A First-in-human Study to Evaluate the Safety, Tolerability and Pharmacokinetics of DS-6051b

Inclusion Criteria: 1. Histologically or cytologically confirmed diagnosis of advanced solid tumors that have relapsed from or are refractory to standard treatment or for which no standard treatment is available 2. Part 1 Dose Escalation subjects must meet 1 of the following criteria: * Solid tumors with documented ROS1, NTRK1, NTRK2, or NTRK3 rearrangement * Neuroendocrine tumors * Solid tumors with tumor-induced pain 3. Part 2 Dose Expansion subjects must meet 1 of the following criteria: * NSCLC with documented ROS1, NTRK1, NTRK2, or NTRK3 rearrangement * k-RAS wild-type CRC with documented NTRK1, NTRK2, or NTRK3 rearrangement * Other solid tumors with documented ROS1, NTRK1, NTRK2, or NTRK3 rearrangement * Pulmonary LCNEC; 4. Male or female ≥18 years of age 5. Eastern Cooperative Oncology Group performance status 0 to 1 6. Adequate organ function 7. Adequate blood clotting function 8. Women of childbearing potential must have a negative pregnancy test 9. Willingness to provide archival tumor samples 10. Other inclusion criteria may apply Exclusion Criteria: 1. Hematological malignancies 2. Known positive HIV infection, or active hepatitis B or C infection 3. Comorbidity that would interfere with therapy 4. Receipt of an allogeneic bone marrow or allogeneic stem cell transplant 5. Concomitant medical condition that would increase the risk of toxicity, in the opinion of the Investigator or Sponsor 6. History of myocardial infarction and unstable angina within 6 months before study drug treatment; symptomatic congestive heart failure (Congestive Heart Failure New York Heart Association Class III or IV); congenital long QT syndrome; or ventricular arrhythmias defined as grade ≥2 according to NCI CTCAE, v4 7. Clinically active primary central nervous system tumors or brain metastases with the exception of subjects with glioblastoma multiform that carry ROS1 rearrangement 8. Unresolved toxicities from previous anticancer therapy 9. Systemic treatment with anticancer therapy within 3 weeks before study drug treatment 10. Therapeutic radiation therapy or major surgery within 4 weeks before study drug treatment or palliative radiation therapy within 2 weeks before study drug treatment 11. Participation in a therapeutic clinical study within 3 weeks for biological treatments, and within 2 weeks or 5 half-lives, whichever is longer, for small molecule agents, before study drug treatment 12. Concomitant treatment with strong inhibitors or inducers of CYP3A4 and P-glycoprotein 13. Clinically significant malabsorption syndrome or other gastrointestinal disease that would impact drug absorption 14. QTcF values higher than 450 ms at screening 15. Breastfeeding 16. Other exclusion criteria may apply