Pembrolizumab and EDP1503 in Advanced Melanoma

Inclusion Criteria: * Advanced, unresectable or metastatic melanoma * Be willing and able to provide written informed consent/assent for the trial. * Aged 18 years or older on day of signing informed consent. * Have measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1. * Be naïve to exposure in the metastatic setting to PD1/L1 antibody for cohort 1 but have had exposure to PD1/L1 (or PD1/L1 combination therapy) in cohort 2. Prior exposure to CTLA4 antibody in the metastatic setting is not allowed for cohort 1 though exposure in the adjuvant setting is allowed for either cohort. To be eligible for cohort 2, and considered refractory to PD1/L1, a patient must have had a restaging exam showing progressive disease at least 90 days following initiation of anti-PD1/L1 as prior therapy. * Adjuvant therapy with BRAF-MEK, PD1 or CTLA4 based therapy is allowed. Prior adjuvant BRAF-MEK therapy will fulfill treatment requirement in the metastatic setting. Patients who experience progression of disease during adjuvant PD1 therapy or within 6 months of completing adjuvant PD1 therapy will be considered refractory and thus eligible for cohort 1. Patients with progression to active metastatic disease more than 6 months following completion of adjuvant PD1 therapy will be eligible for cohort 1. * Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale. * Demonstrate adequate organ function as defined in Table …