Squamous cell cancer (SCC), also known as squamous cell carcinoma, is a type of cancer. It develops in squamous cells, which are the thin, flat cells that make up the outermost layer of your skin. Squamous cells are also found in other parts of your body such as your lungs, mucous membranes, digestive tract, and urinary tract.

SCC that forms in your skin is known as cutaneous SCC (cSCC). cSCC develops due to changes in the DNA of squamous cells, which causes them to multiply uncontrollably. It often forms on parts of your skin frequently exposed to sunlight like your face, neck, or arms.

Keep reading to learn more about this type of skin cancer, what it looks like, what causes it, and how it’s diagnosed and treated.

Cutaneous SCC (cSCC) is a cancer that develops in the squamous cells of your skin. According to the Skin Cancer Foundation, about 1.8 million people in the United States are diagnosed with cSCC each year. It’s the second most common type of skin cancer.

Although cSCC isn’t life threatening, it can become dangerous if it goes untreated. When treatment isn’t received quickly, the growths can increase in size and spread to other parts of your body, causing serious complications.

People with cSCC often develop scaly, red patches, open sores, or warty growths on their skin. These abnormal growths can develop anywhere, but they’re most often found in areas that receive the most exposure to ultraviolet (UV) radiation, either from sunlight or from tanning beds or lamps.

Oral SCC also makes up more than 90 percent of mouth cancers. Lung SCC makes up about 30 percent of a group of lung cancers called non-small cell lung cancer and about 25 percent of lung cancers overall.

Here are some examples of what squamous cell carcinoma can look like:

Your skin has multiple layers. The outer, protective layer of the skin is known as the epidermis. The epidermis has three main types of cells:

  • keratinocytes (skin cells, also called squamous cells)
  • melanocytes (pigment-producing cells)
  • Langerhans cells (immune cells)

The cells of the epidermis are constantly shedding to make way for fresh, new skin cells.

However, when certain genetic changes occur in the DNA of any of these cells, skin cancer can occur. The main types of skin cancer are:

Squamous cell cancer

Squamous cells are the cells closest to your skin’s surface, and their purpose is to line your skin. cSCC often develops in areas of the body that are frequently exposed to UV radiation, such as your face, hands, and ears.

Basal cell cancer

Basal cells sit below the squamous cells, and they’re constantly dividing to form new cells. According to the American Cancer Society, basal cell carcinoma makes up about 80 percent of skin cancers.

Like cSCC, basal cell cancer typically develops in areas exposed to UV rays, particularly your face and neck. This type of cancer tends to grow slowly, and it rarely spreads to other parts of your body.

However, if basal cell cancer goes untreated, it can eventually spread to your bones and other tissues.

Melanoma

Along with basal cells, melanocytes are located in the deepest section of your epidermis. These cells are responsible for producing melanin, the pigment that gives skin its color. When cancer develops in melanocytes, the condition is known as malignant melanoma.

Malignant melanoma is less common than squamous cell and basal cancers, but it’s more likely to grow and spread when it’s left untreated.

cSCC often occurs in areas exposed to UV radiation, such as your face, ears, and hands. However, it can also appear in your mouth, around your anus, and on your genitals.

Symptoms of cSCC can include:

  • an open sore that can have raised borders
  • a scaly, reddish patch of skin
  • a brown spot resembling an age spot
  • a wart-like growth
  • new growth on an old scar, birthmark, or mole
  • a horn-shaped growth
  • a firm and dome-shaped growth

According to the American Academy of Dermatology, cSCC is most commonly red or pink. It can also be:

  • brown
  • black
  • yellowish
  • white

In your mouth, this cancer can cause:

  • lip or mouth sores that don’t heal
  • sore or rough patches in your mouth
  • a loose tooth
  • white or reddish patches
  • painful swallowing
  • a growth inside your mouth

It’s a good idea to make an appointment with your doctor or dermatologist right away if you notice any symptoms of cSCC or experience a sore or growth that doesn’t heal. An early diagnosis and treatment are critical for preventing complications.

cSCC is caused by mutations that occur in squamous cell DNA. These changes cause abnormal cells to multiply out of control.

UV radiation is the most common cause of the DNA mutations that lead to cSCC and other skin cancers.

Causes of squamous cell cancer

Most cases of cSCC are attributed to exposure to UV radiation from sunlight or indoor tanning equipment like tanning lamps and beds. Other potential causes include:

  • Genetics. Genetic factors seem to play a role in the development of cSCC. A 2015 study found that people with a family history of cSCC are about four times more likely to develop it.
  • Smoking. People who smoke are more likely to develop cSCC, especially on their lips. Smoking is the primary risk factor for developing lung cSCC and other non-small cell lung cancers.
  • Chemical exposure. Exposure to certain chemicals such as coal tar, paraffin, some petroleum products, and arsenic may contribute to cSCC development.
  • Radiation exposure. Undergoing radiation therapy slightly increases your risk of developing skin cancer in the part of your body that received treatment.
  • Immunosuppression. Immunosuppression contributes to the development of cSCC. For example, organ transplant recipients have a 65 to 250 times higher risk of developing cSCC than people in the general population.
  • Severe burn scars and sores. cSCC can develop in severe burn scars, sores, or ulcers that have been on your body for many years.

