Updated May 15, 2014.

Squamous cell carcinomas (SCC) are the second most common form of skin cancer in the United States.  This article will discuss what squamous cell carcinomas are, how they are diagnosed, how they are treated, and what you can do to prevent them.

What is a squamous cell carcinoma of the skin?

Squamous cell carcinomas of the skin are the second most common type of skin cancer in the United States.  They result from uncontrolled excess growth of the cells called keratinocytes in the epidermis, which is the top layer of the skin.

What is the difference between an actinic keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma?

Actinic keratoses are precancerous growths in the skin.  They are rough reddish areas that occur most frequently on the parts of the body that receive the most direct sun exposure.  Actinic keratoses are caused by damage from the ultraviolet rays of the sun.  If left untreated, a fraction of actinic keratoses can progress to squamous cell carcinomas.

Squamous cell carcinoma in situ (SCCIS) is similar to a squamous cell carcinoma, but it has not grown down into the dermis, the layer of skin beneath the epidermis.  Squamous cell carcinoma in situ becomes squamous cell carcinoma when it grows downward into the dermis.

How do squamous cell carcinomas of the skin present?

Squamous cell carcinomas can present as red bumps or plaques on the skin. Often, they are rough and scaly. However, they can also be ulcerated with broken skin, crusty, bloody, or look like warts. 

How are squamous cell carcinomas diagnosed?

The diagnosis of squamous cell carcinomas, like other skin cancers, is confirmed by skin biopsy.  This involves cutting off a small sample of skin to be examined under the microscope by a pathologist.  While the appearance of the growth to the naked eye can strongly suggest squamous cell carcinoma to an expert, the only way to definitively make the diagnosis is with a biopsy.

How are squamous cell carcinomas treated?

There are various effective treatments for squamous cell carcinomas.  Squamous cell carcinomas can be surgically removed (excised) by a procedure called a skin cancer excision.  This involves cutting out the abnormal appearing skin with a surrounding rim of normal skin.  As with the biopsy, the removed skin is examined under the microscope to ensure that all of the squamous cell carcinoma has been removed.  If examination under the microscope indicates that there are cancer cells left behind, an additional procedure may be necessary.  A special type of surgery, called Mohs surgery, may also be used to treat squamous cell carcinomas.  This involves removing many thin layers of skin and examining them under the microscope to look for cancer cells.  Mohs surgery is often used for skin cancers on the head and neck and for other special cases. 

Less frequently, some squamous cell carcinomas cannot easily be treated surgically and require radiation therapy and/or chemotherapy.

Other less common therapies for squamous cell carcinoma include photodynamic therapy, which involves having a medicine painted over the area and then exposure to a therapeutic light, and laser therapy.  However, these are usually only appropriate for very early squamous cell carcinomas.

How can squamous cell carcinomas be prevented?

The most important aspect of preventing squamous cell carcinomas is sun protection.  Broad spectrum sun screen (with protection against UV-A and UV-B rays) with an SPF of 30 or greater should be used on all sun exposed parts of the body.  Sun screen should be reapplied frequently and after swimming or heavy sweating, even if water-resistant sun screen is used.  Sun screen use on the face on an everyday basis has been shown to decrease the effects of skin aging (such as wrinkles) and decreases the risk of all skin cancers.  Protective clothing, such as long sleeve shirts, long pants, sun glasses, and wide brimmed hats should also be worn in the sun.  The risk of squamous cell carcinomas can also be prevented by avoiding sun exposure between approximately 10 a.m. and 2 p.m., when the sun is the strongest.  Avoiding the use of tanning beds is important in preventing all skin cancers, including squamous cell carcinoma.

What is the difference between squamous cell carcinomas and basal cell carcinomas?

Basal cell carcinomas are a different type of skin cancer from squamous cell carcinomas.  In basal cell carcinomas, the cancerous cells originate from the deepest part of the epidermis called the basal layer, whereas squamous cell carcinoma cells originate from a different group of cells.  Basal cell carcinomas are the most common form of skin cancer and the most common cancer in the United States.  While many of the risk factors and treatments of basal and squamous cell carcinomas are similar, they are comprised of different cells and are therefore different cancers.

Sources:

Alam M, Ratner D. “Cutaneous Squamous-Cell Carcinoma.” New England Journal of Medicine, 2001;344(13):976-83.

Firnhaber JM. “Diagnosis and Treatment of Basal Cell and Squamous Cell Carcinoma.” American Family Physician, 2012;86(2):161-8.

Kim RH, Armstrong AW. “Nonmelanoma Skin Cancer.” Dermatology Clinics, 2012;30:125-39.

Hughes MCB, Williams GM, Baker P, Green AC. “Sunscreen and Prevention of Skin Aging: A Randomized Trial.” Annals of Internal Medicine, 2013;158(11):781-90.

“Squamous Cell Carcinoma.” American Academy of Dermatology. http://www.aad.org/dermatology-a-to-z/diseases-and-treatments/q---t/squamous-cell-carcinoma “Squamous Cell Carcinoma.”

Skin Cancer Foundation. http://www.skincancer.org/skin-cancer-information/squamous-cell-carcinoma

“Skin Cancer: Basal and Squamous Cell.” American Cancer Society. http://www.cancer.org/cancer/skincancer-basalandsquamouscell/detailedguide/skin-cancer-basal-and-squamous-cell-what-is-basal-and-squamous-cell