Safety, Efficacy, and Tolerability of BOS172738 in Patients With Advanced Rearranged During Transfection (RET) Gene-Altered Tumors

Inclusion Criteria

• Inclusion Criteria: Participants are eligible to be included in the study only if all of the following criteria apply: - Male or female participants must be ≥ 18 years, at the time of signing the informed consent - Diagnosis of advanced solid tumor with a documented rearranged during transfection (RET) gene altered malignancy as determined locally by a DNA based assay of tumor tissue and/or blood - Participants must have no alternative approved therapy. - For participants in Part B expansion cohort only: documented local diagnosis of either 1) advanced RET gene fusion non-small cell lung cancer (NSCLC); 2) advanced RET gene mutant medullary thyroid cancer (MTC); or 3) other RET gene altered advanced tumors or NSCLC/MTC with prior specific RET gene targeted therapy - Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 - Negative pregnancy test for females of child bearing potential; must be surgically sterile, postmenopausal, or willing and able to be compliant with a contraceptive regimen - Contraceptive use by men or women should be consistent with local regulations. - Capable of giving signed informed consent Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: - Inability to take oral medications or gastrointestinal (GI) conditions that can interfere with the swallowing or absorption of study medication - Uncontrolled or severe concurrent medical condition - History of upper GI bleeding, ulceration, or perforation within 12 months prior to the first dose of study drug - Known history of stroke or cerebrovascular accident within 6 months prior to the first dose of study drug - Participants with known infection with human immunodeficiency virus (HIV) or Acquired Immune Deficiency Syndrome (AIDS) (testing not required) - Participants who are hepatitis B surface antigen positive or participants who are hepatitis C antibody positive (Participants who have been successfully treated for hepatitis C virus [HCV] are eligible if an undetectable HCV viral load at least 6 months after completion of treatment can be demonstrated.) - Any evidence of serious active infections - Uncontrolled or severe cardiovascular disease - Uncontrolled intercurrent illness or psychiatric illness/social situations that would limit compliance with study requirements - Participants with a prior or concurrent malignancy other than the malignancies under study - Ongoing cancer directed therapy