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Thyroid

This information should not be used for self-diagnosis or in place of a qualified physician's care.

Reviewed March 2016

The basics
  • Guidelines for treating this cancer have been developed by the Head and Neck Tumour Group.
  • For health professional information on treating this cancer, please see our Cancer Management Guidelines.
  • Thyroid cancer is also called thyroid carcinoma.
  • The thyroid gland is part of the endocrine system, and is located at the base of the throat, below the Adam's apple (voice box or larynx) and above the collar bones.
  • The thyroid is butterfly-shaped, with a lobe on each side of the windpipe (trachea) connected by a narrow band of tissue (the isthmus).
  • Each lobe is between 4 to 6 cm in length.
  • The thyroid uses iodine to produce hormones that regulate the body's metabolism. The thyroid hormones are thyroxine (T4) and triiodothyronine (T3).
  • Two parathyroid glands lie on the back surface of each lobe of the thyroid. These glands, together with C-cells in the thyroid, produce calcitonin which controls calcium levels in the body.

What causes it and who gets it?

Listed below are some of the known risk factors for this cancer. Not all of the risk factors below may cause this cancer, but they may be contributing factors.

  • Thyroid cancer is an uncommon cancer.
  • It occurs most often in those between 25 and 65 years of age.
  • Women are much more likely than men to develop thyroid cancer.
  • Excessive radiation exposure is a risk for thyroid cancer.
  • People who receive radiation treatment in infancy or early childhood have an increased risk of developing thyroid cancer in later life.
  • Imaging tests, X-rays and CT scans expose children to radiation, but it is uncertain whether these much lower doses raise the risk of thyroid cancer.
  • Having a close relative diagnosed with thyroid cancer may have increased risk.
  • People with chronically high TSH levels (thyroid-stimulating hormone) may have increased risk.
  • People with a goiter (a benign enlargement of the thyroid) or with a family history of goiter may have an increased risk of developing papillary thyroid cancer. 
  • Some rare hereditary medical conditions may increase the risk of thyroid cancer:
  • Statistics

Can I help to prevent it?

  • Including adequate amount of iodine in the diet may decrease the risk. North American diets usually have adequate iodine because it is added to table salt.

Screening for this cancer

  • No effective screening program exists for this cancer yet.
  • Some medullary thyroid cancers are hereditary. Patients with this type of cancer and their families may be screened by measuring the hormone calcitonin in the blood, and they may be referred to the Hereditary Cancer Program.

Signs and symptoms

  • Painless lump or swelling in the neck
  • Enlarged thyroid gland (goiter) - or collar getting tight
  • May present with lymph node metastasis
  • Late symptoms - due to local growth and spread to surrounding tissues may include:
    • Difficulty breathing and swallowing
    • Hoarseness
    • Metastasis to other sites
Diagnosis & staging

Diagnosis

These are tests that may be used to diagnose this type of cancer.

  • Thyroid cancers are often found during a regular physical check-up.
  • People with enlarged thyroid should have thyroid function blood tests and an ultrasound scan.
  • Fine needle aspiration biopsy (FNA) may provide the diagnosis.
  • A thyroid scan using a radioactive iodine tracer is sometimes helpful.
For more information tests used to diagnose cancer, see our Recommended Websites, Diagnostic Tests section.

Types and stages

Types
There are 4 main types of thyroid tumours, based on how the cancer cells look under a microscope: 

Papillary carcinoma
  • This is the most common form in Canada - over 80% of thyroid cancers diagnosed are papillary.
  • It is slow-growing. Patients have excellent survival if diagnosed early. 
  • It is usually found in only one of the lobes.
Follicular carcinoma
  • This is the second most common type of thyroid cancer.
  • It arises from follicular cells which are responsible for producing thyroid hormones.
  • It is slow-growing. Patients have excellent survival if diagnosed early.
  • It is often treated with radioactive iodine since this tumour is most likely to capture radioactive iodine.
Medullary carcinoma
  • It arises from C-cells which produce the hormone calcitonin.
  • It is slow-growing. Patients have good survival if diagnosed early.
  • It may spread to the lymph glands or to other sites in the body.
  • It usually only occurs on one side of the thyroid.
Anaplastic carcinoma
  • This is the least common type of thyroid cancer.
  • It occurs more often in middle aged and elderly people.
  • It is the most aggressive type of thyroid cancer. It is fast-growing with early spread.
  • It may be too advanced at the time of diagnosis to remove surgically.
  • It is often treated with radiation therapy alone.
  • This type of cancer is rarely cured.

