Head & Neck

Thyroid Cancer

Cancer of the thyroid gland is an abnormal growth of cells in the butterfly-shaped gland located at the base of the neck (see figure below). The thyroid gland produces hormones that control heart rate, body temperature and metabolism (how quickly food is changed into energy). The thyroid also partially controls the amount of calcium in the blood.

A variety of nodules may develop in the thyroid, some cancerous (malignant), others noncancerous (benign). The primary types of thyroid cancer include papillary carcinoma (the most common), follicular carcinoma, medullary thyroid carcinoma and anaplastic carcinoma. Though its rare, lymphoma can also occur in the thyroid. Cancerous tumors can spread (metastasize) into nearby tissues and organs or to other parts of the body if left untreated.

Diagnosing thyroid cancer

Your doctor may suspect thyroid cancer if he or she feels any lumps or swelling in the neck or lymph nodes in the neck. One or more of the following tests may be ordered if thyroid cancer is suspected:

  • Laryngoscopy is a procedure in which the doctor checks the larynx (voice box) with a mirror or with a laryngoscope. The laryngoscopy is done to see if the vocal cords are moving normally.
  • Blood hormone studies measure the amounts of certain hormones released into the blood by organs and tissues in the body. A higher than normal amount of a substance can be a sign of disease in the organ or tissue that makes it.
  • Blood chemistry studies measure the amounts of certain substances, such as calcium, released into the blood by organs and tissues in the body. An unusually high or low amount of a substance can be a sign of disease.
  • Ultrasound is a procedure that forms a picture of body tissues called a sonogram. This procedure can show the size of a thyroid nodule and whether it is solid or a fluid-filled cyst. Ultrasound may be used to guide a fine-needle aspiration biopsy.
  • Thyroid radioiodine scan involves a small amount of radioactive iodine being swallowed. Several hours later, a camera is placed in front of the neck to measure the amount of radiation that has absorbed in the gland and to see where areas of radioactivity may be. This test is not used for medullary thyroid cancer because this type of cancer cell does not absorb iodine.
  • Computed tomography (CT) is a test that involves a scanner linked to a computer that makes a series of detailed cross-sectional images, taken from different angles, of areas inside the body. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly.
  • Fine-needle aspiration biopsy is the removal of thyroid tissue with use of a thin needle. A pathologist views the tissue samples under a microscope to look for cancer cells.
  • Surgical biopsy is the removal of one lobe of the thyroid during surgery so the cells and tissues can be viewed under a microscope by a pathologist to check for signs of cancer.

The risk factors for this cancer include a family or personal history of thyroid cancer or goiter (a noncancerous swelling of the thyroid gland) and some inherited genetic conditions, such as familial medullary carcinoma, familial adenomatous polyposis, Lynch syndrome and multiple endocrine neoplasia. Some types of thyroiditis can also lead to thyroid cancer.

Staging

Staging is how physicians determine the extent of your cancer, where it is located, and whether it has metastasized to nearby organs or tissue or to other parts of your body.

The TNM staging system, developed by the American Joint Committee on Cancer (AJCC), is typically used to stage head and neck cancers. This system classifies the cancer by tumor (T), node (N) and metastasis (M). The T category describes the size and location of the primary tumor. The N category describes lymph node involvement, indicating whether the lymph nodes show evidence of cancer cells. The location of these lymph nodes is important because it shows how far the disease has spread. The pathologic N category (sometimes denoted as pN) describes how many lymph nodes are involved and the amount of tumor cells found in the nodes. The M category describes distant metastasis (spread of cancer to another part of the body), if any. Staging for the M category is mainly clinical; however, a new M subcategory may be given based on the presence of tumor cells that can only be detected using a microscope or molecular testing.

Once the cancer has been classified, an overall stage is assigned. The main stages are Stage 0 (or I) through Stage IV, where Stage 0 (also known as “in situ”) is a precursor of an invasive cancer. Stages I and II are confined to the local area where the cancer is found; Stage III has often spread to the regional lymph nodes or lymphatic channels; and Stage IV has spread to distant sites (such as the lung or bone). Even these basic stages are sometimes further divided into subgroups of tumors that have a similar prognosis (Stage IB, Stage IIIC, etc). This grouping allows doctors to more accurately predict survival outcome according to stage and to adjust the treatment to the stage or substage of the cancer. For certain cancers, the AJCC also recommends tumor genetic testing, which can help determine which treatments are likely to be most effective.

For thyroid cancer, the TNM classification relates to specific stages depending on the specific type of thyroid cancer. Medullary thyroid cancer is staged from stage I to stage IVC. In papillary and follicular thyroid cancers, age is a factor in staging. Disease in people younger than 45 years is diagnosed as either Stage I or II. Disease in people 45 years or older can be staged from Stage I to IVC. All anaplastic cancers are classified as Stage IV and range from Stage IVA to IVC.

