Squamous cell carcinoma (SCC) is a skin cancer. It arises from the uncontrolled growth of squamous cells in the epidermis, the outer layer of skin.
Sometimes this skin tumor is referred to as cutaneous squamous cell carcinoma (CSCC). This distinguishes it from squamous cell carcinomas that occur in other parts of the body.
Squamous cell carcinoma is the second most common skin cancer
Squamous cell carcinoma is the second most common type of skin cancer. There are over 1 million cases and more than 15,000 death occurring annually in the United States. Only basal cell carcinoma is more common.
Like basal cell carcinoma, SCCs are caused by long term exposure to ultraviolet radiation from sun exposure and indoor tanning devices.
Although SCCs may occur anywhere on the body, they most frequently develop in areas that have been exposed to the sun. These include:
- balding scalp
- back of the hands
The appearance of squamous cell carcinomas can vary
Squamous cell carcinomas often appear as a thick, rough, scaly patch that persists. It may occasionally bleed or develop a reoccurring crust.
SCC may appear like a wart with a rough surface or an inflamed scaly sore that does not heal.
The clinical course of squamous cell carcinoma
Although most patients who develop SCCs have localized disease that can be cured, tumor reoccurrence, tumor spread to other parts of the body, and death occasionally occurs.
Larger tumors may cause disfigurement as they may penetrate into the underlying tissues causing nerve or muscle damage. SCCs that have spread into the underlying tissue have been resistant to previous therapy or have reoccurred are considered “advanced” SCCs.
Risk factors for squamous cell carcinoma
The following are risk factors for squamous cell carcinoma:
- Fair-skinned individuals with blond or red hair, light-colored eyes, green, blue or gray
- A history of excessive exposure to UV radiation (sunlight or tanning beds)
- Older than 50 years of age
- Male gender
- History of basal cell carcinoma or other skin cancer
- Immunosuppression: including patients who have had an organ transplant, suffer from chronic leukemia, or those on immunosuppressive medication
- History of human papillomavirus infection
- Psoriasis patients
Staging of squamous cell carcinoma
Staging of squamous cell carcinomas is used to determine if, or how far, the cancer has spread. Treatment plans are determined by the stage or extent of disease.
Factors that determine the stage of an SCC include the size of the tumor, the depth of growth into the skin, and whether the tumor has spread to lymph nodes or other parts of the body.
The original tumor is limited to the most superficial layer of skin, the epidermis. This stage is also called squamous cell carcinoma in situ.
The tumor is less than or equal to 2 centimeters in width. Although it may have spread into the second layer of skin the dermis, it has not invaded underlying muscle, cartilage or bone. In addition, the tumor has not spread to lymph nodes or other parts of the body. No more than two high-risk features apply. (See below)
The tumor is larger than 2 centimeters and may have extended into the dermis. The tumor has not spread to the underlying muscle, cartilage or bone, to lymph nodes or to other parts of the body.
The cancer has spread to areas below the skin. It has invaded the muscle, bone, cartilage or local lymph nodes but it has not spread to other parts of the body.
The cancer can be of any size. It has spread to areas outside of the skin including distant organs like the brain or lungs. It may also have spread to local lymph nodes.
High-risk features of squamous cell carcinoma
High-risk features are characteristics of the tumor that increase the chances that the SCC reoccurs after initial treatment or spreads to other parts of the body.
- 2 mm thick or Clark level ≥ IV
- A tumor that grows around a nerve
- SCC located on the ear or lip
- Poorly or undifferentiated cells on pathology (Differentiation refers to how similar the cancer cells look like the normal tissue from which the cells are derived. Poorly and undifferentiated cells spread more quickly.)
Treatment of squamous cell carcinoma
Fortunately, most squamous cell carcinomas of the skin are found in their earlier stages where they can be cured utilizing local treatment methods, such as:
Electrodesiccation and curettage
The abnormal tissue is scraped off the skin with a curette, a sharp round-tipped blade on a handle. The area is heated with an electrode that stops the bleeding and destroys the abnormal cancer cells that remain on the edge of the wound. This procedure is repeated several times. It is the ideal treatment for small low-risk superficial SCCs especially those found on the trunk and extremities.
The cancer and underlying tissue, along with a margin of normal skin to assure complete removal, is excised with a scalpel. The specimen is sent for pathological evaluation to confirm that the cancer is completely removed. This treatment is ideal for SCCs found in areas of the body where tissue sparing is not critical.
Mohs Micrographic Surgery
Mohs surgery involves the removing of skin cancer tissue, layer by layer, examining each layer at the time of removal until no evidence of tumor exists. Although it is complicated and time-consuming, the procedure has the highest cure rates of all therapies for SCC.
It is best utilized for high-risk tumors, large or aggressive cancers, recurrent tumors, and for cancers that occur in cosmetically sensitive areas around the eyes, nose, lips, ears, fingers or genitals.
Radiation therapy is often used in addition to surgery for tumors that have perineural invasion (cancer cells surround or track along a nerve) or regional metastasis. This type of therapy may be used as a primary treatment for SCC when surgery is not an option.
Multiple anticancer drugs are used to shrink or kill cancerous cells and reduce the spread of SCC tumors.
Multiple topical skin products are available for precancerous lesions and early in situ SCCs:
- 5-fluorouracil is a topical antimetabolite anticancer drug that is approved for pre-cancerous skin lesions but is often utilized to treat small early cutaneous SCCs cancers.
- Imiquimod is approved by the FDA to treat genital warts, precancerous lesions. and superficial basal cell carcinoma. It is often used on early SCCs.
- Vitamin A derivatives (retinoids) have been used to both treat and prevent non-aggressive SCC.
Treatment of advanced squamous cell carcinoma
Advanced SCCs can become life-threatening. In rare cases, when the SCC has spread to local lymph nodes and to more distant organs of the body, treatment often involves surgery, radiation therapy, and/or chemotherapy.
The FDA recently approved an intravenous infusion drug, Cemiplimab. Cemiplimab is for patients with locally advanced SCC of the skin, metastatic cutaneous squamous cell carcinoma, or for patients where surgery or radiation is not an option. It is the only medication specifically indicated for patients with advanced cutaneous SCC in the United States.
Anti-cancer chemotherapy agents such as cisplatin, a platinum coordination compound that disrupts DNA synthesis, doxorubicin, and 5-fluorouracil may be used.
Prevention of squamous cell carcinoma
The American Academy of Dermatology makes the following recommendations to help reduce the chances of developing SCC:
- When possible, wear protective clothing, long-sleeved shirt, pant, wide-brimmed hats, and sunglasses to minimize direct sun exposure to the skin
- Seek shaded areas especially between 10 a.m. and 4 p.m. when the sun’s ultraviolet radiation is most intense
- Apply a broad-spectrum sunscreen with an SPF (sun protection factor) of 30 or higher on all exposed skin. The sunscreen should be applied liberally and reapplied every 2 hours or more if excessively sweating or swimming.
- Avoid tanning beds
- Perform regular self-skin exams and note any changing moles or other skin lesions.
- Seek medical attention should you discover a new or changing skin growth.
The bottom line
Squamous cell carcinomas can vary from small easily treated lesions that can have local therapy to, in rare instances, a serious life-threatening disease that may require surgery, radiation and/or chemotherapy.
As is true for all skin cancers, prevention, mainly avoidance of sun exposure, is the best medicine. You should routinely examine your skin and seek the opinion of a dermatologist should you find an unexplained or suspicious skin lesion.
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