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TNM Staging

The TNM staging system is how the doctor stages your melanoma skin cancer.

The stage of a cancer tells your doctor how thick it is and how far it’s spread. It helps your doctor decide which treatment you need.

TNM staging for melanoma skin cancer is complicated. Talk to your doctor or specialist nurse about your diagnosis and to understand more about your TNM stage.

TNM stands for Tumour, Node, Metastasis.

Doctors might also use a number staging system.

Or they might use a scale to describe how deeply the melanoma has grown into your skin. These scales are called the Clark scale and the Breslow scale.

Tumour (T)

Tumour describes the thickness of the melanoma. There are 6 main stages of tumour thickness in melanoma – Tis to T4.

Tis means the melanoma cells are only in the very top layer of the skin surface. It is called melanoma in situ.

T0 means no melanoma cells can be seen where the melanoma started (primary site).

T1 means the melanoma is 1 mm thick or less. It is split into T1a and T1b.  

T1a means the melanoma is less than 0.8 mm thick and the skin over the tumour does not look broken under the microscope (not ulcerated).

T1b means either:

  • the melanoma is less than 0.8 mm thick but is ulcerated
  • the melanoma is between 0.8 mm and 1.0 mm and may or may not be ulcerated

T2 means the melanoma is between 1 mm and 2 mm thick.

T3 means the melanoma is between 2 mm and 4 mm thick.

T4 means the melanoma is more than 4 mm thick.

T2 and T4 melanoma is further divided into a and b depending on whether it is ulcerated or not. A means without ulceration, b means with ulceration

Diagram showing the T stages of melanoma without measurements

Mitotic rate of your melanoma

The staging system has been recently updated. It no longer includes the mitotic rate to work out your stage. But your doctor may still use it to work out how likely your cancer. is to spread. 

Mitotic rate means the number of cells that are dividing in a certain amount of melanoma tissue. Higher mitotic rate means that the melanoma is at greater risk the spreading because more cells are dividing.

Node (N)

The node stage describes whether cancer cells are in the nearby lymph nodes or lymphatic ducts. There are 4 main stages in melanoma.

Doctors also look at whether there are areas of cancer spread (metastases) between the primary tumour and the nearby lymph nodes. They use different terms for this:

  • microsatellite metastases
  • satellite metastases
  • in-transit metastases

Microsatellite metastases mean that under a microscope melanoma cells can be seen next to the primary tumour.

Satellite metastases mean that the melanoma cells have visibly spread to an area less than 2 cm away from the primary tumour.

In-transit metastases mean the melanoma has spread to an area more than 2 cm away from the primary tumour but before the nearby lymph nodes.

N0 means there are no melanoma cells in the nearby lymph nodes.

N1 means there are melanoma cells in one lymph node or there are in-transit, satellite or microsatellite metastases.

N2 means there are melanoma cells in 2 or 3 lymph nodes or there are melanoma cells in one lymph node and there are also in-transit, satellite or microsatellite metastases.

N3 means there are melanoma cells in 4 or more lymph nodes or there are melanoma cells in 2 or 3 lymph nodes and there are in-transit, satellite or microsatellite metastases or there are melanoma cells in any number of lymph nodes and they have stuck to each other (matted lymph nodes).

Metastasis (M)

Metastasis (M) describes whether the cancer has spread to a different part of the body.

There are 2 stages of metastasis – M0 and M1:

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. 

M1 can be further divided depending on which parts of the body the cancer has spread to and whether there are raised levels of a chemical in the blood called lactate dehydrogenase (LDH).

Treatment

The stage of your cancer helps your doctor to decide what treatment you need. Treatment also depends on:

  • where the melanoma is
  • your health and level of fitness

Surgery is the main treatment for people with melanoma that has not spread (early melanoma). You usually have other treatment if your melanoma is at high risk of coming back, unable to have surgery or has spread to another part of the body (advanced). Other treatments include:

  • targeted cancer drug
  • immunotherapy
  • chemotherapy
  • radiotherapy
  • laser therapy
  • cryotherapy
  • taking part in a clinical trial
Last reviewed: 
27 Jun 2019
  • AJCC Cancer Staging Manual (8th edition)
    American Joint Committee on Cancer
    Springer, 2017

  • Melanoma assessment and management
    National Institute for Health and Care Excellence, July 2015

  • BMJ Best Practice Melanoma
    BMJ Publishing Group LTD, June 2018

  • Cancer and its Management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

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