Beta Glucan's Effect on Pembrolizumab Immunologic Response in Stage III-IV Melanoma

This study is exploring whether adding beta-glucan (a natural supplement found in oats and mushrooms) can improve how well the immunotherapy drug pembrolizumab works in people with advanced melanoma (stage III or IV skin cancer). **You may be eligible if...** - You have been diagnosed with stage III or IV melanoma - You are currently starting or continuing pembrolizumab as a treatment and show no active signs of disease - You are 18 years or older - You are able to swallow pills - You are in good enough health to participate **You may NOT be eligible if...** - You have had an allergic reaction to beta-glucan before - You are currently taking ongoing immune-suppressing medications Talk to your doctor to see if this trial is right for you.