Risk factors for squamous cell cancer

Risk factors for cSCC include:

  • having fair skin
  • having light-colored hair and blue, green, or gray eyes
  • having long-term exposure to UV radiation
  • living in sunny regions or at a high altitude
  • having a history of multiple severe sunburns, especially if they occurred early in life
  • having a history of being exposed to chemicals, such as arsenic
  • having a history of immunosuppression
  • history of severe burn scars, ulcers, or sores

Treatment for cSCC varies. Treatment is based on:

  • the extent and severity of your cancer
  • your age
  • your overall health
  • the location of the cancer

If cSCC is caught early, the condition can usually be successfully treated. It becomes harder to cure once it has spread. Many treatments can be performed as in-office procedures. Treatments may include:

  • Mohs micrographic surgery. In Mohs surgery, your doctor uses a scalpel to remove the abnormal skin and some of the surrounding tissue. The sample is immediately examined under a microscope. If there are any cancer cells in the sample, the process is repeated until no cancer cells are found.
  • Excisional surgery. During excisional surgery, your doctor removes the cancer cells as well as a thin layer of healthy skin in the surrounding area. Stitches are used to close the wound. The sample is then sent to a laboratory to ensure the entire cancerous area has been removed.
  • Electrosurgery. Also called electrodesiccation and curettage, electrosurgery involves scraping off the cancer and burning the skin to kill cancer cells. This process is typically done more than once to ensure thorough treatment and complete removal of the cancer.
  • Cryosurgery. During cryosurgery, your doctor uses liquid nitrogen to freeze and destroy the cancerous tissue. Like electrosurgery, this treatment is repeated multiple times to make sure all cancerous tissue has been eliminated.
  • Radiation. With radiation, high energy X-rays kill cancer cells. This treatment is administered externally by a machine, which aims the rays at the affected area. Radiation is often performed multiple times a week for several weeks.
  • Photodynamic therapy. Also known as PDT, photodynamic therapy involves the application of a photosensitizing substance to the cancerous areas. After 1 to 3 hours or longer, the areas that were medicated are exposed to strong light for several minutes. This activates the medication that was applied and kills abnormal cells.
  • Systemic drugs. Several types of systemic drugs are FDA approved to treat cSCC, including cemiplimab-rwlc (Libtayo) and pembrolizumab (Keytruda). Systemic drugs act on your whole body and are often used for aggressive cSCC.

Non-FDA-approved methods for treating squamous cell carcinoma

Some doctors may also use laser surgery and topical medications to treat cSCC. However, the Food and Drug Administration has not approved these methods for treating cSCC:

  • Laser surgery. During laser surgery, your doctor uses a concentrated beam of light to remove areas of skin that are abnormal.
  • Topical medications. Medications, such as 5-fluorouracil and imiquimod, that are applied on the skin to treat other skin cancers may also help treat cSCC.

Once cSCC has been treated, it’s critical to attend all follow-up visits with your doctor. cSCC can return, and it’s important to monitor your skin for any precancerous or cancerous areas at least once per month.

Your doctor will first perform a physical exam and inspect any abnormal areas for signs of cSCC. They’ll also ask you about your medical history. If cSCC is suspected, your doctor may decide to take a biopsy to confirm the diagnosis.

A biopsy usually involves removing a very small portion of the affected skin. The skin sample is then sent to a laboratory for testing.

In some cases, your doctor may need to remove a larger part or all of the abnormal growth for testing. Talk with your doctor about any potential scarring or biopsy concerns.

After receiving treatment for cSCC, be sure to attend all follow-up visits with your doctor. It’s possible for the cancer to return, so it’s critical to check your skin for any signs of cancer or precancer at least once per month.

To help reduce your risk of cSCC, follow these tips when possible:

  • Limit your sun exposure.
  • Avoid the sun during the hottest part of the day, which is between 10 a.m. and 4 p.m.
  • Wear sunscreen that has an SPF of at least 30 whenever you go out in the sun.
  • Wear sunglasses with UV ray protection.
  • Wear a hat and cover your skin when working outside.
  • Avoid using tanning beds and lamps.
  • Protect your skin during winter as well because winter UV rays can be especially dangerous.
  • Check your skin each month for any new or abnormal growths.
  • See a dermatologist once per year for a full-body skin check.

Early detection of cSCC is key to successful treatment. If cSCC isn’t treated in its early stages, the cancer may spread to other areas of the body, including the lymph nodes and organs. Once this occurs, the condition can be life threatening.

People with weakened immune systems due to certain medical conditions, such as HIV, AIDS, or leukemia, have a greater risk of developing more serious forms of cSCC.

It’s a good idea to see a doctor right away if you suspect you have any type of skin cancer.