Thyroid Hormones and Cancer

Key Points

  • Thyroid hormones are key players in normal growth, development and metabolism and seem to play a role in the development of some human cancer types.
  • For optimal thyroid function, appropriate amounts of iodine must be available to the thyroid.
  • Disorders in thyroid hormones are associated with increased risk of some cancer types including colorectal cancer, liver cancer, and thyroid cancer.
  • Hormone levels and interactions may also support cancer progression by dampening immune responses.
  • Thyroid hormone supplementation is associated with decreased risk of colorectal cancer, though supplementation may interfere with colon cancer drug treatments.
  • The body's ability to use thyroid hormones—its bioavailability—can affect cancer development and spread.
  • Reducing thyroid hormones with chemical treatment or inhibiting their ability to bind to receptors present possibilities for future treatment pathways.

Thyroid hormones are key players in normal growth, development and metabolism, as well as bone and brain development during pregnancy and infancy. They also seem to play a role in the development of some human cancer types. 

Food and Thyroid Hormones

Foods rich in iodine:1

  • Fish such as cod and tuna, seaweed, shrimp, and other seafood
  • Dairy products
  • Grains
  • Fruits and vegetables, although the amount varies with the iodine in the soil and fertilizer used where grown
  • Iodized salt; processed foods such as canned soups almost never contain iodized salt

Zinc and vitamins A and E support the proper manufacture of thyroid hormones. Good sources:2

  • Some types of seafood (oysters, crab, lobster)
  • Beef
  • Chicken (dark meat)
  • Pumpkin seeds
  • Cashews
  • Chickpeas
  • Oats

Three key hormones act and interact in complex patterns: TSH, T4 and T3:3  

  • Your pituitary gland produces TSH (thyroid stimulating hormone), which stimulates the thyroid gland to produce thyroid hormones.
  • Your thyroid gland then produces T4 (thyroxine) and T3 (triiodothyronine), which circulate in your bloodstream.
  • Your liver and kidneys convert T4 to T3 (triiodothyronine).
  • Your thyroid also produces other hormones important for bone metabolism.

T4 and T3 control your metabolism—your heart rate and the supply of energy to your cells and nervous system for activity, growth or body heat.

Iodine is one of the main building blocks of both T4 and T3. For optimal thyroid function, appropriate amounts of iodine must be available to the thyroid. Good food sources of iodine are listed at right. Learn more in our Iodine therapy summary.

Thyroid Disorders and Cancer Risk or Development

Disorders in thyroid hormones are associated with increased risk of some cancer types:4

Thyroid Disorder Influence on Cancer Risk or Development
Low TSH levels
Elevated TSH levels
  • Associated with greater progression-free survival in a small study of breast cancer patients
Higher free T4 levels (but not TSH levels) 
Hyperthyroidism (overactive thyroid)
  • Increased overall cancer risk
  • Increased risk of thyroid cancer
  • Increased cancer mortality and reduced five- and ten-year survival in some studies, while others have found no association
  • Subclinical and clinical hyperthyroidism increase the risk of several solid malignancies 
  • Associated with increased risk of colorectal cancer
Hypothyroidism (underactive thyroid)
Induced hypothyroidism (intentionally created by medical treatment) 
Thyroid autoimmunity
  • Some studies have shown increased prevalence of thyroid autoimmunity—in which the immune system attacks the thyroid gland—in some cancer types (breast, gastric and pancreatic cancers and myelodysplastic syndrome). However improved outcomes have also been seen for breast or kidney cancer patients. Other studies have found lower incidence of thyroid autoimmunity in breast cancer patients.

 

Non-thyroidal illness syndrome (NTIS), also called euthyroid sick syndrome, occurs when thyroid function test results are abnormal without thyroid illness. NTIS may be associated with greater mortality and shorter overall survival with small-cell and non-small-cell lung cancer, glioma and lymphoma.5

Hormone levels and interactions may also support cancer progression by dampening immune responses.6

Hormone Supplementation

Thyroid hormone supplementation is associated with decreased risk of colorectal cancer, although T3 supplementation may interfere with colon cancer drug treatments. T4 and T3 can also interfere with the activity of bortezomib, a key drug in treating multiple myeloma.

The body's ability to use thyroid hormones—its bioavailability—can affect cancer development and spread. TSH can deliver signals to cells only if it can hook up with its receptors. The thyrotopin receptor gene (TSH-R, Genetics Home Reference) turns these receptors on and off. If this receptor is turned off (not expressed), thyroid hormones cannot bind and deliver their messages. Increasing the amount of thyroid hormone with supplementation will not improve the hormone’s effects on cancer progression. This has been validated in cell studies: human breast cancer tissues without expression of the thyrotropin receptor had more progressed cancer—higher pathologic grades—than those with TSH-R expression.7

Possibilities for Treatments

Hormones may stimulate cell growth through various pathways.8 Reducing thyroid hormones with chemical treatment or inhibiting their ability to bind to receptors are possible treatment pathways needing more investigation.9

Written by Laura Pole, RN, MSN, OCNS, and reviewed by Nancy Hepp, MS, and Maria Williams; most recent update on May 22, 2020.

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