This is a clinical pilot study using oral beta-glucan on patients with advanced stage III-IV melanoma without evidence of disease receiving adjuvant Pembrolizumab. The aim is to see whether beta-glucan treatment in combination with Pembrolizumab may provide augmented immunologic phenotypes such as decreased peripheral MDSCs, enhanced T effector cell function, or enhanced cytokine production in the peripheral blood or plasm of enrolled subjects. Secondary outcome measures will include clinical endpoints such as recurrence, progression free survival and overall survival.