RecruitingPhase 1Drug trialY-NM600 in Patients Receiving Anti-PD-1 or Anti-PD-L1 for Metastatic CancerParticipants with metastatic cancer who are taking anti-PD-1 or anti-PD-L1 therapy will be enrolled to assess the safety of and find the optimal dose for radioactive imaging agents and to explore whether these agents will make current drug therapies work better. Up to 60 participants will be enrolled and can expect to be on study for up to 9 months.