Follicular Thyroid Cancer Staging
How is Follicular Thyroid Cancer Staged?
Staging is the process of finding out if and how far a cancer has spread. Follicular thyroid cancer staging is a critical factor in choosing follicular thyroid cancer treatment treatments, follicular thyroid cancer extent of surgery, and predicting your chance for cure.
Follicular thyroid cancer staging is based on the results of the physical examination, biopsy, imaging tests (ultrasound, radioiodine scan, CT scan, MRI, chest x-ray, and/or PET scans [which are described in the section Diagnosis of Follicular Thyroid Cancer]) and the pathologic findings of surgery itself .
Follicular thyroid cancer has a staging system that is not like other cancers. This staging system for follicular thyroid cancer takes into account the age of the patient. The current break point of age in the American Joint Committee on Cancer (AJCC) staging system for both follicular and papillary thyroid cancer is 45 years of age. More recent studies now suggest that this age cutoff is likely significantly higher at the 55 year age, thus newer follicular thyroid cancer and papillary thyroid cancer staging will likely reflect setting the age at this higher level, but until revised staging is established, 45 years of age is the AJCC break point.
The size of the follicular thyroid cancer within the thyroid gland itself and whether or not the cancer has spread into lymph nodes around the thyroid or sides of the neck is also included in the follicular thyroid staging system. The follicular thyroid cancer staging system also includes whether or not the cancer has spread into the fat and muscles around the thyroid (called local extension). Finally, follicular thyroid cancer staging includes the "differentiation" of the cancer which is what it looks like under a microscope and whether or not the thyroid cancer cells look mature or young and more "angry". The last component of follicular thyroid cancer staging is the presence of distant metastases, which means whether the cancer has spread to distant (far away) areas like the lungs, bone or liver.
In follicular thyroid cancer staging, and for that matter all cancer staging, the earlier the stage of disease is the more favorable and curable the cancer. Therefore, the lower/smaller the number, the better the chance for cure and long term survival.
The Follicular Thyroid Cancer 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. (Spread to lymph nodes is very very rare in follicular thyroid cancers)
- 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 follicular thyroid cancer (does not include 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.
N categories for follicular 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. The age cutoff for papillary thyroid cancer used to be 45 years of age but in more recent studies it has been established that the age is older and the new age to separate will soon be 55 years.
The prognosis of a follicular thyroid cancer patient under the age of 45 is excellent. The follicular thyroid cancer staging system takes this information into account, and classifies follicular thyroid cancer simply into two groups based on whether or not they have spread to distant sites:
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 in the body (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).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 in the body(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 any distant sites in the body(M1).