CancerSnoop immunotherapy side effects guide featuring a woman at home looking at her phone, with the headline “When should you call?

Immunotherapy Side Effects: Which Symptoms Should You Report?

CancerSnoop · Cancer Guides

A new symptom deserves a call.

Some immunotherapy side effects start with symptoms that seem ordinary: diarrhea, a rash, cough or unusual tiredness. Reporting changes early helps your team assess what is happening.

This guide covers immune checkpoint inhibitors, not every form of immunotherapy.

Why can checkpoint inhibitors cause side effects?

These medicines release immune-system brakes to help attack cancer. The activated immune response can also affect healthy tissues. Inflammation may involve the skin, bowel, lungs, liver, kidneys, hormone-producing glands, heart or nervous system. Reference 1.

Seek emergency care now

Call your local emergency number or seek emergency care for:

Severe breathing difficulty or chest pain.
Collapse, a seizure or new confusion.
Rapidly worsening weakness, especially with difficulty swallowing or breathing.
Severe abdominal pain, heavy bleeding or signs of severe dehydration.

Do not wait for your next oncology appointment. Tell emergency staff you receive—or previously received—a checkpoint inhibitor. Reference 3.

Which symptoms should you report promptly?

Contact your oncology team’s urgent advice line for new or worsening symptoms, including:

Bowel changes: diarrhea, more stools than usual, blood or mucus, or abdominal pain.
Breathing changes: a new cough or breathlessness.
Skin changes: a spreading rash, blistering or mouth sores.
General changes: unusual fatigue, dizziness, persistent headache, fever or vomiting.
Other changes: yellow skin or eyes, reduced urination, excessive thirst or frequent urination.

Follow your team’s specific instructions. Worsening or severe symptoms may require emergency assessment. Reference 1 and Reference 3.

Symptoms do not confirm the cause

An infection, another medicine or the cancer itself can cause similar problems. Do not assume a symptom is an immune reaction—or dismiss it as a routine treatment effect. Clinical assessment helps distinguish the causes.

Can problems begin after treatment ends?

Yes. Immune-related problems can develop during treatment or after it has stopped. Keep the drug name and last treatment date available, and mention previous immunotherapy when another clinician assesses a new symptom. Reference 3.

How are immunotherapy side effects assessed?

Your team considers the symptom pattern, examination and relevant tests. Depending on the suspected organ, assessment may involve blood tests, imaging or specialist input. Management depends on the affected organ and severity. Reference 2.

Reporting a symptom does not automatically end treatment

Some mild reactions can be monitored. Others require a treatment pause, corticosteroids or additional treatment. Severe reactions may require permanent discontinuation. Some hormone-related problems need hormone replacement. These decisions belong to your treating team. Reference 2.

Make the call easier

Have these details ready:

Your immunotherapy name and last dose date.
When the symptom started and whether it is worsening.
How it differs from your usual baseline.
Your temperature, if measured, and other medicines taken.

Before leaving the clinic, ask which number to use outside normal hours.

Do not self-treat a suspected immune reaction

Do not independently start steroids or change prescribed treatment. Ask your oncology team before trying to manage a suspected immune-related problem with over-the-counter medicines. Treatment needs to match the cause and severity. Reference 2.

Questions for your care team

Which symptoms require an immediate call with my particular medicine?
What fever threshold should I follow?
Should I carry an immunotherapy alert card?
What follow-up is needed after my last dose?

Treatment selection is a separate question from side-effect monitoring. For an example of how tumor features inform treatment discussions, see Understanding Your Breast Cancer Results.

CancerSnoop Bottom Line

Report changes early. Know your emergency plan.

New symptoms deserve attention during and after checkpoint inhibitor treatment. Use your oncology advice line promptly, and seek emergency care for severe warning signs.

References

Reference 1
National Cancer Institute.
Immune Checkpoint Inhibitors.

Reference 2
Schneider BJ, et al.
Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: ASCO Guideline Update.
Journal of Clinical Oncology. 2021.
DOI: 10.1200/JCO.21.01440. PMID: 34724392.

Reference 3
Brahmer JR, et al.
Society for Immunotherapy of Cancer (SITC) Clinical Practice Guideline on Immune Checkpoint Inhibitor-Related Adverse Events.
Journal for ImmunoTherapy of Cancer. 2021.
DOI: 10.1136/jitc-2021-002435. PMID: 34172516.

Last reviewed: November 3, 2026.
Educational information only. Follow your treating team’s individualized instructions. The symptom lists are not exhaustive.