Although the original stage at diagnosis does not change, a doctor may reassess an individual’s cancer after treatment or if it has recurred, in a process known as restaging. This is rarely done but will likely involve the same diagnostic tests used for the original diagnosis. If a new stage is assigned, it’s often preceded by an “r” to denote that it’s a restage and different from the original stage given at diagnosis.

TNM classification for thyroid cancer

Classification Definition
Tumor (T)
Tx Primary tumor cannot be assessed.
T0 No evidence of primary tumor.
T1
  T1a
  T1b
Tumor is 2 centimeters (cm) (about ¾ inch) or less in diameter and is limited to the thyroid.
Tumor is 1 cm or less, limited to the thyroid.
Tumor is more than 1 cm but not more than 2 cm in diameter, limited to the thyroid.
T2 Tumor is more than 2 cm but not more than 4 cm in greatest dimension and is limited to the thyroid.
T3 Tumor is more than 4 cm in diameter and is limited to the thyroid or any tumor with minimal extrathyroid extension (e.g., extension to sternothyroid muscle or perithyroid soft tissue).
T4a Moderately advanced disease. Tumor of any size that extends beyond the thyroid capsule to invade subcutaneous soft tissues, larynx (voice box), trachea (windpipe), esophagus or recurrent laryngeal nerve.
T4b Very advanced disease. Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels.
Node (N)
Nx Regional lymph nodes cannot be assessed.
N0 No regional lymph node metastasis.
N1
  N1a
  N1b
Metastasis to regional lymph nodes.
Metastasis to lymph nodes in the pretracheal, paratracheal and prelaryngeal/Delphian areas.
Metastasis to unilateral, bilateral or contralateral cervical lymph nodes on one or both sides or to retropharyngeal or superior mediastinal lymph nodes.
Metastasis (M)
M0 No distant metastasis, has not spread to distant organs.
M1 Distant metastasis, has spread to distant organs.

 

Stages of anaplastic thyroid cancer*

Stage T N M
IVA T4a Any N M0
IVB T4b Any N M0
IVC Any T Any N M1
*All anaplastic carcinomas are classified as T4 tumors.
Anaplastic carcinoma is classified as T4 when it is
limited to the thyroid and as T4b when it extends
beyond the thyroid.

 

Stages of medullary thyroid cancer*

Stage T N M
I T1 N0 M0
II T2 to T3 N0 M0
III T1 to T3 N1a M0
IVA T4a
T1 to T3
Any N
N1b
M0
M0
IVB T4b Any N M0
IVC Any T Any N M1

 

Stages of papillary or follicular thyroid cancer*

Stage T N M
I Any T Any N M0
II Any T Any N M1
*In people younger than 45 years old

 

Stages of papillary or follicular thyroid cancer*

Stage T N M
I T1 N0 M0
II T2 N0 M0
III T3
T1 to T3
N0, N1a
N1b
M0
M0
IVA T4a
T1 to T4a
N0, N1a
N1b
M0
M0
IVB T4b Any N M0
IVC Any T Any N M1
*In people 45 years and older

 

Treatment options

The most common treatment options for thyroid cancer are surgery and radiation therapy. Other treatments include chemotherapy and immunotherapy.

Surgery

Surgery to remove all or most of the thyroid gland is the most common treatment for thyroid cancer. In addition to removing the thyroid, your surgeon may also remove lymph nodes in the neck to see if the cancer has metastasized. In certain low-risk patients, a hemithyroidectomy may be performed in which only half of the thyroid is removed. In addition, thyroid hormone therapy or oral radioactive iodine treatment, or both, may be given after surgery.

Radiation therapy

Radiation therapy is often recommended if the cancer has spread to the bones and as a follow up to surgery in the event there are areas of cancer that could not be reached surgically. It is also used in patients who may have a recurrence of cancer. With this type of treatment, known as external-beam radiation therapy, a machine delivers high-energy beams of radiation, usually X-rays or gamma rays, at specific points of the body to destroy cancer cells. Radiation therapy is usually given for about six weeks, once a day for 15 to 30 minutes, five days a week.

Radioactive iodine (radioiodine) therapy

This treatment involves swallowing radioactive iodine (RAI) which will then concentrate in the thyroid cells because the thyroid gland absorbs nearly all of a body’s iodine. This treatment can be used to destroy any thyroid tissue left after surgery or to treat some types of thyroid cancer that have spread to lymph nodes and/or other parts of the body. (The dose of RAI is much higher than what is used in a thyroid scan.)

Chemotherapy

If surgery and radiation therapy are not successful, chemotherapy may be used to treat thyroid cancer. Alone or in combination with two or more drugs, chemotherapy is a systemic therapy that works by killing cancer cells or stopping them from growing and spreading.

Immunotherapy

Immunotherapy uses the body’s own immune system to slow and kill cancer cells. With this treatment approach, substances — made either by the body or in a laboratory — are used to identify cancer cells as a threat and target them for destruction.

 

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