Forms of cancer treatment, such as radiotherapy, chemotherapy, and surgery, can damage the thyroid. This damage can lead an individual to develop hypothyroidism (an underactive thyroid).
While cancer treatments can reduce how fast some cancers spread and their effects on the body, many can also damage or remove tissue, causing side effects and other health problems. This includes hypothyroidism, a condition in which the thyroid gland cannot produce enough hormones to fulfill its usual function.
The thyroid is a butterfly-shaped gland that releases hormones to perform various crucial roles, including regulating how the body uses energy. Multiple treatments for thyroid cancers and other conditions may affect thyroid health.
Various cancer treatments may increase a person’s risk of hypothyroidism in multiple ways.
Some treatments, such as surgery or radiation,
Other treatments, including some chemotherapy drugs or medications, may block thyroid hormone production or trigger the immune system to attack the thyroid.
Treating some cancers might increase a person’s risk of hypothyroidism regardless of the treatment method. For example, a
However, the risk was highest for people who received combined chemotherapy and radiation therapy, closely followed by surgery.
Several cancer treatments can affect the thyroid and its hormones.
Radiation therapy for head and neck cancer
According to a 2023 review, hypothyroidism may occur for as many as
The review found that hypothyroidism developed within months of radiation therapy during some studies, while others showed a drop in thyroid function over several years.
A 2021 review notes the risk of hypothyroidism may relate to:
- the dose of radiation
- the type of radiation therapy a person receives
- the original size of the thyroid
- a person’s sex (females may be more likely to develop hypothyroidism)
- a person’s age (children and adolescents may be more likely to develop hypothyroidism)
The pituitary gland, located at the base of the brain, produces thyroid-stimulating hormone (TSH).
Since this hormone usually stimulates the thyroid to make thyroid hormone, surgery or radiation to remove pituitary gland tumors can also reduce thyroid hormone levels and may trigger hypothyroidism.
Surgery to remove thyroid tissue
According to the
As any treatment for thyroid cancer kills thyroid cells, the thyroid will not be able to make enough thyroid hormone following treatment. This can lead to the development of hypothyroidism.
Medication side effects
Some hormone therapy medications actively block TSH, as this hormone may increase a person’s risk of thyroid cancer developing or coming back after treatment. Blocking TSH stops the thyroid from being able to make enough thyroid hormone, leading to hypothyroidism.
For example, according to a 2019 review, people may take tyrosine kinase inhibitors (TKIs) to treat cancers of the gastrointestinal system and kidneys or directly manage progressive thyroid cancer.
This may lead to new-onset hypothyroidism in around 40% of people who take TKIs to treat cancer. However, hypothyroidism may have links to longer survival for people who take TKIs, especially in those who received a hormone replacement called levothyroxine to manage the resulting hypothyroidism.
Immunotherapy drugs
Some cancer treatments, known as immunotherapy, involve drugs that allow the immune system to target and destroy cancer cells. One particular class of immunotherapy drugs is the immune checkpoint inhibitor, which prevents cancer cells from avoiding detection by the immune system.
The American Thyroid Association advises that many people who have received an immune checkpoint inhibitor called anti-PD-1 experience thyroid inflammation. This inflammation occurs because the immune system targets thyroid tissue with specific proteins called antithyroid antibodies.
People receiving anti-PD-1 treatment may experience several months of increased thyroid activity before hypothyroidism develops. However, people who developed thyroid problems during this treatment had significantly higher cancer survival rates than those who did not 1 year after treatment.
If a treatment such as hormone therapy blocks thyroid hormone production, a person
This can help people maintain how their bodies use energy. High levels of thyroid hormone also
Does cancer cause hypothyroidism?
Some cancers may have links to hypothyroidism. For example, according to a
Other types of cancer, such as papillary thyroid cancer, may also lead to the development of hypothyroidism.
Can chemotherapy affect the thyroid?
According to a
Some cancer treatments can lead to hypothyroidism. For example, radiation therapy for head and neck cancer can damage thyroid tissue or affect the pituitary gland.
Other treatment types than can lead to hypothyroidism include surgery to remove thyroid tissue, some immunotherapy drugs that trigger an autoimmune response, and medications such as tyrosine kinase inhibitors, which block thyroid-stimulating hormone.
People who develop hypothyroidism due to cancer treatment may need to take thyroid hormone therapy for the rest of their lives.