Checkpoint Inhibitor Thyroiditis
Immune checkpoint inhibitors are modern cancer medicines that unleash the immune system against tumours. Because they can also unleash it against normal tissues, they frequently affect the thyroid — most often causing an underactive thyroid.
Thyroid dysfunction is one of the most common immune-related side effects of these treatments, and it is usually manageable without stopping cancer therapy.
Last medically reviewed: 15 November 2025
Key points
- Checkpoint inhibitors commonly cause thyroid inflammation and hypothyroidism.
- Thyroid function is checked before and during immunotherapy.
- Treatment is usually levothyroxine, and cancer treatment often continues.
- A transient overactive phase can occur before the thyroid becomes underactive.
What happens to the thyroid
Checkpoint inhibitors remove brakes on the immune system. In the thyroid, this can trigger inflammation — a painless thyroiditis — that may begin with a brief thyrotoxic phase as stored hormone leaks out, followed by hypothyroidism as the gland is damaged.
The pattern resembles other forms of painless thyroiditis, but the trigger is the cancer treatment.
Monitoring
Thyroid function tests are typically checked before starting immunotherapy and at intervals during treatment. Because symptoms can be non-specific, testing is the reliable way to detect it.
Unexplained fatigue, weight change, cold intolerance or palpitations should prompt earlier testing.
Management
Established hypothyroidism is treated with levothyroxine, which usually controls the problem completely. The immunotherapy can generally continue, because thyroid side effects are rarely a reason to stop it.
A thyrotoxic phase is usually monitored rather than treated with antithyroid drugs, since the gland is inflamed rather than overproducing. Beta-blockers may ease symptoms.
Coordinating care
Management is coordinated between the oncology and thyroid teams. Other immune-related side effects can occur at the same time — such as inflammation of the pituitary, which also affects thyroid tests — so a specialist review is valuable.
When to seek urgent medical help
- Severe fatigue, dizziness or fainting — possible adrenal or pituitary involvement.
- Chest pain, palpitations or breathlessness.
- Confusion, severe headache or visual changes.
This guidance does not replace emergency services. If you are seriously unwell, seek urgent medical care immediately.
Frequently asked questions
Will immunotherapy be stopped because of my thyroid?
Usually not. Thyroid side effects are generally managed with levothyroxine while cancer treatment continues. Your oncology team makes that decision.
Is the thyroid damage permanent?
Hypothyroidism caused by checkpoint inhibitors is often permanent and needs ongoing levothyroxine, but it is straightforward to manage.
Can it cause overactive thyroid?
A brief thyrotoxic phase can occur from thyroid inflammation, but true Graves’-type overactivity is less common.
How often will my thyroid be tested?
Typically before treatment and at regular intervals during immunotherapy, with extra testing if symptoms develop.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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