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 opinion of the investigator, disfiguring surgery or limb
                  amputation to achieve a complete surgical resection; OR 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 with a
                  documented NTRK gene fusion (or in the case of infantile fibrosarcoma, congenital
                  mesoblastic nephroma or secretory breast cancer with documented ETV6
                  rearrangement (or NTRK3 rearrangement after discussion with the sponsor) by FISH
                  or RT-PCR or a documented NTRK fusion by next generation sequencing) (identified
                  through molecular assays as routinely performed at CLIA or other similarly
                  certified laboratories). Patients with NTRK-fusion positive benign tumors are
                  also eligible; OR Potential patients older than 21 years of age with a tumor
                  diagnosis with histology typical of a pediatric patient and an NTRK fusion may be
                  considered for enrollment following discussion between the local site
                  Investigator and the Sponsor.

          -  Patients with primary CNS tumors or cerebral metastasis

          -  Karnofsky (those 16 years and older) or Lansky (those younger than 16 years)
             performance score of at least 50.

          -  Adequate hematologic function

          -  Adequate hepatic and renal function

        Exclusion Criteria:

          -  Major surgery within 14 days (2 weeks) prior to C1D1

          -  Clinically significant active cardiovascular disease or history of myocardial
             infarction within 6 months prior to C1D1, ongoing cardiomyopathy; current prolonged
             QTc interval > 480 milliseconds

          -  Active uncontrolled systemic bacterial, viral, or fungal infection

          -  Current treatment with a strong CYP3A4 inhibitor or inducer. Enzyme-inducing
             anti-epileptic drugs (EIAEDs) and dexamethasone for CNS tumors or metastases, on a
             stable dose, are allowed.

          -  Phase 2 only:

               -  Prior progression while receiving approved or investigational tyrosine kinase
                  inhibitors targeting TRK, including entrectinib, crizotinib and lestaurtinib.
                  Patients who received a TRK inhibitor for less than 28 days of treatment and
                  discontinued because of intolerance remain eligible.