This Phase I/II trial is trying to determine the safety and recommended dose of two drugs (PD-0325901 and BGB-283) given in combination for the treatment of advanced solid cancersA Phase 1b, Open-Label, Dose-escalation and Expansion Study to Investigate the Safety, Pharmacokinetics and Antitumor Activities of a RAF Dimer Inhibitor BGB-283 in Combination With MEK Inhibitor PD-0325901 in Patients With Advanced or Refractory Solid Tumors

Exclusion

1. Central Nervous System metastasis
2. Any retinal pathology considered to be a risk factor for central serous retinopathy
3. History of glaucoma
4. Active parathyroid disorder or history of malignancy associated hypercalcemia
5. Clinically significant cardiac disease within the past 6 months of signing ICF.
6. LVEF less than 50%
7. Abnormal QT interval at Screening
8. Severe uncontrolled systemic disease
9. HIV
10. Clinically significant active or known history of liver disease. (Hepatitis B and Hepatitis C)
11. Hemorrhage or bleeding event at NCI-CTCAE v5.0 Grade 3 or higher within 28 days of first dose.
12. history of or ongoing Von Willebrand disease and/or other past or present bleeding disorders
13. Increased serum calcium
14. Inability to swallow oral medications
15. Ongoing radiation therapy or radio-cytotoxic therapy within prior 4 weeks. No chemotherapy, immunotherapy, biologic therapy, hormonal, or molecular targeted therapy within prior 2 weeks
16. Concomitant systemic or glucocorticoid therapy within 2 weeks
17. Major surgical procedure or significant traumatic injury within 4 weeks prior to first dose or anticipates need for major surgery while on study
18. Concomitant medicines that are strong CYP3A inhibitors
19. History of toxicity from another RAF, MEK, ERK inhibitor requiring discontinuation of treatment from these drugs
20. Underlying medical conditions in investigator's opinion to be unfavorable to be a part of the study
21. Has been administered a live vaccine within 4 weeks (28 days) of initiation of study treatment. NOTE: injectable seasonal vaccines for influenza and COVID-19 are generally inactivated vaccines and are allowed. Intranasal vaccines are live vaccines and are not allowed.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.