After thyroid cancer has been diagnosed, tests are done to find out if cancer cells have spread within the thyroid or to other parts of the body.

The process used to find out if cancer has spread within the thyroid or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests and procedures may be used in the staging process:

• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.

• Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram. The picture can be printed to be looked at later.

• Chest x-ray : An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.

• Sentinel lymph node biopsy : The removal of the sentinel lymph node during surgery. The sentinel lymph node is the first lymph node to receive lymphatic drainage from a tumor. It is the first lymph node the cancer is likely to spread to from the tumor. A radioactive substance and/or blue dye is injected near the tumor. The substance or dye flows through the lymph ducts to the lymph nodes. The first lymph node to receive the substance or dye is removed. A pathologist views the tissue under a microscope to look for cancer cells. If cancer cells are not found, it may not be necessary to remove more lymph nodes.

There are three ways that cancer spreads in the body.

The three ways that cancer spreads in the body are:

• Through tissue. Cancer invades the surrounding normal tissue.
• Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
• Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.

When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.

The following stages are used for papillary and follicular thyroid cancer in patients younger than 45 years:

Stage I

In stage I papillary and follicular thyroid cancer, the tumor is any size, may be in the thyroid, or may have spread to nearby tissues and lymph nodes. Cancer has not spread to other parts of the body.

Stage II

In stage II papillary and follicular thyroid cancer, the tumor is any size and cancer has spread from the thyroid to other parts of the body, such as the lungs or bone, and may have spread to lymph nodes.

The following stages are used for papillary and follicular thyroid cancer in patients 45 years and older:

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Pea, peanut, walnut, and lime show tumor sizes.

Stage I

In stage I papillary and follicular thyroid cancer, cancer is found only in the thyroid and the tumor is 2 centimeters or smaller.

Stage II

In stage II papillary and follicular thyroid cancer, cancer is only in the thyroid and the tumor is larger than 2 centimeters but not larger than 4 centimeters.

Stage III

In stage III papillary and follicular thyroid cancer, either of the following is found:

• the tumor is larger than 4 centimeters and only in the thyroid or the tumor is any size and cancer has spread to tissues just outside the thyroid, but not to lymph nodes; or
• the tumor is any size and cancer may have spread to tissues just outside the thyroid and has spread to lymph nodes near the trachea or the larynx (voice box).

Stage IV

Stage IV papillary and follicular thyroid cancer is divided into stages IVA, IVB, and IVC.

• In stage IVA, either of the following is found:
  • the tumor is any size and cancer has spread outside the thyroid to tissues under the skin, the trachea, the esophagus, the larynx (voice box), and/or the recurrent laryngeal nerve (a nerve with two branches that go to the larynx); cancer may have spread to nearby lymph nodes; or
  • the tumor is any size and cancer may have spread to tissues just outside the thyroid. Cancer has spread to lymph nodes on one or both sides of the neck or between the lungs.
• In stage IVB, cancer has spread to tissue in front of the spinal column or has surrounded the carotid artery or the blood vessels in the area between the lungs; cancer may have spread to lymph nodes.
• In stage IVC, the tumor is any size and cancer has spread to other parts of the body, such as the lungs and bones, and may have spread to lymph nodes.

The following stages are used for medullary thyroid cancer:

Stage 0

Stage 0 medullary thyroid cancer is found only with a special screening test. No tumor can be found in the thyroid.

Stage I

Stage I medullary thyroid cancer is found only in the thyroid and is 2 centimeters or smaller.

Stage II

In stage II medullary thyroid cancer, either of the following is found:

• the tumor is larger than 2 centimeters and only in the thyroid; or
• the tumor is any size and has spread to tissues just outside the thyroid, but not to lymph nodes.

Stage III

In stage III medullary thyroid cancer, the tumor is any size, has spread to lymph nodes near the trachea and the larynx (voice box), and may have spread to tissues just outside the thyroid.

Stage IV

Stage IV medullary thyroid cancer is divided into stages IVA, IVB, and IVC.

• In stage IVA, either of the following is found:
  • the tumor is any size and cancer has spread outside the thyroid to tissues under the skin, the trachea, the esophagus, the larynx (voice box), and/or the recurrent laryngeal nerve (a nerve with 2 branches that go to the larynx); cancer may have spread to lymph nodes near the trachea or the larynx; or
  • the tumor is any size and cancer may have spread to tissues just outside the thyroid. Cancer has spread to lymph nodes on one or both sides of the neck or between the lungs.
• In stage IVB, cancer has spread to tissue in front of the spinal column or has surrounded the carotid artery or the blood vessels in the area between the lungs. Cancer may have spread to lymph nodes.
• In stage IVC, the tumor is any size and cancer has spread to other parts of the body, such as the lungs and bones, and may have spread to lymph nodes.

Anaplastic thyroid cancer is considered stage IV thyroid cancer.

Anaplastic thyroid cancer grows quickly and has usually spread within the neck when it is found. Stage IV anaplastic thyroid cancer is divided into stages IVA, IVB, and IVC.

• In stage IVA, cancer is found in the thyroid and may have spread to lymph nodes.
• In stage IVB, cancer has spread to tissue just outside the thyroid and may have spread to lymph nodes.
• In stage IVC, cancer has spread to other parts of the body, such as the lungs and bones, and may have spread to lymph nodes.