Causes and Diagnoses

Causes and Diagnoses of Thyroid Cancer

The exact cause of thyroid cancer is unknown, but certain factors increase your risk of developing this type of cancer. Risk factors include:

  • Gender: Thyroid cancers are more common in women
  • Exposure to radiation: Prior history of radiation therapy
  • Diet: Low-iodine diet
  • Family history: Certain hereditary conditions can predispose to the development of thyroid cancer

A variety of genetic mutations have been found in thyroid cancer. The pattern is different in different types of thyroid cancer.


Diagnosis of thyroid cancer requires confirmation of the tissue type with a biopsy as well as additional tests, if indicated for assessing the extent of spread in the body.

The most common method of biopsy is with a test called fine needle aspiration, in which a thin needle is directed into the thyroid lump or nodule to obtain a small amount of material that can examined under the microscope. Frequently, an ultrasound is used to direct the needle precisely into the nodule. Sometimes additional testing may be necessary to look for specific mutations to clarify a result that was read as “suspicious” or “of undermined significance."

If the diagnosis is not fully clear from needle biopsy, a diagnostic removal of a lobe (one half) of the thyroid gland may be performed as a first step. If malignancy is confirmed, additional considerations are applied to determine if a completion thyroidectomy (removal of the remaining thyroid gland) will be necessary.

Following removal of the gland for thyroid cancer, many patients will require treatment with radioactive iodine. A whole body scan is performed after this treatment to look for spread of cancer outside the neck.

A CT scan or an MRI scan may occasionally be ordered if there is suspicion of invasion or compression of the airway (voice box and wind pipe) by the cancer. A PET scan is sometimes necessary if they the thyroid cancer is of a kind that does not take up iodine.

Related Resources

Useful Links
Thyroid Cancer Treatment

Thyroid Ultrasound Brochure
: Learn about the preparations and care needed before and after this procedure. English | Spanish