Key Inclusion Criteria:  Subject has one of the following solid tumors which has progressed on or following at least one systemic therapy regimen administered for advanced or metastatic disease or for which no approved therapy exists:  NTRK-fusion-positive, locally advanced (i.e., not amenable to surgical resection) or metastatic solid tumor Note: Subjects with any grade of malignant glioma previously treated with systemic therapy are eligible.  Phase 1  NTRK-gene amplified, locally advanced or metastatic solid tumor EWSR1-WT1-positive DSRCTs. Subjects with NTRK-fusion-positive solid tumors other than primary brain tumors must have previously received treatment with a TRK inhibitor, unless the subject does not have access to TRK-inhibitor therapy (e.g., no TRK inhibitor is marketed and available to the subject in the subject's country) or the subject has declined treatment with available marketed TRK inhibitors. Subjects with NTRK-gene amplified solid tumors, primary brain tumors or EWSR1-WT1-positive DSRCTs may have received prior treatment with a TRK inhibitor but this is not required.  Phase 2  Has measurable disease by RECIST v1.1 for subjects with non-brain primary tumors or RANO criteria for subjects with primary brain tumors. Subjects with non-brain primary tumors must have previously received treatment with a TRK inhibitor and a documented resistance mutation(s) (e.g., solvent front, gatekeeper or xDFG mutation). Archival tissue from a prior biopsy taken after the subject completed TRK inhibitor treatment but prior to additional systemic therapy may be used to meet this eligibility criterion with Medical Monitor approval. Subjects with primary brain tumors may have received prior treatment with a TRK inhibitor but this is not required. Biopsies of brain tumors are not required for eligibility.  Key Exclusion Criteria:  Cytotoxic chemotherapy, biologic agent, investigational agent, or radiation therapy ≤ 3 weeks prior to the first dose of PBI-200 (6 weeks for nitrosoureas).  Subjects with either primary brain tumors or brain metastasis must have completed brain radiation therapy 12 weeks prior to the brain MRI obtained within 4 weeks of the first dose of PBI-200. Small-molecule kinase inhibitors or hormonal agents ≤ 14 days and within 5 half-lives prior to the first dose of PBI-200.