Thyroid Carcinoma

Thyroid Carcinoma

The thyroid is an important endocrine gland located in the lower neck below the thyroid cartilage or Adam’s apple. Hormones produced by the thyroid gland (T3 and T4) mainly helps in regulating the metabolism of the body. Cancer in the thyroid gland is a malignant tumor originating from the tissue of this gland.


Epidemiology

Thyroid cancers are quite rare, accounting for only 1.5% of all cancers in adults and 3% of all cancers in children. The incidence of thyroid cancer is increasing and varies throughout the world. Most thyroid cancers diagnosed each year in the United States are of the papillary type which account for almost 75-85 % of thyroid cancer cases. Women are more prone to thyroid cancer than men.

The types of carcinoma in thyroid include the following:

  • Papillary carcinoma (75% to 85% of cases): It is the most common type, and usually affects women in their forties to fifties. It spreads slowly and is the least dangerous type of thyroid cancer.
  • Anaplastic carcinoma (also called giant and spindle cell cancer) (less than 5% cases): Although rare, it is the severest form of thyroid cancer. It spreads fast and hardly responds to radioiodine therapy. Anaplastic carcinomas do not express thyroid specific genes on their membrane. They do not produce thyroglobulin and TSH receptors are not found on their membrane.
  • Follicular carcinoma (10% to 20% of cases): Follicular thyroid carcinoma (FTC) is a well-differentiated tumor. It originates in follicular cells and is the second most common cancer of the thyroid, after papillary carcinoma. Thyroglobulin (Tg) can be used as a tumor marker for well-differentiated follicular thyroid carcinoma.  It is more likely to come back and spread than papillary carcinoma but still has a good prognosis. There is a subtype called oxyphil or Hurthle cell carcinoma that is harder to treat.
  • Medullary carcinoma (5% to 8% of cases): It is a cancer of non-thyroid cells in the thyroid gland. These cells are called “C” cells, which produce a hormone called calcitonin. Medullary carcinoma can be of two types: sporadic and inherited. Various mutations have been associated with medullary carcinoma. RET point mutations are linked with the development of medullary thyroid carcinomas. Treatment for this kind of cancer is different.

 

Risk factors and causes

Papillary carcinoma: These tumors are often caused due to high dose of radiation to the neck.

Anaplastic carcinoma: If a thyroid tumor exists for a long time it may be converted to anaplastic carcinoma due to prolonged stimulation with TSH. But, this frequency of transformation is rare.

Follicular carcinoma: These tumors are rarely caused due to high dose of radiation to the neck. A diet low in iodine is also a risk factor, although this is rare in the United States.

Medullary carcinoma: The cause of this cancer is not radiation. One fourth of medullary thyroid cancer is genetic in nature, caused by a mutation in the RET proto-oncogene.

There are other genetic syndromes that can include thyroid cancer.

Because of the risk of thyroid cancer following radiation accidents such as those involving nuclear power plants, people who live near reactors should have potassium iodide tablets to keep on hand. Should an accident occur, taking the potassium iodide protects the thyroid from the effects of radiation.

The general symptoms of all carcinomas in thyroid include:

  • Goiter (enlarged thyroid)
  • Lump in the neck in the area of the thyroid gland
  • Difficulty swallowing
  • Hoarseness or a change in the voice
  • Cough
  • Breathing problems due to narrowing of airways

Diagnosis

Physical exam: Lymph nodes in the neck may be swollen. Thyroid function tests are usually normal. However, an examination of the thyroid may reveal single or multiple nodules (lumps). One third of the patients with anaplastic carcinoma have had a goiter for a long time.

Other tests that may be used to diagnose carcinoma of the thyroid include:

Calcitonin blood test: This test measures the amount of calcitonin in the blood. Calcitonin is a hormone produced by special cells in the thyroid called C-cells. Excessive amounts of calcitonin are produced in medullary thyroid carcinoma.

CEA blood test: Elevated levels of CEA (carcinoembryonic antigen) may be detected in medullary carcinoma. The test is not specific for this cancer only.

TSH assay: Abnormal levels of TSH can also be detected in the blood during thyroid cancer.

Radioactive iodine scan (RAI scan): This test is conducted with radioactive iodine, which is normally taken up in less amounts by the cancer cells of thyroid than the normal cells. The camera is placed in front of the neck to measure the amount of radiation in the gland. Abnormal parts showing less radioactivity than the surrounding tissue are called cold nodules, and areas that take up more radiation are called hot nodules. Hot nodules usually are not cancerous, but cold nodules can be either benign or cancerous.

Laryngoscopy: A laryngoscope is used in this procedure to check the larynx (voice box). A laryngoscope is a thin, tube-like instrument with a light and a lens for viewing. A thyroid tumor may press on vocal cords. The laryngoscopy is done to check proper movements of the vocal cords.

Thyroid biopsy: It can be of two types: FNA biopsy (done by fine needle) and surgical biopsy (done after surgery). The tissues samples are then studied under a microscope. The type of carcinoma can be determined from this test.

Ultrasound and CT scan: These imaging techniques give a clear view of the affected region and detect thyroid cancer.

Treatment

Treatment depends on the type of thyroid cancer. Thyroid hormone must be taken after most treatments. If the thyroid is removed by surgery or destroyed by radiation, thyroid hormone must be replaced. Also, higher levels of thyroid taken by mouth turn down the production of a hormone called TSH by the pituitary. TSH stimulates thyroid tissue to produce thyroid hormone. Keeping TSH low reduces the chance of any left-over thyroid cells from growing or cancer from returning.

Surgery: It is the main treatment. Usually the thyroid gland is completely removed. In most cases of papillary carcinoma removal of the thyroid gland cures the patient. Medullary cancer requires complete thyroid removal plus a dissection to remove the lymph nodes of the front and sides of the neck. Anaplastic carcinoma patients may require a very aggressive surgery and tracheostomy during the treatment.

Radiation therapy: The radiation therapy can be given alone or after surgery. Radiation can be given in the form of an external beam of x-ray or in the form of radioiodine pills. Patients with papillary or follicular thyroid carcinoma can take radioactive iodine-131 for removal of residual thyroid tissue after surgery. This treatment does not improve the condition of patients with medullary and anaplastic cell carcinoma.

Chemotherapy: This mode of therapy is rarely effective for treating thyroid cancer. Doctors try chemotherapy only when the other modes of therapy fail to combat the disease allowing it to spread to other regions of the body.

New drugs like vandetanib, sorafenib and sunitinib may be used in the treatment of thyroid cancer as has been done recently in clinical trials. These drugs target receptors on thyroid cancer cells. They are more likely to be used in treating medullary thyroid cancer.

Prognosis – Five-year relative survival rates

Papillary carcinoma: They are usually slower growing. Most people are cured and have a normal life expectancy. The cure rate is 97 %. This form can be completely cured until stage III. The survival rate is around 51 % in stage IV.

Follicular carcinoma: They usually grow fast and may invade other tissues, but the prognosis is still good for this form of carcinoma. The cure rate is 97 %. The survival rate is 100 % in stage I and II. But, the rate decreases from 71% in stage III to 50% in stage IV.

Medullary carcinoma: The prognosis is worse than the previous ones. The outcome varies with age and other factors. The survival rate is good for the first 3 stages, but drastically less in Stage IV (28%).

Anaplastic carcinoma: It has a very poor prognosis and worst of all the types of thyroid cancer. It is normally detected at stage IV. It is usually fatal despite treatment.

References:

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  7. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.