Staging is based on the results of the physical exam, biopsy, and imaging tests (ultrasound, CT scan, MRI, chest x-ray, and/or nuclear medicine scans), which are described in the section, "How is thyroid cancer diagnosed?"
The TNM Staging System
A staging system is a standard way for the cancer care team to summarize how large a cancer is and how far it has spread. Ask your doctor to explain thyroid cancer staging in a way that you understand so that you can take a more active role in making informed decisions about your treatment.
The most common system used to describe the stages of cancers is the American Joint Committee on Cancer (AJCC) TNM system. The TNM system describes 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 small bean-shaped collections of immune system cells that are important in fighting infections. 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 site of spread of thyroid cancer is to the lungs. The next most common sites are 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 "cannot be assessed because the information is not available."
T Categories for Thyroid Cancer:
TX: Primary tumor cannot be assessed
TO: 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 between 2 cm and 4 cm (slightly less than 2 inches) across and has not grown out of the thyroid.
T3: The tumor is either larger than 4 cm or it has begun to grow a small amount into nearby tissues outside the thyroid.
T4a: A tumor of any size that 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: A tumor of any size that 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 Cancers:
T4a: Tumor is still within the thyroid.
T4b: Tumor has grown outside of the thyroid.
N Categories for Thyroid Cancer:
NX: Regional (nearby) lymph nodes cannot be assessed.
N0: No spread to nearby lymph nodes.
N1: The cancer has spread to nearby lymph nodes.
N1a: Spread to lymph nodes around the thyroid in the neck (called pretracheal, paratracheal, and prelaryngeal lymph nodes).
N1b: 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:
M0: No distant metastasis.
M1: Distant metastasis is present, involving distant lymph nodes, internal organs, bones, etc.
Stage Grouping: Once the values for T, N, and M are determined, they are combined to find the stage. Stage is expressed as a Roman numeral from I through IV, with letters used to divide a stage into substages. Unlike most other cancers, thyroid cancers are grouped into stages in a way that considers both the subtype of cancer and the patient's age.
Papillary or follicular thyroid carcinoma (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 papillary thyroid cancer, for example, are stage I if they have no distant spread and stage II if they have distant metastases beyond the neck or upper mediastinal lymph nodes.
- 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 thyroid carcinoma (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).
- 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).
- 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 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. It may or may 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 may 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 not to distant sites (M0).
- Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back to the spine or into nearby large blood vessels (T4b). It may or may 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 may or may not have grown outside the thyroid (any T). It may or may not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).
Medullary Thyroid Carcinoma:
- 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 2cm 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).
- 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 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 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 may or may 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 may 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 not to distant sites (M0).
Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back towards the spine or into nearby large blood vessels (T4b). It may or may 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 may or may not have grown outside the thyroid (any T). It may or may not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).
Anaplastic/undifferentiated thyroid carcinoma:
All anaplastic thyroid cancers are considered stage IV, reflecting the poor prognosis of this type of 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 and may be resectable (removable by surgery). It may or may 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 and is not resectable. It may or may 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 may or may not have grown outside of the thyroid (any T). It may or may not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).
Recurrent Thyroid Cancer
This is not an actual stage in the TNM system. Cancer that comes back after treatment is called recurrent (or relapsed). Thyroid cancer usually returns in the neck, but it may reappear 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, do not hesitate to ask your doctor.
Last Medical Review: 10/12/2010
Last Revised: 01/12/2011
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