ABC Health & Wellbeing

Fact File

Skin cancer

by Peter Lavelle

Skin cancer occurs when the UV light in sunlight damages the DNA in skin, causing skin cells to mutate and grow into cancers. It's the most common form of cancer in Australia, and Australians have the highest incidence in the world.

Published 27/02/2003

[Image source: iStockphoto]

• Background
• Basal cell carcinoma
• Squamous cell carcinoma
• Melanoma
• Preventing skin cancer
• More info

Background

The sun is as essential to life as water and oxygen. It keeps us warm, gives us energy by driving the food chain from which we get our food, and helps to maintain the habitats we live in.

It also has a psychological effect; sunlight makes us feel good. Studies have shown people are less likely to get depressed if they live in a warm and sunny climate.

And it allows our skin to manufacture Vitamin D, which is essential for a range of metabolic processes, such as making strong bones.

But there's a downside. The ultraviolet light in sunlight damages the DNA in skin, causing skin cells to mutate and grow into cancers.

Over millions of years, humans have evolved a mechanism for filtering out ultraviolet (UV) light. The protection comes from specialised skin cells called melanocytes. These produce a dark pigment called melanin, which absorbs the UV light and prevents it from doing damage to skin cells.

There's a danger that if the skin produces too much melanin, we won't make enough Vitamin D and we'll get Vitamin D deficiency diseases like osteomalacia and rickets. So we've developed just enough melanin to allow sufficient sunlight in the skin to make Vitamin D, without allowing too much sunlight to cause skin cancer. The sunnier our environment, the more melanin we need to achieve this balance and the darker our skin appears.

But the mass migration of peoples in the 19th and 20th centuries has wreaked havoc with the delicate melanin balance that has evolved over time. When people who live in areas with a lot of sunlight – sub-Saharan Africa, for example – move to northern European climates, they tend to get Vitamin D deficiency. Conversely, when fair-skinned people – Anglo Celtics and Europeans, for example – migrate to hotter climates, rates of skin cancer go up.

This is why Australians have the highest incidence of skin cancer in the world, and why skin cancer is the most common form of cancer in Australia. One in two Australians will develop a skin cancer at some time in their lives. Those most at risk are:

• people with fair skin and blue eyes (they have the least amount of melanin)
• people with a lot of outdoors exposure – such as farm workers, construction workers and people who work on fishing boats
• urban indoor workers who spend weekends or holidays in the sun
• people who were sunburnt or were in the sun a lot when they were children (exposure to sun in childhood and adolescence does the most damage).

There are three types of skin cancer, named after the type of skin cell from which they are derived.

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Basal cell carcinoma (BCC)

Basal cell carcinomas are the most common type, accounting for about 90 per cent of all skin cancers. They arise from the skin cells at the bottom (or basal) layers of the skin – hence the name.

BCCs are found most commonly on the ears, nose, and other exposed parts of the body – especially the face and neck. They look like a small, slow-growing shiny pink or pearly lump, which often develops an ulcerated centre. Sometimes they can look like a reddish scaly area of skin. They are more common in older people.

They do not spread beyond the skin, so are almost always harmless – although they can be unsightly, especially as they get larger, and occasionally they can penetrate quite deeply, producing what is known as a 'rodent ulcer'. For this reason, they are usually removed. This is usually done as a minor surgical procedure under local anaesthetic by a GP, a dermatologist or a surgeon. Alternatively the BCC can be removed by curettage (scraping off with a scalpel), cryotherapy (freezing with carbon dioxide 'snow' or liquid nitrogen) or cautery (burning).

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Squamous cell carcinoma (SCC)

Squamous cell carcinoma.

Squamous cell carcinomas arise from the outer layers of the skin. They are less common than basal cell carcinomas, but are more dangerous because they can spread to other parts of the body. They look like a red scaly sore that itches, weeps, and never seems to heal. They appear in areas most commonly exposed to the sun – the head, neck and upper back.

As they grow, SCCs can spread to lymph nodes (under the armpits, in the groin or in the neck, for example) or via the bloodstream to other organs.

For this reason they must be removed. This is usually done with surgery (by a GP, dermatologist or surgeon) under local anaesthetic, or with cryotherapy or cautery. If the cancer is larger, it may need to be removed under general anaesthesia by a surgeon and a skin graft placed over the wound. Radiotherapy, which uses X-rays to kill the cancer cells, is an alternative. If the SCC is found to have spread to lymph nodes, these need to be removed also.

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Melanoma

Melanoma is the least common type of skin cancer, but as cancers go, it is by no means a rarity. In fact, it is the fifth most common cancer in Australia (after non-melanocytic skin cancers, colorectal, prostate and breast cancer). And it is the most common cancer in men and women aged 15 to 44 years. Since it tends to run in families, genes are thought to play a role with some people inheriting a genetic predisposition to the disease.

Melanoma is a cancer of melanocytes – the melanin-producing cells in the skin. Hence, it usually looks dark brown, black or blue-black. It can be flat or raised and often has irregular borders.

A melanoma can arise on a patch of normal skin, or on an existing freckle or mole. Danger signs that a freckle or mole is turning cancerous include:

• a change of shape (becoming raised or getting more irregular borders)
• a change of colour (getting darker, for instance)
• bleeding or itching
• a mole appears for the first time over the age of 30.

A melanoma can arise anywhere in the body, not just on sites exposed to the sun. Sometimes it can arise on the sole of the foot, the palm of the hand or under the nails. It can grow quickly and spread to nearby lymph nodes, or via the bloodstream to distant organs like the bones, liver, lungs or brain. So of all the skin cancers, it is also the most dangerous. This makes early detection extremely important.

Melanoma.

GPs can usually tell a melanoma by its appearance. The GP will take a biopsy of the suspicious-looking area of skin and send it to a pathologist for confirmation. If it is a melanoma, and is found to be at an early stage, the GP or a surgeon will surgically remove it, plus an adequate safety margin, under local anaesthetic. If it has grown deeper into the skin, it may need to be removed with a wider section of skin around it. This is done under general anaesthetic in hospital by a surgeon. Sometimes a skin graft (taken from another part of the body) is used to replace the skin that has been removed.

Sometimes, if they are enlarged, the lymph nodes nearby are biopsied using a fine gauge needle, and if cancer is found then the lymph nodes are also removed. This is generally done surgically, although radiotherapy and/or chemotherapy are sometimes used in advanced cases, when spread to internal organs has occurred. Immunotherapy, which stimulates the body's immune system to fight cancer, is another approach but this is still at the research stage.

The outlook for a melanoma is good if it is found early. If a melanoma is removed when it is less than 1 mm deep the chances of cure are more than 95 per cent. Overall, 85 per cent of people found to have a melanoma will be alive five years from diagnosis. Anyone with a family history of melanoma and anyone who has multiple moles should be examined regularly by an appropriately trained and experienced doctor (such as a dermatologist).

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Preventing skin cancer

To minimise your chance of getting skin cancer:

• avoid the sun in the middle of the day (10 am to 3 pm) as much as possible (remember that snow, sand and water reflect sunlight onto skin, which is just as damaging as direct sun exposure)
• stay in the shade whenever possible
• wear protective clothing – a wide-brimmed hat and cover-up clothing, such as long-sleeved shirts and trousers (or at least knee-length shorts)
• apply SPF 30+, broad-spectrum sunscreen to the skin. Apply it 20 minutes or so before going outside and reapply every two hours whilst in the sun.

It is important to regularly examine your skin for signs of skin cancer, especially if you are in the older age group and/or you have sun-damaged skin or multiple moles and freckles.