This study tests a new drug, XmAb808, with pembrolizumab, a medicine already used for cancer. It's for people with advanced cancers like prostate, lung, or skin cancer. The study checks if the drug is safe and how it works in the body. Participants will get the medicine through a needle in their vein, called intravenous (IV) administration. The study has two parts: finding a safe dose (Part A) and testing it on more people (Part B).

To join, you must have certain types of cancer that didn't improve with other treatments. You must also have a life expectancy of more than 3 months and be able to do daily activities. You can't join if you're on other cancer treatments, had specific past treatments, or have active brain cancer.

• The study involves multiple visits for treatment and testing.
• There might be side effects as the drug is new.
• Participants are not receiving any compensation.