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Skin cancers (non-melanoma)

Sunday 30 December, 2007

Reviewed by: Dr Alvin H Chong (MBBS, M. Med, FACD) Consultant Dermatologist, Skin & Cancer Foundation Victoria. Senior Lecturer in Dermatology, Dept. of Medicine (Dermatology), St Vincent's Hospital, University of Melbourne.

The skin

The skin has many important functions. It protects us from disease, injury and changes in temperature.

The skin has 2 main layers. The outer layer is called the epidermis. It contains basal cells and squamous cells, which link tightly together to form the barrier, and melanocytes, which produce melanin, the substance that gives skin its colour. The layer underneath the epidermis is called the dermis. The dermis contains the roots of hairs, glands that make sweat and oil, blood and lymph vessels and nerves. Below this is a layer of fat.

What happens to skin in the sun?

Each time your unprotected skin is exposed to ultraviolet (UV) radiation, it causes changes to take place in the structure of the cells and in what they do. Through years of over exposure to UV radiation, the skin becomes permanently damaged. The more exposure, the worse the damage to the skin.

These changes are often described as ‘premature ageing', but they are, in fact, quite different from normal ageing in skin. In old age, the skin that has not been exposed to the sun is smooth, without spots or blemishes. It is a little thinner than younger skin, but there are relatively few wrinkles and it remains fairly firm.

Skin that has been exposed to the sun, on the other hand, becomes thickened, rough and leathery. Gradually, over 20 to 40 years, it acquires many blotches and blemishes and fair skin particularly may become yellowish. It becomes loose, and it's covered with fine wrinkles broken by a number of deep creases. These effects are seen especially on skin that gets the most sun - the face, the back of the neck, the backs of hands and arms and the neckline.

You can compare these 2 types of age-related change by looking at the non-sun-exposed skin on your inner arm near the armpit, and then the sun-exposed skin on the face.

Skin exposed to sun over time may also develop scaly red ‘sunspots' or solar keratoses.

Solar keratoses (‘sunspots')

They appear on areas of skin that are frequently in the sun - most commonly the face, ears, neck, forearms or hands. The spots vary in size: usually from a few millimetres to 2 centimetres across. They may sometimes be painful or itchy, and may sting when in the sun or if they are scratched. Solar keratoses are not skin cancers, but like skin cancers, they are the result of exposure to the sun. Rarely, they may change into a skin cancer. They may remain for years or disappear and reappear over the years.

Solar keratoses are a warning sign that you are at risk of skin cancer: skin cancers are more common in people with solar keratoses. If you have a solar keratosis, you should watch out for other signs of early skin cancers.

Skin cancer

The epidermis contains 3 different types of cells: squamous cells, basal cells and melanocytes, each of which can turn cancerous. Skin cancers are named after the type of cell from which they start. The 3 main types of skin cancer are basal cell carcinoma, squamous cell carcinoma and-the most serious skin cancer-melanoma.

Melanoma is not discussed in detail here, refer to our melanoma page.

Melanoma

Melanoma develops in the melanocytes. It can occur anywhere on the body. It may grow quickly and, if it is not treated, may spread to other parts of the body to form new, secondary cancers.

Basal cell carcinoma

Basal cell carcinoma is the most common but least dangerous type of skin cancer. About 75% of skin cancers in Australia are basal cell carcinomas. They grow slowly over months or years and very rarely spread to other parts of the body. However if they are not treated, they may form an ulcer (a break in the surface of the skin); as this deepens, it may cause damage to tissue and organs nearby-for instance, the eyelids or nose.

Basal cell carcinomas occur most often on the head, neck or upper body, though they may appear on other parts of the body. They usually start as small, round or flattened lumps that are red, pale or pearly in colour, and may have blood vessels on the surface. A basal cell carcinoma may also appear as a small area of red and scaly skin, similar to a patch of eczema.

If you have one basal cell carcinoma, you are likely to have others, either at the same time or in later years. Basal cell carcinomas are most common in people over 40 years, but also occur in younger adults. Basal cell carcinomas are easily treated if detected early.

Squamous cell carcinoma

Squamous cell carcinomas are less common than basal cell carcinomas but are potentially more dangerous. They grow more quickly, usually over weeks or months and may spread to nearby lymph nodes or other parts of the body if not treated promptly. They occur most often (but not only) on the head, neck, hands and forearms.

A squamous cell carcinoma looks like a red scaly spot, usually thickened, which may bleed easily or ulcerate after some time. It may be tender to touch. Squamous cell carcinomas rarely occur before 40 years of age.

Causes of skin cancer

Skin cancers and solar keratoses generally develop because of too much UV radiation from the sun and other sources such as solariums or sunlamps. Skin cancer is related to sunburn, particularly during childhood, as well as exposure to UV radiation over a number of years.

Each time your unprotected skin is exposed to UV radiation from the sun or other sources such as solariums, the UV radiation causes changes to take place in the structure of the cells. In particular, UV radiation damages your genes. Too much UV radiation causes the skin to become permanently damaged, and the damage will worsen as long as your skin is exposed to UV radiation.

UV radiation also decreases the ability of the immune system in the skin to recognise and attack newly forming skin cancer cells, making it easier for them to grow.

Skin cancer is one of the few almost totally preventable cancers. The most important years for sun protection are during childhood and adolescence. Sunburn and overexposure to UV radiation during these years greatly increase the chance of melanoma and other skin cancers later in life.

How common is skin cancer?

Over 380,000 Australians are treated for skin cancer every year. This is the highest rate in the world. In Australia, skin cancer is the most common type of cancer. Over 95% of skin cancers are cured if treated early.

Who is at risk?

Most Australians are at risk of skin cancer, but some are more at risk than others. They include people who:

are fair-skinned and don't tan but go red in the sun
have freckles or many moles
were exposed to Australia's sun as children
suntan or burn intentionally to make their skin appear browner
have a family history of skin cancer
work indoors, but get a lot of sun exposure every weekend
work outdoors for long periods of time
use sunlamps, sunbeds and solariums.

There is a greatly increased risk of squamous cell carcinoma if your immune system is lowered by drugs taken after an organ transplant.

Less common risk factors

If you take medicine that makes you more sensitive to sun exposure, take extra care to protect yourself. People who have received UV therapy for conditions such as psoriasis may also be at slightly higher risk. Ask your doctor if you are concerned about medicines you take. Other rare risk factors are over exposure - perhaps through heavy industrial use - to certain chemicals including coal tar, soot, pitch, asphalt, creosotes (coal or wood tar), paraffin waxes, petroleum derivatives and arsenic. Protective clothing should be worn if you handle these substances.