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