Keratoacanthoma (KA) is a low-grade, or slow-growing, skin cancer tumor that looks like a tiny dome or crater. KA is benign despite its similarities to squamous cell carcinoma (SCC), or the abnormal growth of cancerous cells on the skin’s most outer layer. KA originates in the skin’s hair follicles and rarely spreads to other cells.
KA is commonly found on sun-exposed skin, such as skin on the:
Treatments typically involve surgery, radiotherapy, or injections. Many doctors will recommend surgery to remove KA because it looks similar to the cancerous SCC. While untreated KA will eventually heal on its own, untreated SCC can spread to your lymph nodes.
Overall, the outlook for KA is good, as it’s a benign tumor. Read on to learn about the causes, risks, and how to protect yourself from getting KA.
The symptoms of KA are visual and lasts two to three months. The look is often compared to a small volcano.
First, KA shows up as small, round bump. Then, it grows into a lesion or wound and reaches a size of between 1 and 2 centimeters within a few weeks. The wound looks like a dome with a plug made of brown keratin, which is the same material as hair and skin.
If the brown keratin comes out, the KA will look like a crater. When it heals, it’ll flatten and leave a scar.
The exact cause of KA is unknown. Some factors that may contribute to getting KA are:
- sun exposure
- contact with chemical carcinogens, or cancer-causing chemicals
- infection with some strains of a wart virus, such as human papillomavirus
- genetic factors
KA and SCC consist of very similar epidemiological features. This means they develop at similar rates and have common causes. This suggests exposure to sunlight causes KA, and one of the main causes of SCC is ultraviolet (UV) exposure.
Developing KA before the age of 20 is rare. People who have a higher risk of developing KA are people who:
- have prolonged sun exposure
- have naturally fair skin
- have compromised immune systems
- frequently use a tanning bed
- are over the age of 60
Men are also at a higher risk than women.
Genetics may play a factor too. People with immediate family members who’ve had some form of skin cancer are at a higher risk for developing multiple KA. One study also reported spontaneous growth of KA two to three months after skin cancer surgery.
Multiple KAs may show up as tumors that are 5 to 15 centimeters. It’s a non-melanoma skin cancer that rarely metastasizes, meaning it won’t spread to other areas of the body. But it can still be dangerous and should be treated by a doctor.
Many people with one KA lesion may develop more throughout their lifetime. But several rare conditions can cause multiple KAs to appear at once.
These conditions include:
|Grzybowski syndrome, or generalized eruptive KA||hundreds of KA-like lesions appear at one time on the body||unknown|
|Muir-Torre syndrome||KA tumors are present in association with internal cancer||inherited|
|Multiple self-healing squamous epitheliomas of Ferguson-Smith||recurring skin cancers, such as KA suddenly appear and often spontaneously regress, resulting in pitted scars||inherited, but rare|
If you notice a changing or growing colored patch on your skin, contact a doctor or dermatologist.
It’s possible for your doctor to diagnose KA by looking at it, but because of its strong resemblance to SCC, an invasive type of skin cancer, your doctor may prefer to do a biopsy.
This means your doctor will want to cut out the KA for examination. This process involves numbing the KA with a local anesthetic before removing enough of the lesion to test with a scalpel or razor. The sample is then evaluated to form a diagnosis.
KA will go away on its own, but this can take many months. Your doctor may recommend surgery or medication to remove KA.
Treatment options depend on the location of the lesion, the patient’s health history, and the size of the lesion. The most common treatment is a minor surgery, under a local anesthetic, to remove the tumor. This may require stitches, depending on the size of the KA.
Other treatments include:
- If you have cryosurgery, your doctor will freeze the lesion with liquid nitrogen to destroy it.
- If you have electrodesiccation and curettage, your doctor will scrap or burn off the growth.
- If you have Mohs’ microscopic surgery, your doctor will continue to take tiny pieces of skin until the lesion is completely removed. This treatment is most often used on the ears, nose, hands, and lips.
- Doctors use radiation treatment and X-ray therapy for people who are unable to have a surgical procedure for other health reasons.
Medications are used if you aren’t considered a good candidate for surgery. Doctors can prescribe drugs for people who have numerous lesions.
The medical treatments include:
- intralesional methotrexate
- injecting a folic acid that halts DNA synthesis and kills cancer cells
- intralesional 5-fluorouracil, which is an injection that blocks cancer cells from reproducing
- topical 5-fluorouracil
- bleomycin, which is an anti-tumor agent that blocks cell cycles
- a 25 percent solution of podophyllin
- oral acitretin, or chemical vitamin A
- oral isotretinoin (Accutane)
These medications can reduce the size and the number of lesions, making the removal treatments or surgeries easier and less invasive. They aren’t a substitute for actual surgery or other removal treatments. Ask your doctor about any side effects these medications may cause.
Home care involves treating the site of the tumor after it’s removed to help the skin in the area heal. Your doctor will provide you with specific instructions, including to keep the area dry and covered while it heals.
The treatment doesn’t stop completely after the lesion is removed. Once you’ve had KA, it’s common for it to reoccur, so you’ll want to regularly go to follow-up appointments with your dermatologist or primary care physician. Maintaining healthy habits to protect your skin from the sun can help prevent reoccurring lesions.
KA is curable and isn’t life-threatening. The majority of KA lesions will only cause cosmetic scars at their worst.
However, some may spread to lymph nodes if left untreated. If it spreads, the risks increase significantly with less than a 20 percent 10-year survival rate. If cancer spreads from one location to another, then there’s less than a 10 percent chance for a 10-year survival rate.
People who develop KA are at a higher risk for future episodes. If you’ve had a KA tumor or lesion, schedule regular visits with your doctor so you can quickly identify and treat KA growths at an early stage. The doctor you see can be a dermatologist or a doctor with experience examining the skin for skin cancer and lesions.
If you’re concerned about a lesion or unusual mole, make an appointment with your doctor. Similarly, if a spot suddenly changes form, color, or shape, or starts to itch or bleed, ask your doctor to check it.
You can take steps to prevent KA by protecting your skin from the sun. Staying out of the sun in the middle of the day can help reduce direct sun exposure. You’ll also want to avoid any artificial UV lights, such as those that come from tanning beds.
Wear clothing that covers large portions of your skin and sunscreen with at least an SPF of 30. You’ll want to make sure that your sunscreen blocks both UVA and UVB light.
You can also regularly examine your skin for new or growing moles or colored patches. If you’re concerned about KA, make regular appointments with your doctor or dermatologist so that they can detect and promptly remove any KA tumors.