Inclusion Criteria:

        Phase I - Common inclusion criteria for Dose-Escalation / Dose-Expansion:

          -  Eastern Cooperative Oncology Group (ECOG) performance score of 0 or 1

          -  Available RET-gene abnormalities determined on tissue or liquid biopsy

          -  Documented progression of disease following existing therapies deemed by the
             Investigator to have demonstrated clinical benefit or unable to receive such
             therapies.

          -  Adequate hematopoietic, hepatic and renal function

        Phase I Dose-Escalation - Specific inclusion criteria:

          -  Advanced solid tumors

          -  Measurable and/or non-measurable disease as determined by RECIST 1.1

          -  If patient has brain and/or leptomeningeal metastases, (s)he should be asymptomatic.

        Phase I Dose-Expansion - Specific inclusion criteria:

          -  Locally advanced or metastatic non small cell lung cancer (NSCLC) patients with
             primary RET gene fusion and prior exposure to RET selective inhibitors

          -  Measurable disease as determined by RECIST 1.1

          -  If patient has brain and/or leptomeningeal metastases,(s)he should have:

               -  asymptomatic untreated brain/leptomeningeal metastases off steroids and
                  anticonvulsant for at least 7 days or

               -  asymptomatic brain metastases already treated with local therapy and be
                  clinically stable on steroids and anticonvulsant for at least 7 days before study
                  drug administration.

        Phase II :

          -  Available RET-gene abnormalities determined on tissue or liquid biopsy

          -  Locally advanced or metastatic:

               -  NSCLC patients with primary RET gene fusion and prior exposure to RET selective
                  inhibitors;

               -  NSCLC patients with RET gene fusion and without prior exposure to RET selective
                  inhibitors

               -  patients with advanced solid tumors that harbour RET gene abnormalities (other
                  than NSCLC patients with primary RET gene fusions) and has failed all the
                  available therapeutic options

          -  Eastern Cooperative Oncology Group (ECOG) performance score of 0-2

          -  Measurable disease as determined by RECIST 1.1

          -  If patient has brain and/or leptomeningeal metastases,(s)he should have:

               -  asymptomatic untreated brain/leptomeningeal metastases off steroids and
                  anticonvulsant for at least 7 days or

               -  asymptomatic brain metastases already treated with local therapy and be
                  clinically stable on steroids and anticonvulsant for at least 7 days before study
                  drug administration.

          -  Adequate hematopoietic, hepatic and renal function

        Exclusion Criteria:

        Common exclusion criteria for Phase 1 and Phase 2

          -  Investigational agents or anticancer therapy within 5 half-lives prior to the first
             dose of study drug

          -  Major surgery (excluding placement of vascular access) within 4 weeks prior to the
             first dose of study drug or planned major surgery during the course of study
             treatment.

          -  Whole Brain Radiotherapy within 14 days or other palliative radiotherapy within 7 days
             prior to the first dose of study drug, or persisting side effects of such therapy, in
             the opinion of the Investigator.

          -  Clinically significant, uncontrolled, cardiovascular disease including myocardial
             infarction within 3 months prior to Day 1 of Cycle 1, unstable angina pectoris,
             significant valvular or pericardial disease, history of ventricular tachycardia,
             symptomatic Congestive Heart Failure (CHF) New York Heart Association (NYHA) class
             III-IV, and severe uncontrolled arterial hypertension, according to the Investigator's
             opinion.

          -  QT interval corrected using Fridericia's formula (QTcF) >470 msec; personal or family
             history of prolonged QT syndrome or history of Torsades de pointes (TdP). History of
             risk factors for TdP

          -  Treatment with strong CYP3A4 inhibitors within 1 week prior to the first dose of study
             drug or strong CYP3A4 inducers within 3 weeks prior to the first dose of study drug.

        Phase I Dose-Expansion - and Phase II specific exclusion criteria:

          -  Presence of known EGFR, KRAS, ALK, HER2, ROS1, BRAF and METex14 activating mutations.