Decorative image

TNM staging

The stage of a cancer tells you about its size and whether it has spread. It helps your doctor to decide which treatment you need. Your stage is worked out by looking at tissue from your thyroid and the results of your scans. 

It might not be possible to fully stage your cancer until after your surgery.

Doctors use the TNM system to stage thyroid cancer. TNM stands for:

  • Tumour 
  • Node
  • Metastasis

Doctors may also use another system called the number staging system. This system divides cancers into 4 groups, from stage 1 to stage 4.

Tumour (T)

T describes the size of the tumour. 

Tx means the tumour cannot be assessed. 

T0 means there is no sign of a tumour.

T1 means the cancer is within the thyroid gland and is 2cm or less. T1 tumours are further divided into T1a and T1b.

T1a

T1a means the tumour is completely inside the thyroid and is up to 1cm across.

Diagram showing stage T1a thyroid cancer

T1b

T1b means the tumour is completely inside the thyroid and is between 1cm and 2cm across.

Diagram showing stage T1b thyroid cancer

T2

T2 means the tumour is entirely inside the thyroid. It is more than 2cm but no greater than 4cm across.

Diagram showing stage T2 thyroid cancer

T3

T3 is divided into T3a and T3b.

T3a

T3a means the tumour is more than 4cm across but is still inside the thyroid.

Diagram showing T3a thyroid cancer

T3b

T3b means the tumour is any size and has grown into one or more of the muscles beside the thyroid (strap muscles).

T4

T4 tumours have grown outside the thyroid and are divided into T4a and T4b.

T4a

T4a means the cancer has grown outside the thyroid into nearby soft tissue, such as the voice box (larynx), windpipe (trachea), food pipe (oesophagus) or the voice box nerve (recurrent laryngeal nerve).

Diagram showing stage T4a thyroid cancer

T4b

T4b means the cancer has grown outside the thyroid into the area surrounding the bones of the spine or one of the main blood vessels in the neck area.

Diagram showing stage T4b thyroid cancer

Node (N)

N describes whether the cancer has spread to the lymph nodes Open a glossary item.

Nx means that there is no information about nearby lymph nodes.

N0 means that the cancer hasn't spread to nearby lymph nodes.

N1 means the cancer has spread to nearby lymph nodes. It is divided into 2 groups.

N1a

N1a means the cancer has spread to lymph nodes close to the thyroid in the neck (called the pretracheal, paratracheal, and prelaryngeal lymph nodes) or in the upper chest (the superior mediastinal nodes). 

Diagram showing stage N1a thyroid cancer

N1b

N1b means the cancer has spread to other lymph nodes in the neck (called cervical nodes) or to lymph nodes behind the throat (retropharyngeal).

Diagram showing stage N1b thyroid cancer

Metastases (M)

Metastases describes whether the cancer has spread to a different part of the body.

M0 means the cancer hasn’t spread to another part of the body.

M1 means the cancer has spread to another part of the body, such as the lungs or bones.

Diagram showing stage M1 thyroid cancer
Last reviewed: 
06 Apr 2021
Next review due: 
08 Apr 2024
  • American Joint Committee on Cancer (AJCC) Staging Manual (8th edition)
    S Edge and others (Editors)
    Springer, 2017

  • Thyroid cancer: ESMO clinical practice guidelines for diagnosis, treatment and follow up.
    S Filetti and others
    Annals of Oncology, 2019. Volume 30. Pages 1856-1883

  • Management of thyroid cancer: United Kingdom National Multidisciplinary Guidelines
    AL Mitchell and others
    Journal of Laryngology and Otology, 2016. Volume 130, Supplement 2, Pages 150 to 160

  • On the use and abuse of X in the TNM classification

    F Greene and others

    Cancer 2005 Volume103, Issue3 Pages 647-649