Inclusion Criteria:  ≥ 18 years old Patient has been treated with immune checkpoint inhibitors (ICI), including anti-CTLA-4, anti-PD-1 and anti-PDL-1 therapy for any malignant indication Patient has developed diarrhea ≥ Grade 2 attributed to ICI Patient has diarrhea ≥ Grade 2 attributed to ICI, that persists despite treatment with corticosteroids for at least 72 hours and/or at least one dose of a biologic medication, such as infliximab or vedolizumab, with symptoms that persist or recur at least 72 hours post-infusion ° If no to the above, patient has a contraindictation to immunosuppressive treatment  Exclusion Criteria:  Active GI infection, including untreated viral, bacterial or fungal or alternative identified cause(s) of diarrhea. Antibiotic exposure within 48 hours prior to FMT  Expected prolonged compromised immunity indicated by at least one of the below:  Known HIV infection with CD4 count <240 ANC <1000/mm3 (use of growth factors to raise ANC is acceptable) Seronegative for EBV or CMV (i.e. EBV IgG negative or CMV IgG negative)  Contraindications to anesthesia for procedure indicated by at least one of the below:  Serious cardiopulmonary comorbidities Inability to tolerate anesthesia  Pregnancy  Patient is pregnant Women of childbearing potential should not have plans to became pregnant or breastfeed an infant and must agree to use a highly effective method of birth control until 2 months after treatment with FMT (e.g. barrier method, oral or parenteral contraceptives, a vasectomized partner, or abstinence from sexual intercourse) Severe food allergies