What is a keratoacanthoma?
A keratoacanthoma is a benign, fast-growing, dome-shaped small tumour of the skin that occurs fairly commonly.
What does it look like?
The tumour is usually skin-coloured, smooth and hemispherical, and generally shows a central crater. Typically this crater is filled with a horny plug. The tumour can have a diameter varying from a few millimetres to a few centimetres.
How does it develop?
The cause is not entirely clear. A virus infection is probably involved in the development of the tumour. Sunlight also plays a role: keratoacanthomas are usually found on the sun-exposed parts of the skin (face, backs of the hands, ears). It is mainly people of middle age and older who develop keratoacanthomas, especially when they have had a lot of sun exposure in the past.
How is a keratoacanthoma distinguished from a squamous cell carcinoma?
Squamous cell carcinomas (malignant) can look exactly the same as keratoacanthomas (benign). To make it even harder, the tissue of the two conditions under the microscope is almost indistinguishable. In fact the difference in the speed at which the lesions develop is the only real guide the doctor has to tell them apart. Most dermatologists use a limit of 6 weeks: if the lesion has developed in less than 6 weeks and has grown very quickly, it is probably a keratoacanthoma; if the tumour has needed more time to grow, the chance is greater that it is a squamous cell carcinoma. In case of doubt, complete surgical removal of the lesion is always chosen.
How is it treated?
Excision. The keratoacanthoma can be cut out completely. This is done especially when there is doubt about the diagnosis and the possibility of a squamous cell carcinoma is considered. Since this doubt is often present, surgical removal in this way is usually the first choice.
When the dermatologist considers the chance of skin cancer to be very small, they may, in consultation with the patient, decide on one of the following treatments:
Curettage. The tumour is “scooped out” with a small, very sharp loop. Afterwards the base of the resulting pit is sometimes cauterised to reduce the chance of the keratoacanthoma returning.
Freezing. Keratoacanthomas can also be treated by dabbing with liquid nitrogen.
A keratoacanthoma can also disappear by itself, without treatment, but this often leaves ugly scars.
What is the outlook?
When a keratoacanthoma is only curetted, there is a chance that it grows again. When this happens repeatedly, surgical removal is usually the only option.
When to see a doctor
See your GP or a dermatologist promptly for any firm lump that appears and grows quickly over a few weeks, especially on sun-exposed skin, or a spot with a central crater or horny plug. Because a keratoacanthoma can be difficult to distinguish from a squamous cell carcinoma, early assessment — and usually removal — is important.