Understanding skin cancer - the basics

What is skin cancer?

Skin cancers involve abnormal cell changes in the outer layer of skin called the epidermis.

It is by far the most common cancer in the world. Most cases are cured, but the disease is a major health concern because it affects so many people. The incidence of skin cancer is rising, even though most cases can be prevented by limiting the skin's exposure to ultraviolet radiation.

Skin cancer is about three times more common in men than in women, and the risk increases with age. Most people diagnosed with skin cancer are between 40 and 60 years old, although all forms of the disease are appearing more often in younger people. If you or any close relatives have had skin cancer, you are more likely to get the disease.

Every malignant skin tumour in time becomes visible on the skin's surface, making skin cancer the only type of cancer that is almost always detectable in its early, curable stages. Prompt detection and treatment of skin cancer is equivalent to cure.

Types of skin cancer

Skin cancers fall into two major categories: melanoma and non-melanoma.

Melanoma can start in heavily pigmented tissue such as a mole or birthmark as well as in normally pigmented skin. Melanoma usually appears first on the torso or back, although it can arise on the palm of the hand, on the sole of the foot, under a fingernail or toenail, in the mucous linings of the mouth, vagina or anus, and even in the eye.

Melanoma is an extremely aggressive, life-threatening cancer. It is readily detectable and usually curable if treated early, but it progresses faster than other types of skin cancer and tends to spread beyond the skin to affect the bones or brain. Once this occurs, melanoma becomes very difficult to treat and cure.

The two most common skin cancers, basal cell carcinoma and squamous cell carcinoma, are non-melanomas, which are rarely life-threatening. They progress slowly, seldom spread beyond the skin, are detected easily and usually are curable. Basal cell carcinoma, which accounts for nearly three out of four skin cancers, is the slowest growing. Squamous cell carcinoma is somewhat more aggressive and more inclined to spread. There are also a few rare non-melanomas such as Kaposi's sarcoma, a potentially life-threatening disease characterised by purple growths and associated with a suppressed immune system - it is almost always seen in patients with AIDS.

Some technically non-cancerous skin growths have the potential to become cancerous. The most common are actinic keratoses - crusty reddish lesions that may scratch off but grow back on sun-exposed skin. Another precancerous skin growth, cutaneous horns, appear as funnel-shaped growths that extend from a red base on the skin.