The purpose of this study is to assess the prevention of immune checkpoint inhibitors (ICIs) related diarrhea/colitis using vedolizumab in participants with unresectable stage III or metastatic stage IV cancer, starting standard of care (SOC) immunotherapy

After being informed about the study and potential risks, all patients giving written informed consent will undergo up to a 2-week screening period to confirm their eligibility. Eligible patients will be randomized in a double-blind manner (participant and investigator) in a 1:1 ratio to Vedolizumab or placebo and given their first dose within 2 weeks of starting their SOC immunotherapy. Vedolizumab or placebo will be administered at Weeks 0, 2, 6, 14, and 22.

Inclusion Criteria:

• Signed informed consent prior to initiation of any study specific activities or procedures
• Diagnosed with unresectable advanced stage III or metastatic stage IV malignancy
• Planned for initiation of SOC immunotherapy and development of prognostic biomarker evidence that predisposes to ICI diarrhea/colitis risk
• Ability to and willingness to adhere to the randomized treatment interventions (vedolizumab or placebo), administered intravenously

Exclusion Criteria:

• Condition(s) for which vedolizumab is contraindicated (e.g., hypersensitivity reaction, known allergic reaction to vedolizumab or its components)
• Current or prior use of vedolizumab or prior immunotherapy exposure for cancer
• Presence of inflammatory bowel disease (Crohn's disease, ulcerative colitis), indeterminate colitis, or microscopic colitis
• Presence of ileostomy, colostomy, or short bowel syndrome
• Presence of known luminal gastrointestinal metastases at baseline
• Presence of significant pre-existing autoimmune disease (at investigator's discretion)
• Presence of severe infection(s) or opportunistic infection(s)
• Active enteric infection with viral, bacterial, or parasitic pathogens
• Presence of untreated latent or active tuberculosis, or untreated chronic hepatitis B virus
• Baseline ECOG status grade ≥3
• Pregnancy or lactation
• Treatment with another investigational product within 8 weeks of randomization
• Requirement for baseline anti-diarrheal treatment(s) (including but not limited to loperamide, diphenoxylate-atropine, octreotide, tincture of opium), anticholinergic drug(s), or opioid-based analgesic(s) used specifically for diarrhea control within 14 days of randomization
• Any condition or diagnosis, that could in the opinion of the Qualified Investigator or delegate interfere with the participant's ability to comply with study instructions, might confound the interpretation of the study results, or put the participant at risk