- Participants with treated brain metastases are allowed. Radiation must be completed at least 2 weeks prior to pembrolizumab dosing and participants must not require ongoing steroids. Participants with untreated brain metastases that are all <5 mm with no clinical symptoms or vasogenic edema may be allowed on study on a case-by-case basis on discussion with sponsor. These participants will require MRI monitoring every 6 weeks to ensure stability.