Sargramostim (GM-CSF) + PD-1

This is an open-label phase II study looking at safety and efficacy of the combination of pembrolizumab (PD-1 inhibition and sargramostim (GMCSF) in people with unresectable stage III or IV melanoma who may have received prior immunotherapy in the metastatic setting. The U.S. Food and Drug Administration (FDA) has not approved sargramostim as a treatment option for people with stage III or IV melanoma The U.S. Food and Drug Administration (FDA) has approved pembrolizumab as a treatment option for people with stage III or IV melanoma who have received prior immunotherapy in the metastatic setting. The research study procedures include screening for eligibility and study treatment including evaluations and follow up visits. Participants will receive the study drug(s) for as long as they do not have serious side effects and their disease does not get worse and will be followed for safety 30 days after the last dose of study drug(s). Participants may also be followed for long term follow-up every 12 weeks from the last dose of study drug(s). It is expected that about 30 people will take part in this research study.