Thyroid Cancer

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Early Detection, Diagnosis, and Staging TOPICS

How is thyroid cancer staged?

Staging is the process of finding out if and how far a cancer has spread. The stage of a cancer is one of the most important factors in choosing treatment options and predicting your chance for cure.

Staging is based on the results of the physical exam, biopsy, and imaging tests (ultrasound, radioiodine scan, CT scan, MRI, chest x-ray, and/or PET scans), which are described in the section “How is thyroid cancer diagnosed?

The TNM staging system

A staging system is a standard way to sum up how large a cancer is and how far it has spread.

The most common system used to describe the stages of thyroid cancer is the American Joint Committee on Cancer (AJCC) TNM system. The TNM system is based on 3 key pieces of information:

  • T indicates the size of the main (primary) tumor and whether it has grown into nearby areas.
  • N describes the extent of spread to nearby (regional) lymph nodes. Lymph nodes are bean-shaped collections of immune system cells to which cancers often spread first. Cells from thyroid cancers can travel to lymph nodes in the neck and chest areas.
  • M indicates whether the cancer has spread (metastasized) to other organs of the body. (The most common sites of spread of thyroid cancer are the lungs, the liver, and bones.)

Numbers or letters appear after T, N, and M to provide more details about each of these factors. The numbers 0 through 4 indicate increasing severity. The letter X means a category can’t be assessed because the information is not available.

T categories for thyroid cancer (other than anaplastic thyroid cancer)

TX: Primary tumor cannot be assessed.

T0: No evidence of primary tumor.

T1: The tumor is 2 cm (slightly less than an inch) across or smaller and has not grown out of the thyroid.

  • T1a: The tumor is 1 cm (less than half an inch) across or smaller and has not grown outside the thyroid.
  • T1b: The tumor is larger than 1 cm but not larger than 2 cm across and has not grown outside of the thyroid.

T2: The tumor is more than 2 cm but not larger than 4 cm (slightly less than 2 inches) across and has not grown out of the thyroid.

T3: The tumor is larger than 4 cm across, or it has just begun to grow into nearby tissues outside the thyroid.

T4a: The tumor is any size and has grown extensively beyond the thyroid gland into nearby tissues of the neck, such as the larynx (voice box), trachea (windpipe), esophagus (tube connecting the throat to the stomach), or the nerve to the larynx. This is also called moderately advanced disease.

T4b: The tumor is any size and has grown either back toward the spine or into nearby large blood vessels. This is also called very advanced disease.

T categories for anaplastic thyroid cancer

All anaplastic thyroid cancers are considered T4 tumors at the time of diagnosis.

T4a: The tumor is still within the thyroid.

T4b: The tumor has grown outside the thyroid.

N categories for thyroid cancer

NX: Regional (nearby) lymph nodes cannot be assessed.

N0: The cancer has not spread to nearby lymph nodes.

N1: The cancer has spread to nearby lymph nodes.

  • N1a: The cancer has spread to lymph nodes around the thyroid in the neck (called pretracheal, paratracheal, and prelaryngeal lymph nodes).
  • N1b: The cancer has spread to other lymph nodes in the neck (called cervical) or to lymph nodes behind the throat (retropharyngeal) or in the upper chest (superior mediastinal).

M categories for thyroid cancer

MX: Distant metastasis cannot be assessed.

M0: There is no distant metastasis.

M1: The cancer has spread to other parts of the body, such as distant lymph nodes, internal organs, bones, etc.

Stage grouping

Once the values for T, N, and M are determined, they are combined into stages, expressed as a Roman numeral from I through IV. Sometimes letters are used to further divide a stage. Unlike most other cancers, thyroid cancers are grouped into stages in a way that also considers the subtype of cancer and the patient’s age.

Papillary or follicular (differentiated) thyroid cancer in patients younger than 45

Younger people have a low likelihood of dying from differentiated (papillary or follicular) thyroid cancer. The TNM stage groupings for these cancers take this fact into account. So, all people younger than 45 years with these cancers are stage I if they have no distant spread and stage II if they have distant spread.

Stage I (any T, any N, M0): The tumor can be any size (any T) and may or may not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

Stage II (any T, any N, M1): The tumor can be any size (any T) and may or may not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Papillary or follicular (differentiated) thyroid cancer in patients 45 years and older

Stage I (T1, N0, M0): The tumor is 2 cm or less across and has not grown outside the thyroid (T1). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage II (T2, N0, M0): The tumor is more than 2 cm but not larger than 4 cm across and has not grown outside the thyroid (T2). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage III: One of the following applies:

T3, N0, M0: The tumor is larger than 4 cm across or has grown slightly outside the thyroid (T3), but it has not spread to nearby lymph nodes (N0) or distant sites (M0).

T1 to T3, N1a, M0: The tumor is any size and may have grown slightly outside the thyroid (T1 to T3). It has spread to lymph nodes around the thyroid in the neck (N1a) but not to other lymph nodes or to distant sites (M0).

Stage IVA: One of the following applies:

T4a, any N, M0: The tumor is any size and has grown beyond the thyroid gland and into nearby tissues of the neck (T4a). It might or might not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

T1 to T3, N1b, M0: The tumor is any size and might have grown slightly outside the thyroid gland (T1 to T3). It has spread to certain lymph nodes in the neck (cervical nodes) or to lymph nodes in the upper chest (superior mediastinal nodes) or behind the throat (retropharyngeal nodes) (N1b), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back toward the spine or into nearby large blood vessels (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor is any size and might or might not have grown outside the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Medullary thyroid cancer

Age is not a factor in the stage of medullary thyroid cancer.

Stage I (T1, N0, M0): The tumor is 2 cm or less across and has not grown outside the thyroid (T1). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage II: One of the following applies:

T2, N0, M0: The tumor is more than 2 cm but is not larger than 4 cm across and has not grown outside the thyroid (T2). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

T3, N0, M0: The tumor is larger than 4 cm or has grown slightly outside the thyroid (T3), but it has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage III (T1 to T3, N1a, M0): The tumor is any size and might have grown slightly outside the thyroid (T1 to T3). It has spread to lymph nodes around the thyroid in the neck (N1a) but not to other lymph nodes or to distant sites (M0).

Stage IVA: One of the following applies:

T4a, any N, M0: The tumor is any size and has grown beyond the thyroid gland and into nearby tissues of the neck (T4a). It might or might not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

T1 to T3, N1b, M0: The tumor is any size and might have grown slightly outside the thyroid gland (T1 to T3). It has spread to certain lymph nodes in the neck (cervical nodes) or to lymph nodes in the upper chest (superior mediastinal nodes) or behind the throat (retropharyngeal nodes) (N1b), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back toward the spine or into nearby large blood vessels (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor is any size and might or might not have grown outside the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Anaplastic (undifferentiated) thyroid cancer

All anaplastic thyroid cancers are considered stage IV, reflecting the poor prognosis of this type of cancer.

Stage IVA (T4a, any N, M0): The tumor is still within the thyroid (T4a). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor has grown outside the thyroid (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor might or might not have grown outside of the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Recurrent cancer

This is not an actual stage in the TNM system. Cancer that comes back after treatment is called recurrent (or relapsed). If thyroid cancer returns it is usually in the neck, but it may come back in another part of the body (for example, lymph nodes, lungs, or bones). Doctors may assign a new stage based on how far the cancer has spread, but this is not usually as formal a process as the original staging. The presence of recurrent disease does not change the original, formal staging.

If you have any questions about the stage of your cancer or how it affects your treatment options, be sure to ask your doctor.


Last Medical Review: 02/24/2014
Last Revised: 03/20/2014