How is Anaplastic Thyroid Cancer Staged?
Anaplastic thyroid cancer is one of the most lethal cancers known to man and the staging system reflects this fact. Only the earliest stage of anaplastic thyroid cancers should be considered for surgical therapy. Any evidence of distant spread of anaplastic thyroid cancer makes anaplastic thyroid cancer a non-surgical disease. As with any valid staging system, accurate staging predicts chance of cure.
Anaplastic thyroid cancer staging is based on the results of the physical examination, biopsy, imaging tests (ultrasound, CT scans, MRIs, and PET scans [which are described in the section Diagnosis of Anaplastic Thyroid Cancer.
Because anaplastic thyroid cancers are such aggressive and often rapidly lethal cancers, there is no such thing as an early stage anaplastic thyroid cancer. In general, the lower/smaller the number in staging, the better the chance for cure and long term survival. However, all anaplastic thyroid cancers are by definition stage IV disease as their potential to spread and rapidly become lethal is so commonplace. Unlike other thyroid cancers where age is a major factor, in anaplastic thyroid cancer age has no role in regards to staging or prognosis.
Size has no relevance in the staging of anaplastic thyroid cancer either!!!! However, the anaplastic thyroid cancer staging system does include whether or not the cancer has remained confined to the thyroid gland or whether it has extended outside of the gland itself whatsoever (the most common case). The last component of anaplastic 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.
The Anaplastic (undifferentiated) 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 whether the anaplastic thyroid cancer is (there is no role for size in staging of anaplastic thyroid cancer)
- T4A :confined to the thyroid gland
- T4B:extended outside of the thyroid gland to any extent
- 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 anaplastic (undifferentiated) thyroid cancer
TX: Primary tumor cannot be assessed.
T4a: The tumor is any size and is confined to the thyroid gland itself
T4b: The tumor is any size and has extended (to any degree) outside of the thyroid gland itself.
N categories for anaplastic (undifferentiated) 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 anaplastic 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.
For anaplastic (undifferentiated thyroid cancer) age of patient and size of tumor has no role in staging. Further, in anaplastic thyroid cancer, all patients are by definition at least stage IVA disease. There is no such thing as an early stage diagnosis of anaplastic 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).