Immunotherapy Colitis: What to Ask

Immunotherapy colitis is inflammation of the colon that can happen with immune checkpoint inhibitors. Diarrhea during immunotherapy may have more than one cause. The team may need to check for infection, for medicines, for diet changes, or for cancer-related issues too.

This page is a planning aid. It cannot diagnose the cause of a symptom, and it does not replace the instructions from your oncology team.

Diarrhea on immunotherapy is not the same as a stomach bug. The first thing your team will ask is how many loose stools you are having a day. Count them against your normal, not against zero.

• Call your care team the same day if… you are having 4 or more loose stools a day more than your usual, or diarrhea that wakes you at night.
• Call your care team the same day if… there is blood or mucus in your stool, a fever, or abdominal pain or cramping that keeps building.
• Call 911 or go to an emergency department if… you have severe abdominal pain, a rigid or very tender abdomen, are vomiting and cannot keep fluids down, or are light-headed and passing little urine. Go straight in as well for heavy rectal bleeding, a belly that is swelling and painful with no stool or gas passing, or a fever with shaking chills and a racing pulse. Untreated immune colitis can tear the bowel wall or tip into sepsis, and both need surgery or intensive care within hours.

This can begin weeks or even months after your last dose, including after treatment has finished. So tell any clinician you see that you have had immunotherapy, even if it was a while ago. Do not start anti-diarrheal medicines on your own. They can mask what your team needs to see.

Bowel inflammation can lead to dehydration, bleeding, pain, or treatment interruptions. It can also lead to medicines that calm immune inflammation. The care team needs timing, stool pattern, related symptoms, and treatment history.

Many treatment side effects are easier to handle when the team hears about them early. If your team already gave you an urgent call plan, use that plan first.

• Stool frequency compared with your usual baseline.
• Blood, mucus, severe cramping, fever, dizziness, or signs of dehydration.
• The immunotherapy drug name and your most recent infusion date.
• Recent antibiotics, laxatives, stool softeners, supplements, or diet changes.
• Fluid intake, weight change, and whether symptoms are improving or worsening.

• What is the most likely cause in my situation, and what else needs to be ruled out?
• Which symptoms or changes mean same-day contact for my exact treatment?
• What information should I track before I call or come in?
• Could this affect treatment timing, dose, or supportive medicines?
• Who should I contact after hours, and what should I say first?

The plan may include stool testing, blood work, or hydration. It may include medicines, holding immunotherapy, steroid treatment for selected cases, or gastroenterology input. Ask before taking over-the-counter diarrhea medicine during active cancer treatment.

Ask what result or symptom pattern would change the plan. Ask what can be watched, and what should not wait until the next routine visit.

• Do not assume a symptom is "just treatment" without checking the plan your team gave you.
• Do not assume the same symptom means the same thing for every cancer treatment.
• Do not start a new over-the-counter medicine, supplement, or major diet change without asking the care team while symptoms are active.

Helpful next pages include Diarrhea During Cancer Treatment and Immune-Related Side Effects. Also see Immunotherapy Pneumonitis: What to Ask, Immunotherapy Hepatitis: What to Ask, and What Is Immunotherapy? Cancer and the Immune System.