Study Overview: This study tests a new medicine, XmAb808, combined with pembrolizumab, for people with certain types of advanced solid tumors. It's divided into two parts: finding the right dose and expanding the study to more patients. Participants will receive the medicine through an intravenous (IV) drip, which means it's given directly into the vein. The study aims to find out if the medicine is safe and how it behaves in the body.

Eligibility: To join, you must have specific advanced cancers that have spread or worsened after standard treatments. You should have a life expectancy of more than 3 months and be able to do daily activities normally. If you are already on cancer treatments or had severe reactions to past immunotherapy, you might not be eligible.

• The study involves two parts and will require multiple visits.
• Participants will receive a combination of new and existing cancer treatments.
• Potential risks include unknown side effects from the new treatment.