RecruitingPhase 1Biological interventionDetermine Safety & Recommended Phase 2 Dosing of Zeaxanthin Alone or in Combination w/Pembrolizumab in Patients With Metastatic CancerThe purpose of the research is to determine the highest dose of an oral compound called zeaxanthin that can be safely taken each day in patients with advanced cancer, the toxicity profile of zeaxanthin, and the dose of zeaxanthin to use in future cancer clinical trials.