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Causes & diagnosis

Causes and risks of melanoma

The main risk factor for melanoma is exposure to ultra violet (UV) light, through natural sunlight or artificially from sunbeds or lamps. UV light damages the DNA (genetic material) in our skin cells and can cause skin cancers like melanoma.

Sun exposure is not the cause of all melanomas because some melanomas affect parts of the body that arenít exposed to the sun.

Ultraviolet (UV) rays from the sun In the UK the number of people developing melanoma and other skin cancers is steadily rising. This may be because people take sunshine holidays abroad more often.

Ultraviolet light from sunbeds Sunbeds give off artificial UV rays which damage the DNA, increasing the risk of developing melanoma. The more you use a sunbed or lamp the greater your risk. Getting a sunbed tan before you go on holiday can actually increase your risk of melanoma.

Itís important for us all to be aware of the damage that too much exposure to the sun can cause. Some sunshine is good for us. It helps us make vitamin D which keeps bones and teeth healthy, and generally makes us feel better. But itís important to be aware of the damage that too much exposure to the sun can cause.

If youíve had a melanoma (or any skin cancer) or are at increased risk of melanoma, itís essential to protect yourself from the sun.

Other factors that can increase your risk

Your skin type People with fair skin, red or fair hair, blue eyes, and freckles are more sensitive to the sun. Because of their skin type they burn more easily and so are more at risk of getting melanoma. Having brown or black skin lowers your risk of getting melanoma, but it doesnít mean that you will never get one.

Sunburn Episodes of severe sunburn, especially during childhood, can increase the risk of melanoma in the future.

Having lots of moles and unusual moles People who have a lot of moles (especially over 100) have a higher risk of getting melanoma. People with moles which are bigger than usual, with an irregular shape or colour (called atypical), have an increased risk. These moles (sometimes called dysplastic naevi) rarely change into melanoma, but itís important to keep an eye on them. Having lots of moles and atypical moles can run in some families. Having a very large (more than 20cm in diameter) dark hairy mole which you were born with also increases your risk of melanoma.

If you have any of the above you can be referred to a skin specialist for advice and an assessment of your skin.

Family history of melanoma This increases your risk, especially if you have two or more close relatives who have had melanoma. This may be caused by an inherited faulty gene, but this area is still being researched. People with a very strong family history of melanoma can be referred by their GP to a family cancer clinic (which may be doing research).

Reduced immunity People with a weakened immune system because they have HIV, or people taking drugs that suppress the immune system (after an organ transplant) have an increased risk of melanoma.

Symptoms of melanoma

About half of melanomas start with a change in normal looking skin. This usually looks like a dark area or an abnormal new mole. The other half of melanomas develop from a mole or freckle that you already have.

It can be difficult to tell the difference between a melanoma and a normal mole. The following checklist (known as the ABCDE list) will give you an idea of what to look out for:

Asymmetry Ė Melanomas are likely to be irregular or asymmetrical. Ordinary moles are usually symmetrical (both halves look the same)

Border Ė Melanomas are more likely to have an irregular border with jagged edges. Moles usually have a well-defined regular border.

Colour Ė Melanomas tend to have more than one colour. They may have different shades like brown mixed with black, red, pink, white or a bluish tint. Moles are usually one shade of brown.

Diameter Ė Melanomas are usually more than 7mm in diameter. Moles are normally no bigger than the blunt end of a pencil (about 6mm across).

Evolving (changing) Ė Look for changes in the size, shape or colour of a mole.

See your doctor straight away if you have:

any of the ABCDE signs
a mole that is changing in size, shape or colour tingling or itching in a mole
crusting or bleeding in a mole
something growing under a nail or a new pigmented line in a nail.

Melanoma can usually be cured if itís found at an early stage.

How melanoma is diagnosed

Usually you will begin by seeing your GP who will examine you. If your GP thinks you may have a melanoma they should refer you urgently to a doctor with specialist training in diagnosing skin cancer.

Seeing a specialist
Giving your consent
Removing the mole (excision biopsy)

Seeing a specialist

If you have a suspected melanoma you should be seen within a couple of weeks by a skin cancer specialist. Your appointment will usually be at a skin clinic or at a pigmented lesion clinic (a special clinic for diagnosing melanomas early). You will see a skin specialist (dermatologist) or a plastic surgeon. These doctors are experienced in treating skin cancers.

Your specialist will examine your mole and ask you questions about how long youíve had it and the changes youíve noticed. They usually also examine the rest of your skin to see if you have any other unusual moles.

Some specialists may look at your moles with a small hand held instrument called a dermatoscope. This gives a bigger and clearer picture of the mole, but itís not always necessary to have this test. Your specialist will be able to tell a lot by just looking at your mole.

If they think you have a melanoma your specialist will ask you to have the whole mole removed (excision biopsy). You may also be introduced to a specialist skin cancer nurse who will give you information and support.

Giving your consent

Before your mole is removed, your doctor will explain the aims of the treatment to you. Youíll usually be asked to sign a form saying that you give your permission (consent) for the mole to be removed. Your doctors or specialist nurse will explain the procedure and talk to you about any possible complications, such as bleeding or infection, although these are unusual. Theyíll also explain that you will have a small scar as a result of having your mole removed.

Removing the mole (excision biopsy)

Once youíre lying down comfortably your doctor will inject a local anaesthetic around the area of the mole. After this they will cut out the whole mole and a tiny amount of skin around it (2Ė5mm). You wonít feel this because the local anaesthetic numbs the area. Your doctor will then close the wound using stitches, which will be removed after 5Ė14 days. Some people may have stitches which dissolve and donít need to be removed.

The mole is examined under the microscope by a pathologist to see if any melanoma cells are present. You usually get the results within a few weeks when you return to the clinic.

When itís confirmed that it was a melanoma your specialist may talk to you about having further surgery, known as a wide local excision. A wide local excision is done to make sure that all the melanoma cells in the area have been removed. This is explained in the section on treatment.

Staging melanoma

The stage of a cancer is a term used to describe the size of the cancer and whether it has spread. Knowing the stage of a cancer helps doctors decide on the best treatment for you. The staging system that is used for melanoma is the American Joint Committee on Cancer (AJCC).

AJCC staging system

This uses the TNM system

T stands for tumour. This is based on the thickness of the melanoma (using Breslow thickness) and also looks at whether the melanoma is ulcerated. N stands for spread to lymph nodes (sometimes called glands).

M is whether the melanoma has spread to other parts of the body (secondary or metastatic cancer).

Breslow thickness

As well as the AJCC system, an important measurement for melanoma is how thick it is. This is called the Breslow thickness (named after the doctor who introduced it). Itís the distance in millimetres from the surface of the skin to how far down the deepest melanoma cells are. Thin melanomas (less than 1mm) have a very high chance of being cured.


A melanoma is said to be ulcerated if the layer of skin covering the melanoma cannot be clearly seen. If itís not ulcerated the letter a is added to the stage and if it is ulcerated the letter b is added.

Thin melanoma, less that 1mm, is always stage 1 in the AJCC system. It will either be stage 1a or stage 1b depending on whether or not it is ulcerated.

Melanoma in situ

Melanoma in situ, or melanocytic intraepithelial neoplasia (MIN), is the very earliest stage of melanoma. The melanoma cells are just in the very top layer of skin

(epidermis) and havenít started to spread into the surrounding skin. Itís called a Stage 0 melanoma and itís sometimes described as precancerous. Lentigo maligna is a type of melanoma in situ.

Melanoma in situ can be cured and there shouldnít be any risk of it coming back after surgery.

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