TNM Classification for Thyroid Cancer

The American Joint Committee on Cancer (AJCC) uses different tumor-node-metastasis (TNM) classification for differentiated and anaplastic thyroid cancer and for medullary thyroid cancer, as outlined below.^{[1, 2, 3]}

Table 1. TNM Classification for Differentiated and Anaplastic Thyroid Cancer (Open Table in a new window)

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor is found
T1	Tumor size ≤ 2 cm in greatest dimension and is limited to the thyroid
T1a	Tumor ≤ 1 cm, limited to the thyroid
T1b	Tumor > 1 cm but ≤ 2 cm in greatest dimension, limited to the thyroid
T2	Tumor size > 2 cm but ≤ 4 cm, limited to the thyroid.
T3	Tumor size > 4 cm, limited to the thyroid or any tumor with gross extrathyroidal extension invading only strap muscles
T3a	Tumor size > 4 cm, limited to the thyroid
T3b	Any size tumor with gross extrathyroidal extension invading only strap muscles (eg, extension to sternothyroid muscle or perithyroid soft tissues)
T4a	Any size tumor with gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4b	Any size tumor with gross extrathyroidal extension invading prevertebral fascia or encasing the carotid artery or mediastinal vessels
All categories may be subdivided: (s) solitary tumor and (m) multifocal tumor (the largest determines classification)
Regional lymph nodes (N)
Regional lymph nodes are the central compartment, lateral cervical, and upper mediastinal lymph nodes:
NX	Regional nodes cannot be assessed
N0	No regional lymph node metastasis
N0a	One or more cytologically or histologically confirmed benign lymph nodes
N0b	No radiologic or clinical evidence of locoregional lymph node metastasis
N1	Regional lymph node metastasis
N1a	Metastases to level VI or VI (pretracheal, paratracheal, or prelaryngeal/Delphian or upper mediastinal) lymph nodes
N1b	Metastases to unilateral, bilateral, or contralateral neck lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph nodes
Distant metastasis (M)
M0	No distant metastasis is found
M1	Distant metastasis is present

Table 2. TNM Classification for Medullary Thyroid Cancer (Open Table in a new window)

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor is found
T1	Tumor size ≤ 2 cm in greatest dimension and is limited to the thyroid
T1a	Tumor ≤ 1 cm, limited to the thyroid
T1b	Tumor > 1 cm but ≤ 2 cm in greatest dimension, limited to the thyroid
T2	Tumor size > 2 cm but ≤ 4 cm, limited to the thyroid.
T3	Tumor size > 4 cm, limited to the thyroid or any tumor with gross extrathyroidal extension invading only strap muscles
T3a	Tumor size > 4 cm, limited to the thyroid
T3b	Any size tumor with gross extrathyroidal extension invading only strap muscles (eg, extension to sternothyroid muscle or perithyroid soft tissues)
T4a	Moderately advanced disease; Any size tumor with gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4b	Very advanced disease; Any size tumor with extension toward the spine or into nearby large blood vessels, gross extrathyroidal extension invading prevertebral fascia or encasing the carotid artery or mediastinal vessels

Regional lymph nodes (N)
Regional lymph nodes are the central compartment, lateral cervical, and upper mediastinal lymph nodes:
NX	Regional nodes cannot be assessed
N0	No regional lymph node metastasis
N0a	One or more cytologically or histologically confirmed benign lymph nodes
N0b	No radiologic or clinical evidence of locoregional lymph node metastasis
N1	Regional lymph node metastasis
N1a	Metastases to level VI or VI (pretracheal, paratracheal, or prelaryngeal/Delphian or upper mediastinal) lymph nodes; can be unilateral or bilateral disease
N1b	Metastases to unilateral, bilateral, or contralateral neck lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph nodes
Distant metastasis (M)
M0	No distant metastasis is found
M1	Distant metastasis is present

Table3. Stage grouping (Open Table in a new window)

Stage grouping
Differentiated, medullary, and anaplastic carcinoma have separate stage groupings
Differentiated (age < 55y):
Stage	T	N	M
I	Any T	Any N	M0
II	Any T	Any N	M1
Differentiated (age ≥ 55y):
Stage	T	N	M
I	T1	N0/NX	M0
I	T2	N0/NX	M0
II	T1	N1	M0
	T2	N1	M0
	T3a/T3b	Any N	M0
III	T4a	Any N	M0
IVA	T4b	Any N	M0
IVB	Any T	Any N	M1
Anaplastic carcinoma (all anaplastic carcinomas are considered stage IV):
Stage	T	N	M
IVA	T1-T3a	N0/NX	M0
IVB	T1-T3a	Any N	M0
	T3b	Any N	M0
	T4	Any N	M0
IVC	Any T	Any N	M1
Medullary carcinoma:
Stage	T	N	M
I	T1	N0	M0
II	T2, T3	N0	M0
III	T1-T3	N1a	M0
IVA	T4a	Any N	M0
IVA	T1-T3	N1b	M0
IVB	T4	N0	M0
IVC	Any T	Any N	M1

