Squamous Cell Carcinoma – Causes, Incidence, and Risk Factors

Squamous cell cancer may occur in normal skin or in skin that has been injured or inflamed. Most skin cancers occur on skin that is regularly exposed to sunlight or other ultraviolet radiation.

The earliest form of squamous cell skin cancer is called Bowen’s disease (or squamous cell in-situ). This type of squamous cell carcinoma is in the epidermis (top layer of the skin) and has not yet invaded into the dermis (deeper layer of skin).

Squamous cell carcinoma is the 2nd most common type of skin cancer. Each year in the United States, over 250,000 cases of invasive squamous cell carcinomas are diagnosed. About 65% of squamous cell carcinomas occur on the head and neck. Currently it is estimated that 1 in every 5 Americans will develop a skin cancer during their lifetime; many of which are squamous cell carcinoma.

Actinic Keratosis is a precancerous skin lesion that may become a squamous cell cancer if left untreated. Approximately 10% of actinic keratosis will develop into a squamous cell carcinoma if not treated.

Risks for squamous cell skin cancer include:

  • Having light-colored skin, blue or green eyes, and blond or red hair
  • Long-term, daily sun exposure (such as in people who work outside)
  • Older age
  • Radiation exposure
  • Chemical exposure
  • Burns or large scars


Squamous cell skin cancer usually occurs on the face, ears, neck, hands, or arms, although it may occur in other locations as well.

The main symptom is a growing bump that may have a rough, scaly surface and flat reddish patches.

The earliest form appears as a scaly, crusted, reddish patch.

A sore that does not heal, bleeds, or is painful can be a sign of squamous cell cancer. Any change in an existing wart, mole, or other skin lesion could be a sign of skin cancer.

Diagnosis and Tests

Your doctor will check your skin and look at the size, shape, color, and texture of any suspicious areas.

If your doctor thinks you might have skin cancer, a piece of skin will be removed and sent to a lab for examination under a microscope. This is called a skin biopsy. There are different types of skin biopsies.

High Risk features of squamous cell carcinoma include: size less than 2cm, depth of invasion greater than 2mm, location on the lip or ear, developing within a scar, invasion into superficial nerves in the skin, and invasion into the deeper levels of the skin and fat.


A skin biopsy must be done to confirm a diagnosis of squamous cell skin cancer or other skin cancers.


Treatment depends on the size and location of the skin cancer, how far it has spread, and your overall health. Some squamous cell skin cancers may be more difficult to treat.

Treatment may involve:

  • Excision—cutting out the visible skin cancer with a safety margin of normal skin surrounding and stitching the skin together
  • Mohs surgery—removing the skin cancer and a thin layer of surrounding skin and looking at it immediately under a microscope. If any cancer is remaining, then additional layers of skin are removed until there are no signs of the cancer. Mohs surgery is usually used for cancers that are on the face, hands or other cosmetically sensitive areas, for large or aggressive cancers, or cancers in high risk patients.
  • Curettage and electrodesiccation—scraping away cancer cells and using electricity to kill any that remain; it is used to treat cancers that are not very large or deep
  • Cryosurgery—freezing the cancer cells with liquid nitrogen
  • Medication—skin creams containing imiquimod or 5-fluorouracil may be prescribed by your doctor for squamous cell carcinoma in-situ
  • Photodynamic therapy—treatment using a topical medication and high powered blue or red light to activate the medication can be used to treat squamous cell carcinoma in-situ
  • Radiation may be used if the squamous cell skin cancer has spread to organs or lymph nodes, or for cases that cannot be treated with surgery

 Expectations (Prognosis)

How well a patient does depends on many things, including how quickly the cancer was diagnosed. Most of these cancers are cured when diagnosed and treated early.

Some squamous cell cancers may return even after having appropriate treatment.

Patients who have a history of skin cancer have a higher risk of developing new skin cancers in other locations

If you have had skin cancer you should have regular check-ups so that a doctor can examine your skin. You should also examine your skin once a month. Use a mirror to check hard-to-see places, and call your doctor if you notice anything unusual.


If left untreated, squamous cell cancer will eventually spread to other parts of the body. In most patients, it takes many years for the cancer to spread.

Calling your Health Care Provider

Call for an appointment with your health care provider if you have a sore or spot on your skin that changes in:

  • Appearance
  • Color
  • Size
  • Texture

You should also call if an existing spot becomes painful or swollen, or if it starts to bleed or itch.


The best way to prevent skin cancer is to reduce your exposure to sunlight. Ultraviolet light is most intense between 10 a.m. and 4 p.m., so try to avoid sun exposure during these hours. Protect your skin by wearing full brim hats, long-sleeved shirts, and long skirts or pants.

Always use sunscreen:

  • Apply sunscreens with sun protection factor (SPF) ratings of at least 30, even when you are only going outdoors for a short time.
  • Apply a large amount of sunscreen on all exposed areas
  • Look for broad spectrum sunscreens that block both UVA and UVB light.
  • Use a waterproof formula
  • Apply sunscreen at least 30 minutes before going outside, and reapply it frequently, especially after swimming.
  • Remember to wear sunscreen even on cloudy days and in the winter

Other important facts to help you avoid too much sun exposure:

  • Be extra careful around surfaces that reflect light, such as water, sand, concrete, and white-painted areas.
  • Skin burns faster at higher altitudes.
  • Avoid sun lamps, tanning beds, and tanning salons


Soyer HP, Rigel DS, Wurm EM. “Actinic Keratosis, Basal Cell Carcinoma, Squamous Cell Carcinoma.” In: Bolognia JL, et al (eds.) Dermatology, 3rd Edition. Elsevier, Philadelphia. 2012. Pp 1777-1783.