Effect of Diet on the Immune System in Patients With Stage III-IV Melanoma Receiving Immunotherapy, DIET Study

This phase II trial investigates the possible immune effects of two different diets targeting the gut microbiome in patients with stage III-IV melanoma that has been removed by surgery (resectable), has spread to other places in the body (metastatic), or is unable to be removed by surgery (unresectable), and who are being treated with the immunotherapy drugs pembrolizumab or nivolumab as part of their standard of care. Both diets are whole foods diets that meet the American Cancer Society recommendations for cancer patients, but they will vary in fiber content. The purpose of this trial is to learn about the effects of dietary interventions on the structure and function of the gut microbiome in patients with melanoma being treated with standard of care immunotherapy (pembrolizumab or nivolumab).