TNM Staging for melanoma skin cancer

The stage of a melanoma skin cancer tells you how thick it is and if it has spread. It helps your doctor decide the best treatment for you.

TNM stands for Tumour, Node, Metastasis.

TNM staging for melanoma skin cancer is complicated. Talk to your doctor or specialist nurse about your diagnosis. They can help you to understand more about the TNM stage of the melanoma.

Doctors might also use a number staging system. This has 5 different stages - from stage 0 to stage 4.

They might also use a scale to describe how deeply the melanoma has grown into your skin. This is called the Breslow thickness.

Tumour (T)

The skin is made up of 2 main layers. These are called the epidermis and dermis. The thickness of the epidermis and dermis varies depending on which part of the body the skin is covering. This means that how far a melanoma goes into these layers will also vary. 

Tumour describes the thickness of the melanoma. It also describes if the skin over the tumour is broken when looked at under a microscope (ulcerated) or not.

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 your doctors can no longer see the melanoma at the place it started (primary site). Or tests show that you have a melanoma that has spread, but your doctors do not know where it started.

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

T1a means the melanoma is less than 0.8 mm thick and the skin over it does not look ulcerated.

T1b means either:

• the melanoma is less than 0.8 mm thick and is ulcerated
• the melanoma is between 0.8 mm and 1 mm thick and may or may not be ulcerated

T2 means the melanoma is more than 1 mm thick up to 2 mm thick.

T3 means the melanoma is more than 2 mm thick up to 4 mm thick.

T4 means the melanoma is more than 4 mm thick.

T2, T3 and T4 melanomas are further divided into a and b. This depends on whether the melanoma is ulcerated or not - a means without ulceration, b means with ulceration.

Node (N)

Node describes whether cancer cells are in the nearby lymph nodes .

Where a cancer starts is called the primary tumour. Areas of cancer that have spread to another part of the body from the primary tumour are called metastases.

Doctors look for cancer cells in the nearby lymph nodes. In melanoma, they also look at whether the cancer has spread to the area between the primary tumour and the nearby lymph nodes. They use different terms for this. These are:

• microsatellite metastases
• satellite metastases
• in-transit metastases

Microsatellite metastases mean that your doctor can see melanoma cells next to the primary tumour when they look at it under a microscope. These cancer cells are not touching 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. These cells are not touching the primary tumour.

In-transit metastases mean the melanoma has spread to an area more than 2 cm away from the primary tumour. But it has not reached the nearby lymph nodes.

There are 4 main N stages in melanoma:

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

N1 means one of the following:

• there are melanoma cells in one lymph node
• there are in-transit, satellite or microsatellite metastases

N2 means there are melanoma cells in either:

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

N1, N2 and N3 can each be further divided into a, b or c. This depends on whether your doctor found the spread to the lymph nodes on your scans or in a sentinel lymph node biopsy. And whether you have any in-transit, satellite or microsatellite metastases.

Metastasis (M)

Metastasis (M) describes whether the cancer has spread to a different part of the body such as the liver or lungs.

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 into a, b, c or d. This depends on which parts of the body the cancer has spread to.

Treatment

The stage of the cancer helps your doctor decide what treatment you need. Treatment also depends on where the melanoma is and your general health and fitness.

Surgery is the main treatment for people with melanoma that has not spread (early melanoma). You usually have other treatment if:

• the melanoma is at high risk of coming back
• you are unable to have surgery
• the melanoma has spread to another part of the body (advanced melanoma)

Other treatments include:

• targeted cancer drugs
• immunotherapy
• chemotherapy
• radiotherapy
• cryotherapy
• other local treatments such as isolated limb infusion or perfusion

You may have treatment as part of a clinical trial.