Actinic Keratosis

(Precancerous Skin Lesion, Solar Keratosis)

The Facts

Actinic keratosis (AK) is a lesion that forms on sun-damaged skin. The lesions are small scaly patches on parts of the body, such as the face, ears, bald scalp, arms, and hands, which have been chronically exposed to the sun.

AK is a precancerous condition that affects only the top layer of skin (the epidermis). Ultraviolet (UV) rays from the sun damages the skin and if left untreated, 15% of AK can turn into a form of skin cancer called squamous cell carcinoma (SCC). This percentage increases significantly in people who have more than 5 AK lesions. When they are found early, AKs are highly treatable.

AK is more common in people with fair skin. About 60% of all Canadians over the age of 40 have at least one AK lesion. Australia has the highest rate of AK in the world.

The Causes

UV light from the sun and commercial tanning lamps or beds are the major causes of AK. UV light causes changes in the genetic material of the skin's cells. Changes in certain genes can cause cells to grow abnormally and form lesions.

Risk factors include:

age 40 and older – AK can happen at any age, but the risk increases with accumulated sun exposure
immunosuppression – the body's ability to recognize and fight abnormal cells are lowered in people with weak immune systems (e.g., as a result of taking organ transplant medications or chemotherapy, or having AIDS), so cells with gene changes are allowed to grow and form lesions
people with fair skin – also people who have red or blonde hair and those who tend to burn rather than tan develop AK more easily
sun exposure – people who work outdoors or have more exposure to the sun are at higher risk

Symptoms And Complications

AK lesions are small scaly patches that can be flat or slightly raised. They can range in colour from one's skin tone to a reddish-brown colour. They are about 3 mm to 10 mm across and may gradually enlarge. The skin around the lesions may show other signs of sun damage such as dark blotching, broken blood vessels, and a yellowish tinge.

Over time, AK lesions may become thicker and harder. Their colour may change from red to brown. Sometimes, a cone-shaped growth occurs above the skin surface at the site of the lesion. This is called a cutaneous horn.

The most common site for AK is the face, but it can occur anywhere on the body that has had long-term sun exposure, such as the arms, legs, and back of the hands. Sunbathers, for example, may develop AK on other parts of their bodies.

The most significant complication of AK is skin cancer. Once the AK lesion invades the lower layer of the skin (dermis), it is classified as squamous cell carcinoma (SCC), a form of cancer. If not treated, the cancer may spread to other areas of the body. Lesions that are more red, raised, and firmer than other AK lesions are more likely to become skin cancer. About 10% of all AK lesions will become cancerous if left untreated for too long.

Making A Diagnosis

AK can look similar to other skin conditions such as psoriasis or skin cancer. Your doctor can usually diagnose AK with a physical examination, but the most definitive way to make a diagnosis is to do a skin biopsy. A biopsy removes a small piece of tissue for testing. Biopsies may also be used to check lesions that have come back after treatment or that did not respond to treatment.

Treatment And Prevention

There are several options available for treating AK. Which one is best will depend on factors such as the size and location of the lesions, the number of lesions, and the person's overall health.

Cryotherapy uses a very cold substance, like liquid nitrogen, to freeze and kill the skin cells that make up the AK lesion. The liquid nitrogen is applied as a spray or with a swab. This treatment method is best for a small number of lesions. Topical medications (see below) may be used prior to cryotherapy to improve results.

Excision is surgical removal of the lesion using a sharp blade.

Electrodessication and curettage dries out the AK cells with an electric current and then scrapes them out using a curette (a sharp instrument). These procedures require a local anesthetic. Like cryotherapy, these are not practical for large numbers of lesions.

Topical medications (medications that are applied to the skin) can be used to treat actinic keratoses and superficial basal cell carcinoma (sBCC). Topical medications include 5-fluorouracil* (also known as fluorouracil or 5-FU) and imiquimod.

5-FU belongs to the group of medications known as topical antineoplastics. It works by interfering with cancer cell growth. It is applied to the skin in a thin layer and is then covered. The treatment is repeated daily over several weeks. This method is good for treating large areas of skin. Women who are pregnant should not use 5-FU.
Imiquimod is another topical medication for the treatment of AK. It belongs to a group of medications called immune response modifiers. This type of medication works by stimulating the immune system to produce substances that fight against the cancer. The treatment is applied to the skin twice a week for 16 weeks. This method is good for treating larger areas of skin.

Photodynamic therapy (PDT) uses light and a light-sensitizing medication to kill AK skin cells. The medication is applied to the skin and is absorbed by the abnormal AK cells more than the normal surrounding cells. The skin is then exposed to a specific colour of light that activates the medication and kills the cells. PDT is good for treating large areas of skin with many AK lesions.

Other possible treatments include:

chemical peels
dermabrasion
laser treatment
other topical medications (e.g., diclofenac)

The best way to prevent AK is to avoid overexposure to the sun. Use a sunscreen with a sun protection factor (SPF) of at least 30, applied one-half hour before sun exposure and reapply every 2 hours. Wear a hat and protective clothing to help protect your skin from the sun's UV rays. Remember to protect children as well. Try to stay out of the sun during peak hours (11 am to 4 pm). It's important to make sure your sunscreen protects against both UVA and UVB rays.