This study will be conducted to assess the safety and tolerability of BOS172738 when administered to patients with advanced solid tumors with rearranged during transfection (RET) gene alterations and also to establish the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) of BOS172738.
In Part A (dose escalation), participants with advanced solid tumors with rearranged during transfection (RET) gene alterations will receive oral BOS172738 at a starting dose of 10 milligrams (mg) once daily in each 28-day cycle. In Part B (dose expansion), participants with RET gene-fusion non-small cell lung cancer (NSCLC), with RET gene-mutant medullary thyroid cancer (MTC), and with RET gene-altered advanced tumors or NSCLC/MTC with prior specific RET gene-targeted therapy will be enrolled in Cohorts 1, 2, and 3, respectively, and will receive oral BOS172738 once daily in each 28-day cycle at the recommended Phase 2 dose (RP2D) established in Part A.
Participants must have no alternative approved therapy.
Contraceptive use by men or women should be consistent with local regulations.