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Thyroid Cancer

What is the thyroid and what does it do?

The thyroid gland is a butterfly-shaped organ which is wrapped around the windpipe and is located at the base of the neck, just below the voice box, or larynx.1 The thyroid gland’s function is the production, storage and release of thyroid hormones into your bloodstream. Thyroid hormones act throughout the body, influencing metabolism, growth and development, and body temperature.1,2 The main hormones are thyroxine (T4) and triiodothyronine (T3).2

thyroid gland

Figure 1: Thyroid Gland (2009 WebMD, https://images.app.goo.gl/a6Ri7LEU4CwJQiap7)

What is thyroid cancer?

Thyroid cancer occurs when a cancerous tumour is found in the thyroid gland. Cancer begins in cells when cell growth is abnormal, and which then leads to abnormal tissue formation. The abnormal tissue in the thyroid gland is referred to as a nodule which then can develop into either a benign nodule or a cancerous tumour. Most thyroid nodules are benign. Benign nodules are not cancer (malignant).1

Incidence of thyroid cancer in South Africa

According to the Cancer Association of South Africa (CANSA), about 50% of people over the age of 40 have a thyroid nodule, most of which are benign. Only 7-15% of thyroid nodules are malignant.1 Thyroid cancer is usually very treatable, even if at a more advanced stage. Effective treatments and surgery could provide a full recovery and/or cure .3

The estimated burden of thyroid cancer for South Africa for 2018 (based on Globocan estimates):4

  • Annual number of thyroid cancer cases 2408
  • Annual number of thyroid cancer deaths 157

Signs and Symptoms of Thyroid Cancer

There are signs and symptoms which, although they aren’t necessarily always associated with thyroid cancer, should be evaluated by a doctor:

  • A lump in the neck
  • Swollen lymph nodes
  • Hoarse voice.
  • Difficulty swallowing or breathing.
  • Neck or throat pain1

Treatment

Thyroid cancer treatment options depend on the type and stage of the thyroid cancer, the overall health of the patient and his/her preferences. Most cases of thyroid cancer can be cured with treatment.1

Surgical treatment

Surgery to remove the entire thyroid (thyroidectomy) is the most common treatment for thyroid cancer. Enlarged lymph nodes from the neck may also be surgically removed and tested for cancer cells.1

Thyroid hormone treatment1

Thyroid hormone medication is prescribed after surgery in order to replace the T4 that was produced by the thyroid. Thyroid hormone treatment will also prevent the overproduction of thyroid stimulating hormone (TSH) by the pituitary gland, which is important, as higher TSH levels may cause any existing cancer cells to grow. Thyroid hormone levels should be monitored every few months to ensure correct dosing.

Radioactive iodine therapy (RAI)1

RAI therapy is available in a capsule or liquid and is taken up primarily by thyroid cells and thyroid cancer cells, so the risk of harming other cells in the body is low.

Follow-up testing after treatment

Although thyroid cancer patients generally have a long survival, they also have relatively high rates of tumour recurrence (10-30%). Therefore, timely detection and treatment of recurrent tumours is important to decrease morbidity and mortality associated with such disease.5

Long-term follow-up monitoring is vital after thyroid cancer treatment. The following tests are recommended:

Thyroglobulin testing

Thyroglobulin is a protein produced by thyroid cells (both normal and cancerous cells). After removal of the thyroid gland, Thyroglobulin can be used as a "cancer marker." Its number should be as low as possible. Sometimes this is termed "undetectable.”6 Tg testing is recommended to be done every 6 months post-treatment.7

Neck ultrasound

This test is used to detect potential disease in the neck with no radiation exposure associated with it.6 Recommended that this be done every 6-12 months after surgery.7

Whole body scan

This is generally a “stimulated” scan, with your TSH elevated. Therefore, it will be done either after thyroid hormone withdrawal (you stop taking your pills for a period of time). This will raise the level of thyroid stimulating hormone (TSH) and the RAI will be absorbed by the remaining thyroid cancer cells, where it will accumulate.6 Recommended to be done 6-12 months after RAI treatment.7

For both ablation and whole-body scan, hormonal withdrawal is crucial to ensure that remnant thyroid cells take up the RAI. Patients experience hypothyroid symptoms during thyroid hormone discontinuation that include depression, inability to concentrate/think and fatigue.8

thyroid awareness

REFERENCES:

  1. Herbst MC, CANSA Fact sheet on cancer of the thyroid; 2017 [cited 2020 Feb 28]; http://www.cansa.org.za/files/2017/05/Fact-Sheet-Cancer-of-Thyroid-NCR-2012-web-May-2017.pdf 2017; 1: 1-26
  2. British Thyroid Foundation [Internet]. Harrogate, United Kingdom: BTF. Your thyroid gland; [cited 2020 Feb 28]. Available from: http://www.btf-thyroid.org/information/your-thyroid-gland
  3. WebMD. What Is Thyroid Cancer? 2017. (cited 2020 Mar 04); Available from: https://www.webmd.com/cancer/what-is-thyroid-cancer#2
  4. Cancer Association of South Africa [Internet]. Johannesburg, South Africa: CANSA; c2020. Fact sheet on cancer of the thyroid; 2020 [cited 2020 Feb 28]; Available from: https://www.cansa.org.za/files/2020/02/Fact-Sheet-on-Cancer-of-the-Thyroid-NCR-2014-web-February-2020.pdf
  5. Luster M. Present status of the use of recombinant human TSH in thyroid cancer management. Acta Oncologica 2006; 45:1018-1030.
  6. Thyroid Cancer Survivors' Association, Inc. Follow-Up Testing. 2013. (Cited 2020 Mar 4) Available from: www.thyca.org/pap-fol/follow-up-testing/
  7. Haugen BR, Alexander K, Bible KC, et al. 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2016;26(1):1-133.
  8. Banach R, Bartès B, Farnell K, et al. Results of the Thyroid Cancer Alliance international patient/survivor survey: Psychosocial/informational support needs, treatment side effects and international differences in care. Hormones 2013;12(3):428-438.