Cancer and cancer treatment can cause problems in the body's thyroid gland. When your thyroid is not working properly, you may be getting too much or too little of important hormones that this gland makes.
When the thyroid makes too many hormones, it is called overactive thyroid or hyperthyroidism. When the thyroid does not make enough hormones, this is called an underactive thyroid or hypothyroidism.
What is the thyroid?
The thyroid is a small gland located in the front of the neck. It produces hormones by taking in iodine from the bloodstream. These hormones send messages to other parts of the body and tell them what to do. For example, hormones from the thyroid gland help maintain your body temperature, metabolism, and other functions. When you have a thyroid problem, these processes may not happen in the way they should. This imbalance can cause a variety of symptoms and problems.
What are the signs and symptoms of thyroid problems?
What you feel when you have a thyroid problem depends on if you have an underactive thyroid or an overactive thyroid.
Signs of an underactive thyroid (hypothyroid) include:
Dry skin and hair
Mood changes, like feeling sad, depressed, or less interested in life than usual
Signs of an overactive thyroid (hyperthyroid) include:
Chest pain, fast heart rate, or irregular heartbeat
Feeling hot and sweaty
Swelling or tenderness in the neck
Tremors or shaking
If you have any of the symptoms listed above, tell your doctor or health care team right away. Often, the symptoms of a thyroid problem can look like the symptoms of other conditions. Relieving side effects is an important part of cancer care and treatment. It is called palliative care or supportive care.
What causes thyroid problems when you have cancer?
Thyroid problems have many causes. Thyroid problems can happen on their own, whether you have cancer or not. They are more common as you get older. However, thyroid problems are also a common side effect of certain types of cancer and cancer treatment.
The types of cancer and cancer treatment that raise your risk of thyroid problems include:
Thyroid cancer. Removing part or all of the thyroid gland is the main treatment for this type of cancer. This causes thyroid hormone levels to drop. The hormones are replaced with medication.
Radiation therapy to the head, neck, or upper spine. This is one of the most common causes of thyroid problems after cancer treatment. Whole-body radiation can also cause thyroid problems.
Chemotherapy. Chemotherapy, especially in high doses before a bone marrow transplant (stem cell transplant), can cause thyroid problems.
Targeted therapy. Targeted therapy is a treatment that affects specific biomarkers in the cancer. Treatments called tyrosine kinase inhibitors, or TKIs, are an example of targeted therapies that can affect your thyroid gland. This includes the drugs sunitinib (Sutent), sorafenib (Nexavar), imatinib (Gleevec), nilotinib (Tasigna) and others.
Immunotherapy. Immunotherapy is a treatment that boosts your body's natural defenses to fight cancer. Some immunotherapy treatments can affect your thyroid. Interferon-alpha is an example of an immunotherapy drug that may lower thyroid functioning.
Radiation therapy with radioactive iodine (RAI or I-131). A healthy thyroid gland uses iodine to make its hormones. Radioactive iodine upsets the normal thyroid process.
Cancer treatment can also cause non-cancerous (benign) lumps called nodules on the thyroid gland. It can also cause second cancers.
How are thyroid problems diagnosed?
To check for thyroid problems, your health care provider may do the following during your follow-up care:
Examine your neck. They thyroid is in the front part of your neck, just above your voice box (larynx). Your doctor will press on this area gently to feel for changes.
Do blood tests. Your doctor will check a sample of your blood to measure your thyroid hormone levels.
If your body is still growing, check for normal growth. Some treatments for childhood cancer cause thyroid problems, and these can disrupt the growth process.
If you plan to become pregnant, it's important to check for thyroid problems. Thyroid problems can harm your unborn child. While pregnant, you will need regular thyroid checks as well.
How are thyroid problems prevented and treated?
If your cancer treatment could affect your thyroid gland, your doctor will check your thyroid hormone levels before treatment begins. You may be able to take medicine before some cancer treatments to help prevent thyroid problems.
Treatment for your thyroid problems depends on if you have an overactive or underactive thyroid. You may need to talk with an endocrinologist, which is a doctor who specializes in treating problems with hormones, glands, and the endocrine system.
Underactive thyroid (hypothyroidism). The treatment for an underactive thyroid is artificial thyroid hormone medication, given as a pill you swallow. You take the pill at the same time every day. Usually, you will need to take this pill daily for the rest of your life.
Sometimes, low thyroid function after radiation therapy can get better. If so, you would stop taking medicine when your thyroid gland starts to work well again.
Overactive thyroid (hyperthyroidism). Treatment for high thyroid levels includes medication. If you have a non-cancerous nodule on your thyroid or thyroid cancer, treatment options include surgery or radioactive iodine treatment. Treatment destroys thyroid tissue so it cannot produce hormones.
Questions to ask the health care team
Consider asking the following questions:
Do I have an increased risk of thyroid problems, due to the cancer or its treatment? For other reasons?
How will my thyroid function be checked? How often?
What can be done to prevent thyroid problems before cancer treatment begins?
What signs or symptoms should I watch for?
Who should I call if I have any signs of a thyroid problem?
Why is it important to treat thyroid problems?
What is the treatment for my thyroid problem?
Long-Term Side Effects of Cancer Treatment
What You Need to Know About Immunotherapy Side Effects
American Thyroid Association: What You Need to Know About the Thyroid