Skin Cancer (Malignant Skin Melanoma)

What is Skin Cancer?

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Melanomas are cancers of cells known as 'melanocytes' that are present in the skin. The purpose of the melanocytes is to produce a dark pigment called melanin. Melanin is important for protecting DNA (a very complex chemical that determines what a cell does) from the damaging ultraviolet radiation from the sun. Melanin is the primary determining factor in someone's skin colour - the more melanin in the skin, the darker it will appear.

Sometimes, however, something can go wrong in a melanocyte. It becomes cancerous and grows very quickly, becoming bigger and bigger. The cancerous cells can eventually spread to other parts of the body where they can keep growing, causing damage to the surrounding structures. It is important to be able to recognise the signs of a melanoma while it is still local. If it has not yet spread, there is a better chance of removing all the cancerous cells.

There are actually several different types of melanoma, each with different patterns of growth and different areas that they grow in. That is why it is important for you to see your GP if you are at all worried about any areas of pigmentation on your skin.

Melanoma

Statistics on Skin Cancer?

Malignant melanomas are the most serious form of skin cancer, because while they only account for around 4% of skin cancers, they are responsible for 80% of deaths related to skin cancer. Add to this that only 14% of patients in whom the disease has metastasised (spread to other parts of their body) survive for 5 years, and you get a picture of how serious they can be.

Melanoma is also one of the most frequently occurring cancers in Australia. Men have a 1 in 26 chance, and women a 1 in 36 chance, of developing a melanoma before they are 75. The typical age range is between 30-50 years, with the average being 40 years. Skin cancer is rare before the age of 20. The chance of developaing a melanoma increases with age, but it can still occur in younger people.

Risk Factors for Skin Cancer

Two thirds of all melanomas can be attributed to sun exposure. It may seem strange, but people who go out into the sun episodically (e.g. going to the beach every weekend) are actually at a higher risk than people who have had more regular and long-term exposure (e.g. a farmer).

You are more at risk if you burn very easily and are particularly 'sun sensitive'. This is thought to be due to the damage that is caused to the skin by the ultraviolet radiation of the sun.

There are other strong risk factors for melanoma. A family history of melanoma puts you at much higher risk than other people. Also, if you have a lot of moles or have previously had a melanoma, there is a higher risk of melanoma. If you are on immunosuppressive medication then your body is less able to fight off the cancerous cells and you are more likely to get a melanoma.

Progression of Skin Cancer

A melanoma will initially be confined to the surface of the skin, with the melanocytes multiplying and forming an expanding area of dark pigmentation. If left untreated, it can grow vertically (that is, into the skin rather than across it) and get into some of the deeper structures. Some of the cells can then break off the initial melanoma and get into the blood stream or the lymphatic system. These provide 'pathways' down which the cells can spread to other parts of the body. Sometimes 'satellite' melanomas can be seen, where they begin to appear in small islands away from the original site. The cells can spread to the lymph nodes, where they can form small hard lumps of dense cells. They can then also spread to other organs of the body, particularly those with high blood supply such as the brain, the bones and the liver. The cancer can cause large amounts of damage in these locations.

Symptoms of Skin Cancer

The ABCDE system is generally used to determine if a lesion is likely to be a melanoma or not. The following things are taken into account and summarised in the diagram below:

Asymmetry

A melanoma is almost always asymmetrical (that is, the opposite sides are not equal in size or shape), with the opposite segments being obviously different.

Border

The border of a melanoma should be assessed for regularity and colour. A melanoma usually has well defined borders or solid colour, whereas the border in a more benign lesion may be ill-defined and fade into the colour of surrounding skin. The border of a melanoma is usually irregular in shape, while most benign lesions have a regular edge.

Colour

Colour variation within the lesion is an important sign. Colours such as grey, violet, red, orange and white may appear within the darker blue-black background. A narrow red halo may sometimes be seen around a melanoma. Sometimes a melanoma may not have any pigment (called amelanocytic) and this can make the diagnosis much trickier.

Diameter

Most melanomas are between 6-7mm when first diagnosed but nodular lesions may be diagnosed early.

Elevation

Elevation of a lesion indicates invasion and is a poor prognostic sign. It is important to diagnose a lesion before it begins to elevate.

Clinical Examination of Skin Cancer

When a doctor is examining a patient for melanomas, they should look at all lesions on the skin, not just the one that the patient is concerned about.

The examination should be conducted in an area with good lighting and with some form of magnification. Sometimes the doctor will be using a set of magnifying glasses or even a dermatoscope (a special skin microscope) but this requires special training and, while useful, is not necessary for assessing lesions.

The examination should begin at your head, examining the hairline, ears, neck, back and the arms. The back of the legs should also be examined. The front of your body should then be examined, looking at the hairline, ears, forehead, cheeks, chest and abdomen, and even under the pubic hair. The front of the legs can be examined next.

How is Skin Cancer Diagnosed?

The most useful investigation for a clinically suspicious melanocytic lesion is a biopsy. However, this should only be done if the doctor thinks that there is genuinely a chance that the lesion is a melanoma, as prophylactic removal of a benign lesion (removal of a lesion just 'in case' it turns into something serious) is not recommended. Surgical biopsy is the preferred option, as punch or shave biopsies will not have as favourable outcomes.

Prognosis of Skin Cancer

The prognosis of a melanoma depends on how advanced it is when it is found. The most important factor in this is the 'depth' of the cancer and whether there has been much vertical growth. Depending on how thick the cancer is, ten-year survival rates (that is, the chance that a person will still be alive 10 years after the diagnosis) vary between 100% for a melanoma that is still in the very top layer of the skin, down to 40% for the thickest melanoma. If the melanoma is ulcerated, has invaded the lymphatic system, has any 'satellite' lesions (other small islands of melanoma nearby) or is growing very quickly, then the outcome may be less favourable than if none of these things were present.

How is Skin Cancer Treated?

The primary treatment option is surgical excision, removing the lesion as well as a little bit of tissue around it to take out as many cancerous cells as possible, and hopefully stopping the lesion from regrowing.

Surgical excision of a melanoma

Treatment of lymph nodes should be through needle aspiration of suspicious nodes. If the nodes are found to contain cancer then they should also be surgically removed. Other surrounding nodes should also be removed as they may contain cancerous cells which have the potential to regrow.

If the cancer has spread to other parts of the body (metastasised) then management should be by an oncologist (a special cancer doctor) along with several other doctors. Sometimes you may be referred to a specialised melanoma centre, where they might want to try treatment with chemotherapy, immunotherapy or radiotherapy.

Surgical removal of lesions in other parts of the body may be considered if the lesions appear in the lungs, brain or peritoneum.

There was initially some hope that 'interferon' therapy that would help the body defend itself from the cancerous cells, but further trials into this have, unfortunately, shown no clear benefit.

Skin Cancer References

Clinical Practice Guidelines: The management of cutaneous melanoma: National Health and Medical Research Council; 1999.
Epidimiology of Cancer in South Australia. Incidence, mortality and survival 1977-1995. Incidence and mortality 1995. Adelaide: South Australian Cancer Registry; 1996.
Kumar, P and Clark, M. Clinical Medicine (Sixth ed). 2005, Elsevier Saunders: Edinburgh.
Miller, AJ and Mihm, MC. Melanoma. New England Journal of Medicine. 2006; (355): 51-65.
Murtagh, J. General Practice (Third ed). 2005, Mcgraw-Hill: Sydney.