Stages

Staging describes the extent of a cancer. The TNM classification system is used as the standard around the world. In general a lower number in each category means a better prognosis. The stage of the cancer is used to plan the treatment.
 

T describes the site and size of the main tumour (primary)

N describes involvement of lymph nodes

M relates to whether the cancer has spread (presence or absence of distant metastases)

Stage I
Confined to the thyroid

Stage II
Involving regional lymph nodes

Stage III
Locally invasive

Stage IV
Distant metastases

Treatment

Treatment

Cancer therapies can be highly individualized – your treatment may differ from what is described below.

Surgery
  • Surgery is the main type of treatment for thyroid cancers.
  • Surgical removal (thyroidectomy) is often all that is required.
  • The minimum operation is to remove the lobe where the cancer is. Removal of the isthmus and much of the other lobe may also be required.
  • More extensive surgery of the neck may be needed depending on the type and size of the tumour or whether the cancer has spread to lymph nodes.
  • Thyroid operations involve carefully preserving the parathyroid glands and the nerves that supply the larynx (voice box).
Radioactive Iodine Therapy
  • 131Iodine ablation may be used after surgery to destroy any remaining thyroid tissue where cancer may recur or to treat disease that has already recurred or metastasized (spread).
  • Only papillary and follicular cancers will take up iodine, and only 50% or less of these tumours are able to take up enough iodine to be therapeutic.
  • Before iodine therapy, the patient must stop taking thyroxine (T4) for at least 4 weeks and triiodothyronine (T3) for at least 2 weeks so that treatment will work.
  • Radioactive iodine is given as a drink, so a patient must to stay in hospital for a few days after a therapeutic dose to allow the radioactivity to fall to safe levels.
  • Radioactive iodine is used in more than one way to treat metastatic thyroid cancer:
    • First, a high dose of iodine is given to destroy normal thyroid tissue. The resulting state of hypothyroidism can promote the tumour to take up the iodine allowing it to be used as therapy.
    • Then, to test whether the metastatic tumour has taken up the iodine, before having a full-body scan, the patient swallows a small amount of radioactive iodine. This outpatient test is called a radioactive iodine scan or radionuclide scan.
  • Possible side effects of treatment include temporary bone marrow suppression (the bone marrow does not make normal levels of blood cells), inflammation of salivary glands, nausea and vomiting.
Radiotherapy
  • External beam radiation therapy is used after surgery and radioactive iodine therapy when there is a high risk of recurrence in the thyroid or neck. This may be because tissue has been left behind or because the tumour does not take up iodine.
  • Radiation therapy may also be used to treat tumours that cannot be removed surgically.
  • The course of treatment lasts between 4 and 7 weeks.
  • Side effects may include temporary reddening of skin, sore throat and laryngitis.
Chemotherapy
  • Chemotherapy plays a limited role in treatment, and is not meant to cure the thyroid cancer. 
  • Chemotherapy is used when the cancer cannot be controlled with radiotherapy.
Thyroxine Hormone Replacement
  • After treatment it is essential to take thyroxine hormone pills to replace what the thyroid would normally produce. Slightly higher doses than are necessary for replacement alone appear to reduce the risk of cancer recurring.

Follow-up after treatment

  • Guidelines for follow-up after treatment are covered on our website.
  • You will be returned to the care of your family doctor or specialist for regular follow-up. If you do not have a family physician, please discuss this with your BC Cancer Agency oncologist or nurse.
  • Follow-up testing is based on your type of cancer and your individual circumstances.
  • Life after Cancer focuses on the issues that cancer survivors can face.
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