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Table 1. TNM Classification for Differentiated and Anaplastic Thyroid Cancer

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor is found
T1	Tumor size ≤ 2 cm in greatest dimension and is limited to the thyroid
T1a	Tumor ≤ 1 cm, limited to the thyroid
T1b	Tumor > 1 cm but ≤ 2 cm in greatest dimension, limited to the thyroid
T2	Tumor size > 2 cm but ≤ 4 cm, limited to the thyroid.
T3	Tumor size > 4 cm, limited to the thyroid or any tumor with gross extrathyroidal extension invading only strap muscles
T3a	Tumor size > 4 cm, limited to the thyroid
T3b	Any size tumor with gross extrathyroidal extension invading only strap muscles (eg, extension to sternothyroid muscle or perithyroid soft tissues)
T4a	Any size tumor with gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4b	Any size tumor with gross extrathyroidal extension invading prevertebral fascia or encasing the carotid artery or mediastinal vessels
All categories may be subdivided: (s) solitary tumor and (m) multifocal tumor (the largest determines classification)
Regional lymph nodes (N)
Regional lymph nodes are the central compartment, lateral cervical, and upper mediastinal lymph nodes:
NX	Regional nodes cannot be assessed
N0	No regional lymph node metastasis
N0a	One or more cytologically or histologically confirmed benign lymph nodes
N0b	No radiologic or clinical evidence of locoregional lymph node metastasis
N1	Regional lymph node metastasis
N1a	Metastases to level VI or VI (pretracheal, paratracheal, or prelaryngeal/Delphian or upper mediastinal) lymph nodes
N1b	Metastases to unilateral, bilateral, or contralateral neck lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph nodes
Distant metastasis (M)
M0	No distant metastasis is found
M1	Distant metastasis is present

Table 2. TNM Classification for Medullary Thyroid Cancer

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor is found
T1	Tumor size ≤ 2 cm in greatest dimension and is limited to the thyroid
T1a	Tumor ≤ 1 cm, limited to the thyroid
T1b	Tumor > 1 cm but ≤ 2 cm in greatest dimension, limited to the thyroid
T2	Tumor size > 2 cm but ≤ 4 cm, limited to the thyroid.
T3	Tumor size > 4 cm, limited to the thyroid or any tumor with gross extrathyroidal extension invading only strap muscles
T3a	Tumor size > 4 cm, limited to the thyroid
T3b	Any size tumor with gross extrathyroidal extension invading only strap muscles (eg, extension to sternothyroid muscle or perithyroid soft tissues)
T4a	Moderately advanced disease; Any size tumor with gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4b	Very advanced disease; Any size tumor with extension toward the spine or into nearby large blood vessels, gross extrathyroidal extension invading prevertebral fascia or encasing the carotid artery or mediastinal vessels

Regional lymph nodes (N)
Regional lymph nodes are the central compartment, lateral cervical, and upper mediastinal lymph nodes:
NX	Regional nodes cannot be assessed
N0	No regional lymph node metastasis
N0a	One or more cytologically or histologically confirmed benign lymph nodes
N0b	No radiologic or clinical evidence of locoregional lymph node metastasis
N1	Regional lymph node metastasis
N1a	Metastases to level VI or VI (pretracheal, paratracheal, or prelaryngeal/Delphian or upper mediastinal) lymph nodes; can be unilateral or bilateral disease
N1b	Metastases to unilateral, bilateral, or contralateral neck lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph nodes
Distant metastasis (M)
M0	No distant metastasis is found
M1	Distant metastasis is present

Table3. Stage grouping

Stage grouping
Differentiated, medullary, and anaplastic carcinoma have separate stage groupings
Differentiated (age < 55y):
Stage	T	N	M
I	Any T	Any N	M0
II	Any T	Any N	M1
Differentiated (age ≥ 55y):
Stage	T	N	M
I	T1	N0/NX	M0
I	T2	N0/NX	M0
II	T1	N1	M0
	T2	N1	M0
	T3a/T3b	Any N	M0
III	T4a	Any N	M0
IVA	T4b	Any N	M0
IVB	Any T	Any N	M1
Anaplastic carcinoma (all anaplastic carcinomas are considered stage IV):
Stage	T	N	M
IVA	T1-T3a	N0/NX	M0
IVB	T1-T3a	Any N	M0
	T3b	Any N	M0
	T4	Any N	M0
IVC	Any T	Any N	M1
Medullary carcinoma:
Stage	T	N	M
I	T1	N0	M0
II	T2, T3	N0	M0
III	T1-T3	N1a	M0
IVA	T4a	Any N	M0
IVA	T1-T3	N1b	M0
IVB	T4	N0	M0
IVC	Any T	Any N	M1