• Diagnosis during dose escalation (Phase 1) - Pathologically documented, definitively diagnosed non-resectable advanced solid tumor.

• All participants treated at doses \> 50 mg per day must have MTC, or a RET-altered solid tumor per assessment of tumor tissue and/or blood

⁃ In the expansion stage phase (Phase 2) , patients should fulfill the following criteria at Screening Patients with histologically or cytologically confirmed diagnosis of locally advanced or metastatic NSCLC, MTC, or other solid tumors.

• Subject must have a documented RET gene fusion or mutation by a CLIA certified or equivalent testing. Next-generation sequencing (NGS), quantitative polymerase chain reaction (qPCR) test or fluorescence in situ hybridization (FISH) can be used to determine molecular eligibility At least one measurable lesion as defined by RECIST 1.1, not previously irradiated and not chosen for biopsy during the screening period. Patients without RECIST 1.1 measurable disease will be eligible for enrollment in Cohort 5.

• Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1, or 2 with no sudden deterioration 2 weeks prior to the first dose of study treatment.

• Life expectancy of at least 3 months.

• Adequate organ functions.

• Ability to swallow capsules and willing and able to provide written informed consent approved by institutional review board (IRB) or independent ethics committee (IEC).

• Willingness of men and women of reproductive potential to observe conventional and effective birth control for the duration of treatment and 6 months following the last dose of study treatment; this may include barrier methods such as condom or diaphragm with spermicidal gel.