Low Dose Dexamethasone for the Prevention of Cytokine Release Syndrome Associated With Tebentafusp

The goal of this clinical trial is to learn if a low dose of dexamethasone can prevent cytokine release syndrome in participants treated with tebentafusp for advanced uveal melanoma. The main questions the study aims to answer are: How many participants get cytokine release syndrome? How severe is the cytokine release syndrome? What other side effects happen due to dexamethasone and/or tebentafusp? Participants will be treated with tebentafusp per standard practices. For this study, participants will receive dexamethasone before infusion of the first 4 doses of tebentafusp. Participants will have visits for checkups and tests at the time they are given the medications and 9 weeks after they started. Other visits will be approximately every 6 months for at least 2 years and can be done in person or remotely (telehealth).