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Diagnosis - Skin cancer (melanoma)

A diagnosis of melanoma will usually begin with an examination of your skin.

Some GPs take digital photographs of a suspected tumour so they can email them to a specialist for assessment.

As melanoma is a relatively rare condition, many GPs will only see a case every few years. It's important to monitor your moles and return to your GP if you notice any changes. Taking photos to document any changes will help with diagnosis.

Seeing a specialist

You'll be referred to a dermatology clinic for further testing if melanoma is suspected. You should see a specialist within 2 weeks of seeing your GP.

A skin specialist (dermatologist) or plastic surgeon will examine the mole and the rest of your skin. They may remove the mole and send it for testing (biopsy) to check whether it's cancerous. A biopsy is usually done using local anaesthetic to numb the area around the mole, so you will not feel any pain.

If cancer is confirmed, you'll usually need another operation, most often done by a plastic surgeon, to remove a wider area of skin. This is to make absolutely sure that no cancerous cells are left behind in the skin.

Further tests

You'll have further tests if there's a concern that the cancer has spread into other organs, bones or your blood.

Sentinel lymph node biopsy

If melanoma spreads, it will usually begin spreading through channels in the skin (lymphatics) to the nearest group of glands (lymph nodes). Lymph nodes are part of the body's immune system. They help remove unwanted bacteria and particles from the body and play a role in activating the immune system.

A sentinel lymph node biopsy is a test to determine whether microscopic amounts of melanoma (less than would show on any X-ray or scan) have spread to your lymph nodes. It's usually done by a specialist plastic surgeon, while you're under general anaesthetic.

A combination of blue dye and a weak radioactive chemical is injected around your scar. This is usually done just before the wider area of skin is removed. The solution follows the same channels in the skin as any melanoma.

The first lymph node the dye and chemical reaches is known as the "sentinel" lymph node. The surgeon can locate and remove the sentinel node, leaving the others intact. The node is then examined for microscopic specks of melanoma (this process can take several weeks).

If the sentinel lymph node is clear of melanoma, it's extremely unlikely that any other lymph nodes are affected. This can be reassuring, because if melanoma reaches the lymph nodes, it's more likely to spread elsewhere.

If the sentinel lymph node contains melanoma, there's a risk that other lymph nodes in the same group will also contain melanoma.

Your surgeon should discuss the pros and cons of having a sentinel lymph node biopsy before you agree to having it. 

Lymph node dissection or completion lymphadenectomy

An operation to remove the remaining lymph nodes in the group is known as a completion lymph node dissection or completion lymphadenectomy. Again, you should discuss the pros and cons of the procedure with your surgeon.

Other tests you may have include:

Cancer Research UK has more information about test to diagnose melanoma and tests to stage melanoma.

Melanoma stages

Healthcare professionals use a staging system called the AJCC system to describe how far melanoma has grown into the skin (the thickness) and whether it has spread. The type of treatment you receive will depend on what stage the melanoma has reached.

Melanoma stages are described as:

  • Stage 0 – the melanoma is on the surface of the skin
  • Stage 1A – the melanoma is less than 1mm thick
  • Stage 1B – the melanoma is 1mm to 2mm thick, or less than 1mm thick and the surface of the skin is broken (ulcerated) or its cells are dividing faster than usual
  • Stage 2A – the melanoma is 2mm to 4mm thick, or it's 1mm to 2mm thick and ulcerated
  • Stage 2B – the melanoma is thicker than 4mm, or it's 2mm to 4mm thick and ulcerated
  • Stage 2C – the melanoma is thicker than 4mm and ulcerated
  • Stage 3A – the melanoma has spread into 1 to 3 nearby lymph nodes, but they're not enlarged; the melanoma is not ulcerated and has not spread further
  • Stage 3B – the melanoma is ulcerated and has spread into 1 to 3 nearby lymph nodes but they're not enlarged, or the melanoma is not ulcerated and has spread into 1 to 3 nearby lymph nodes and they are enlarged, or the melanoma has spread to small areas of skin or lymphatic channels, but not to nearby lymph nodes
  • Stage 3C – the melanoma is ulcerated and has spread into 1 to 3 nearby lymph nodes and they're enlarged, or it's spread into 4 or more nearby lymph nodes
  • Stage 4 – the melanoma cells have spread to other parts of the body, such as the lungs, brain or other areas of the skin

Cancer Research UK has more information about the stages of melanoma.

Page last reviewed: 7 February 2020
Next review due: 7 February 2023