhibitor, in adults and children with TRK fusion-positive cancers. A total of 55 patients, ranging from 4 months to 76 years old, were enrolled across three protocols: a phase 1 study for adults, a phase 1–2 study for children, and a phase 2 study for adolescents and adults. The primary endpoint was the overall response rate, assessed by independent review, which was 75% (95% CI, 61 to 85). According to investigator assessment, the overall response rate was 80% (95% CI, 67 to 90). At one year, 71% of responses were ongoing, and 55% of patients remained progression-free. The median duration of response and progression-free survival had not been reached. Adverse events were predominantly grade 1, with no grade 3 or 4 events considered related to larotrectinib occurring in more than 5% of patients. No patient discontinued treatment due to adverse events. The study concluded that larotrectinib demonstrated marked and durable antitumor activity in TRK fusion-positive cancers, regardless of patient age or tumor type.The study evaluated the efficacy and safety of larotrectinib, a highly selective TRK inhibitor, in adults and children with TRK fusion-positive cancers. A total of 55 patients, ranging from 4 months to 76 years old, were enrolled across three protocols: a phase 1 study for adults, a phase 1–2 study for children, and a phase 2 study for adolescents and adults. The primary endpoint was the overall response rate, assessed by independent review, which was 75% (95% CI, 61 to 85). According to investigator assessment, the overall response rate was 80% (95% CI, 67 to 90). At one year, 71% of responses were ongoing, and 55% of patients remained progression-free. The median duration of response and progression-free survival had not been reached. Adverse events were predominantly grade 1, with no grade 3 or 4 events considered related to larotrectinib occurring in more than 5% of patients. No patient discontinued treatment due to adverse events. The study concluded that larotrectinib demonstrated marked and durable antitumor activity in TRK fusion-positive cancers, regardless of patient age or tumor type.