Inclusion Criteria:

          -  Advanced solid tumor for which, in the opinion of the investigator, no other standard
             therapy offers greater benefit.

          -  A solid tumor diagnosis in the setting of:

               -  a) a documented NTRK fusion and a clinical history of relapse following a
                  response to a prior TRK inhibitor

               -  b) a documented NTRK fusion unresponsive to a prior TRK inhibitor

               -  c) a documented NTRK fusion and a clinical history of intolerance to a prior TRK
                  inhibitor

          -  NTRK gene fusions will be identified in a CLIA-certified (or equivalently-accredited
             diagnostic) laboratory. If such a report cannot be provided, other available
             certifications/accreditations are required and need to be documented. Patients with
             infantile fibrosarcoma (IFS) or congenital mesoblastic nephroma (CMN) may be enrolled
             based on an ETV6+ FISH test without identifying NTRK3.

          -  Performance Status: Eastern Cooperative Oncology Group (ECOG) score ≤ 2 in adults or
             Karnofsky Performance Score (KPS) Score≥50% (age ≥ 16 years) or Lansky Performance
             Score (LPS) ≥ 40% (age < 16 years).

          -  Life expectancy of at least 3 months.

          -  Adequate hematologic, hepatic and renal function.

          -  Patients with stable central nervous system (CNS) primary tumor, brain metastases, or
             treated spinal cord compression are eligible if neurological symptoms have been stable
             for 7 days prior to the first dose of selitrectinib.

          -  Ability to receive study drug orally or by enteral administration

        Exclusion Criteria:

          -  Prior exposure to second generation TRK inhibitor (e.g. selitrectinib, repotrectinib
             (TPX-0005)), taletrectinib (DS-6501b/AB-106)). Exception is in case patient presented
             intolerance to the second generation TRK inhibitor agent and the duration of exposure
             was less than 28 days. No previous treatment with selitrectinib is allowed.

          -  Concurrent treatment with a strong CYP3A4 inhibitor or inducer, consumption of
             grapefruit juice or Seville oranges, or drugs associated with QT prolongation.

          -  Clinically significant active cardiovascular disease or history of myocardial
             infarction within 3 months prior to planned start of selitrectinib, or prolongation of
             QT interval corrected for heart rate (QTc interval) >480 milliseconds within past 6
             months

          -  Major surgery within 7 days of enrollment

          -  Uncontrolled systemic bacterial, fungal or viral infection.

          -  Pregnancy or lactation.

          -  Known hypersensitivity to selitrectinib or Ora-Sweet® SF and OraPlus® for patients
             receiving liquid formulation.