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Keratoacanthoma

 

What are the aims of this leaflet?

This leaflet has been written to help you understand more about keratoacanthoma (KAs). It tells you what they are, what causes them, what can be done about them, and where you can find out more about them.

What are keratoacanthomas?

KAs are relatively common skin growths. They are unusual in that, though they are not cancerous, initially they behave and can look like one form of skin cancer (a squamous cell carcinoma). They grow quickly over the first few weeks but do not spread to other parts of the body. Indeed, if left alone, they will usually go away, although sometimes they may take as long as a year to do so.

What causes keratoacanthomas?

Their precise cause is not known. Factors that sometimes play a part include heavy sun exposure, contact with some chemicals such as tar, smoking, infection with some strains of wart virus, a suppressed immune system, and minor injuries to the skin.

KAs are more common in fair than in dark-skinned individuals, and in men than women. They are rare under the age of 20 and become more common with age.

Are keratoacanthomas hereditary?

Usually not, though multiple KAs are a part of a few rare inherited conditions.

What are the symptoms of a keratoacanthoma?

Usually there are none apart from embarrassment at their appearance, as they tend to come up on exposed skin.

What does a keratoacanthoma look like?

The first sign is a small round skin-coloured or slightly reddish bump. Sometimes people squeeze this as it looks rather like a pimple, but no pus comes out. As it grows, a KA takes up its characteristic appearance. The small bump becomes a firm, more raised and domed nodule, with a smooth surface and striking central horn or plug made of yellow or brown keratin (the material of which hair and the outermost layer of normal skin is made). If the plug comes out, a central crusted crater will remain, giving the KA the look of a ‘mini-volcano’. As a KA goes away, its central plug is lost and the bump flattens. Eventually only a puckered scar remains.

KAs pass through three stages. Over the first 2 or 3 months (the growth phase) they grow rapidly, usually reaching a final diameter of 1 or 2 cms. As there is a danger of confusion with skin cancer, you should consult your doctor as early as possible during this phase of growth. Next comes a phase, again often lasting 2 or 3 months, during which the KA stays much the same (the static phase). Finally, the KA will slowly go away (the phase of involution), sometimes leaving behind a depressed scar.

KAs crop up most often on the face, and less often on the backs of the hands and forearms. Usually they are single and surrounded by normal skin.

How will a keratoacanthoma be diagnosed?

The most important condition to rule out is one type of skin cancer – a squamous cell carcinoma. The treatment for both is removal, and the specimen will be sent to the laboratory – but the two conditions do look similar even under the microscope.

Can it be cured?

Yes, removal leads to cure.

How can a keratoacanthoma be treated?

If left alone, KAs will eventually go away without any treatment at all. However this can take many months. Most people do not want to keep any ugly bump, in an area that others can see, for as long as this – the more so as it may leave an ugly scar. Active treatment is usually best, and will lead to a better scar too.

One simple way is to scrape the KA off with a sharp spoon-like instrument (a curette) under a local anaesthetic, and then to touch the raw area left behind with a hot point (cautery). The specimen that has been scraped off can then be sent to the laboratory. This method is most suitable for small KAs that have been diagnosed firmly on clinical grounds.

If there is any doubt over the diagnosis, it is best for the bump to be cut out and the area to be closed with stitches. This provides a better specimen for the pathologist to look at. Occasionally small KAs are dealt with by freezing them with liquid nitrogen. A few very large ones may be treated with radiotherapy.

If there is any doubt about the diagnosis, follow-up will be arranged as for a squamous cell carcinoma.

What can I do?

If you have had a KA, you are at increased risk of developing skin cancer later on. You will be taught how to examine your own skin regularly with this in mind. Avoiding too much exposure to the sun is sensible but this does not mean that you can’t ever go on a sunny holiday again; it just means you need to be careful. You can achieve this by covering yourself up and using sun protection creams.

Use a high factor sunscreen (minimum sun protection factor 25) on areas you can’t cover. A broad spectrum one is the best, as it will block both types of ultraviolet radiation (UVA and UVB). Don’t use the sunscreen as an excuse to stay out in the sun or not to bother with protective clothing. Covering up is better than using a sunscreen. Seek shade whenever possible