The goal of this clinical trial is to learn if KQB168 works to treat advanced solid tumor cancer in adults. It will also learn about the safety of KQB168. The main questions it aims to answer are:

• What is the safe dose of KQB168 by itself or in combination with pembrolizumab?
• Does KQB168 alone or in combination with pembrolizumab decrease the size of the tumor?
• What happens to KQB168 in the body?

Participants will:

• Take KQB168 daily, alone or in combination with pembrolizumab
• Visit the clinic about 8 times in the first 8 weeks, and then once every 3 weeks after that

Inclusion Criteria:

• Histologically confirmed diagnosis of solid tumor malignancy.
• Unresectable or metastatic disease that has progressed on immunotherapy.
• No available treatment with curative intent
• Adequate organ function
• Measurable disease per RECIST v1.1

Exclusion Criteria:

• Active primary central nervous system tumors
• Cardiac abnormalities
• History of lung diseases
• Any condition that may impair drug absorption or prevent oral dosing
• Known history of immune-mediated colitis and uncontrolled autoimmune diseases