FMT to Convert Response to Immunotherapy

Inclusion Criteria: * Patients should be 18 years or older * Patients have pathologically confirmed advanced stage cutaneous melanoma (stage III or IV) requiring systemic treatment with anti-PD-1 * In case of stage IV disease, only patients with M1a or M1b disease are eligible. * Patients have confirmed disease progression (≥20% increase according to RECIST1.1) on two consecutive scans with a four week interval while on anti-PD-1 treatment, of which the second scan has to be performed within 3 weeks prior to signing informed consent. * Patients must have measurable disease per RECIST 1.1 criteria * Patients have an ECOG performance status of 0-1 (appendix D) * Patients have a life expectancy of \>3 months * Patients have adequate organ function as determined by standard-of-care pre-checkpoint inhibitor infusion lab (including serum ALAT/ASAT less than three times the upper limit of normal (ULN); serum creatinine clearance 50ml/min or higher; total bilirubin less than or equal to 20 micromol/L, except in patients with Gilbert's Syndrome who must have a total bilirubin less than 50 micromol/L) * Patients have an LDH level of ≤1 times ULN * Patients of both genders must be willing to use a highly effective method of birth control during treatment * Patients must be able to understand and sign the Informed Consent document Exclusion Criteria: * Patients with acral, uveal or mucosal melanoma, or patients with an unknown primary * Patients who have received treatment for their melanoma other than anti-PD-1 treatment. * Stage IV patients with M1c or M1d disease. * Patients with autoimmune diseases: patients with a history of inflammatory bowel disease, including ulcerative colitis and Crohn's disease, are excluded from this study (except Hashimoto thyroiditis, vitiligo, history of psoriasis, but no active disease) * Patients with any grade 3 or 4 immune-related adverse events still requiring active immunosuppressive medication, apart from endocrinopathies that are stable under hormone replacement therapy. Patients who had developed grade 3-4 immune related toxicity, which has reverted to grade I with immunosuppressive drugs and who are off immunosuppression at least two weeks prior to enrollment are eligible * Patients with brain or LM metastasis. * Patients with an elevated LDH level * Patients that have undergone major gastric/esophageal/bowel surgery (like Wipple, subtotal colectomy) * Severe food allergy (e.g. nuts, shellfish) * Patients with a swallowing disorder or expected bowel passage problems (ileus, fistulas, perforation) * Severe dysphagia with incapability of swallowing 2 liters of bowel lavage * Patients with a life expectancy of less than three months * Patients with severe cardiac or pulmonary comorbidities (per judgement of the investigator) * Women who are pregnant or breastfeeding * Patients with any active systemic infections, coagulation disorders or other active major medical illnesses * Patients with other malignancies, except adequately treated and a cancer-related life-expectancy of more than 5 years * Patients who received treatment with antibiotics in the three months prior to study enrolment, or patients we are expected to receive systemic antibiotics during the course of this study