A Study to Test the Safety and Efficacy of the Drug Larotrectinib for the Treatment of Tumors With NTRK-fusion in Children

Inclusion Criteria: * Phase 1 (Closed): * Dose escalation: Birth through 21 years of age at C1D1 with a locally advanced or metastatic solid tumor or primary CNS tumor that has relapsed, progressed or was nonresponsive to available therapies and for which no standard or available systemic curative therapy exists; OR Infants from birth and older with a diagnosis of malignancy and with a documented NTRK fusion that has progressed or was nonresponsive to available therapies, and for which no standard or available curative therapy exists; OR Patients with locally advanced infantile fibrosarcoma who would require, in the opinion of the investigator, disfiguring surgery or limb amputation to achieve a complete surgical resection. Phase I dose escalation cohorts are closed to enrollment. * Dose expansion: In addition to the above stated inclusion criteria, patients must have a malignancy with a documented NTRK gene fusion with the exception of patients with infantile fibrosarcoma, congenital mesoblastic nephroma or secretory breast cancer. Patients with infantile fibrosarcoma, congenital mesoblastic nephroma or secretory breast cancer may enroll into this cohort with documentation of an ETV6 rearrangement by FISH or RT-PCR or a documented NTRK fusion by next generation sequencing. * Phase 2: \-- Infants from birth and older at C1D1 with a locally advanced or metastatic infantile fibrosarcoma, patients with locally advanced infantile fibrosarcoma who would require, in the op…