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Thyroid Cancer

Anatomical facts:

The thyroid is a gland that lies at the front of the neck, beneath the voice box (larynx). It has two lobes and is shaped like a butterfly. The thyroid produces a hormone that regulates the body’s metabolism. In order to produce thyroid hormone, the thyroid gland absorbs iodine from the blood.

Facts about the thyroid:

Thyroid nodules, which are benign tumors that develop on the thyroid gland, are very common and occur in one-third of all adults. Only 10% to 15% of these nodules are cancerous. About 33,000 new cases of thyroid cancer are diagnosed each year in the United States. Thyroid cancer may occur in people of all ages; however, most cases are discovered in women.
Most thyroid cancers can be successfully treated and cured. The number of deaths per year is approximately 1,500.

Risk factors:

Several risk factors for thyroid cancer have been identified A number of inherited syndromes increase the risk to develop thyroid cancer. Low iodine in the diet increases the incidence of follicular carcinomas. People who were exposed to radiation in the head and neck area, or were exposed to radioactive fallout from nuclear weapons or power plant accidents, also have a
higher risk.

Types:

Thyroid cancers are divided into a number of main types, and these are divided further into subtypes. There are significant differences in the natural history, treatment principles, and prognosis between these types. For this reason, it is important to find out the specific type the patient is inquiring about. A number of information sources offer separate sections for the specific types of thyroid cancer.

  • Papillary or follicular carcinomas: Eighty to ninety percent of thyroid cancers are papillary carcinomas or follicular carcinomas. (Subtypes of papillary carcinomas include the follicular variant, tall cell variant, columnar cell variant, and diffuse sclerosing variant.) Most of these tumors tend to grow slowly and can be treated successfully. One subtype of follicular carcinoma carries a worse prognosis.
  • Medullary thyroid carcinomas: Five to ten percent of thyroid cancers are medullary thyroid carcinomas (MTCs). These tumors have a worse prognosis than papillary and follicular carcinomas. About 20% of MTCs are inherited and run in families.
  • Anaplastic carcinoma: the rarest type of thyroid cancer, anaplastic carcinoma, is an aggressive
    cancer that spreads quickly to the neck and other parts of the body. Fortunately, less than 2% of thyroid cancers are of the anaplastic type.

Treatment:

Most thyroid cancer patients are treated with surgery to remove the tumor. Thyroidectomy is the name of the surgical procedure used to remove the entire thyroid. Sometimes it is possible to remove only one lobe of the thyroid. If the cancer has spread to nearby tissues, more neck tissue and lymph nodes will be removed. People who have had their thyroid removed will have to take thyroid hormone replacement pills for the rest of their life.

Cure rates for thyroid cancer are very high, and the great majority of patients can expect full recovery and high quality of life after treatment. Although they have to take thyroid hormone replacement pills for the rest of their lives, this therapy has very few side effects.

Total thyroidectomy: It refers to the removal of the thyroid.It is the most widely used treatment for thyroid cancer.

Near total thyroidectomy: It refers to almost complete removal of the thyroid. Surgeons leave out small portions of thyroidto avoid damage to the parathyroid gland.

Lymphadenectomy: It refers to the surgical removal of the lymph nodes in the neck region. Detection of cancer in the lymph nodes indicates spread of cancer cells from the thyroid to other tissues.

Lobectomy: It refers to the removal of a lobe of the thyroid which bears the cancer. After the surgery,  adjuvant therapy is required to prevent recurrence of the cancer.

Surgical removal of thyroid can be done by making an incision in the neck. The surgery can cause bleeding and infection, damage to parathyroid glands leading to low calcium levels, and damage to nerves connected to vocal cords that can cause vocal cord paralysis, hoarseness, soft voice or difficulty breathing.

Radioactive iodine therapy
Radioactive iodine treatment refers to the use of radioactive iodine (I-131) to kill cancer cells in the thyroid.  A low dose of I-131 is administered by mouth, which is absorbed in the intestine. The iodine is normally taken up by thyroid cells in the body. So the chances of killing normal cells are low. Thyroid cells of the thyroid gland and those that have metastasized will be killed by the effect of radiation from the I-131. This treatment is mostly conducted after surgery. It reduces the chance of recurrence of cancer. Radioactive I-131 is not used for patients with papillary cancer since they remain unaffected by this treatment. It is mostly recommended for patients with papillary and follicular forms of thyroid cancer.

Most of the I-131 leaves the body with the urine within a few days after treatment is completed. Nausea, dryness of skin and mouth, change in taste and sensation are some of the side effects.

External radiation therapy
External radiation therapy refers to the use of a machine which emits a beam of high energy aiming at the affected site in the body. It is usually given only for a few minutes for 5 days every week. This procedure is repeated for about six weeks. This form of treatment is normally used at  advanced stages of the disease.

Thyroid hormone therapy
Thyroid hormone therapy aims to replace the function of the thyroid gland after surgical removal or radioactive iodine treatment. It is mainly recommended for follicular and papillary cancer. The patient has to take thyroid hormone in the form of medicine for the rest of life. Levothyroxine, synthetic thyroid hormone, is used for this purpose.   The medicine not only supplies the thyroid hormone, but also prevents the production of thyroid stimulating hormone (TSH). Lowering the TSH hormone level is required to prevent the growth of cancer cells of the thyroid.

Chemotherapy

Chemotherapy is the use of drugs for the treatment of cancer. When drugs are administered through a vein or by mouth, then this kind of chemotherapy is called systemic chemotherapy. Direct administration of drugs to the affected region is called regional chemotherapy.
Chemotherapy is not usually recommended for the treatment of thyroid cancer. It may be used when other forms of treatment do not work or sometimes in combination with radiation therapy for the treatment of anaplastic thyroid cancer. Some of the chemotherapy drugs that may be used in such cases include doxorubicin, bleomycin, 5-FU, cisplatin, vincristine, cyclophosphamide and etoposide.

Targeted therapy

Targeted therapy refers to the use of drugs that specifically kills only cancer cells without damaging normal cells. There are different types of targeted therapy for the treatment of thyroid cancer, but most of them are in clinical trials.

New forms of targeted therapies are currently being studied. Drugs that inhibit the formation of blood vessels have entered clinical trials very recently for the treatment of metastatic thyroid cancer. Drugs targeting the VEGF receptors have been most successful. Kinases associated with the papillary and medullary thyroid cancers are also important drug targets.

Recently, two well know targeted therapy drugs, sorafenib and sunitinib, have shown some success in thyroid cancer treatment. Patients with advanced medullary cancer treated with the tyrosine kinase inhibitor, vandetanib in clinical trials showed improvement. Other new drugs are also in clinical trials.

Clinical trials
Clinical trials refer to those kinds of treatment which are not yet standardized. It is a part of research that aims to develop better strategies for the treatment of cancer. The patients may willingly participate in clinical trials, but cure is not guaranteed.

References:

Deshpande HA, Gettinger SN, Sosa JA. Targeted therapy for thyroid cancer: An updated review of investigational agents. Curr Opin Investig Drugs. 2010 Jun; 11(6):661-8.

Cox AE, LeBeau SO. Diagnosis and treatment of differentiated thyroid carcinoma. Radiol Clin North Am. 2011 May; 49(3):453-62, vi.

Milan SA, Sosa JA, Roman SA. Current management of medullary thyroid cancer. Minerva Chir. 2010 Feb; 65(1):27-37.

This article was originally published on 7/12/2014 and last revision and update of it was 9/14/2015.