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TNM Staging

Find out about tumour, node and metastasis (TNM) staging and treatment for melanoma skin cancer.

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 5 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

T1 means the melanoma is less than 1 mm thick

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

Diagram showing the T stages of melanoma

Ta and Tb

The T part is further divided into 2 groups, a and b, depending on ulceration. This describes whether or not the skin covering the tumour is broken.

Ta means the melanoma is not ulcerated

Tb means the melanoma is ulcerated

Thin melanomas (T1) are also staged depending on the mitotic rate. Mitotic rate means the number of cells that are in the process of dividing in a certain amount of melanoma tissue. A higher mitotic rate means that there are more cells that are dividing.

T1a melanomas are not ulcerated and have a mitotic rate of less than 1/mm (squared)

T1b melanomas have a mitotic rate of 1/mm (squared) or more

Ulcerated melanomas and those with a higher mitotic rate have a greater risk of spreading.

Node (N)

There are 4 stages describing whether cancer cells are in the nearby lymph nodes or lymphatic ducts – N0 to N3.

N0 means that the nearby lymph nodes don’t contain melanoma cells

N1 means there are melanoma cells in one lymph node

N2 means there are melanoma cells in 2 or 3 lymph nodes

N3 means there are melanoma cells in 4 or more lymph nodes

Na, Nb and Nc

The N part of the stage is further divided into groups a, b and c.

Na means the cancer in the lymph node can only be seen by microscope (micrometastasis)

Nb means there are obvious signs of cancer in the lymph node (macrometastasis)

Nc means that there are melanoma cells in small areas of skin very close to the primary melanoma (satelite metastases) or in the skin lymph channels (in transit metastases)

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 is split into M1a, M1b and M1c.

  • M1a means there are melanoma cells in the skin in other parts of the body or in lymph nodes far away from where the melanoma started growing
  • M1b means there are melanoma cells in the lung
  • M1c means there are melanoma cells in other organs, or the melanoma causes a high level of a chemical made by the liver (lactate dehydrogenase)


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

  • where the cancer is
  • other health conditions

Surgery is the main treatment for people with melanoma that has not spread (early melanoma).

If your cancer has spread (advanced melanoma), you might have:

  • biological therapy
  • chemotherapy
  • radiotherapy
Last reviewed: 
12 Nov 2015
  • Melanoma assessment and management
    National Institute for Health and Care Excellence, July 2015

  • Cancer: Principles and practice of oncology (10th edition)
    VT De Vita, TS Lawrence and SA Rosenberg
    Lippincott, Williams and Wilkins, 2015   

  • TNM Classification of Malignant Tumours (7th edition)
    International Union Against Cancer   
    L.H. Sobin, M.K. Gospodarowicz, Ch. Wittekind
    John Wiley & Sons, Hoboken, New Jersey, 2009

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