Squamous cell carcinoma

Squamous cell carcinoma

 

What is squamous cell carcinoma?

Squamous cell carcinoma is cancer that begins in the squamous cells, which are thin, flat cells that look like fish scales under the microscope. The word squamous came from the Latin squama, meaning "the scale of a fish or serpent" because of the appearance of the cells.

Squamous cells are found in the tissue that forms the surface of the skin, the lining of the hollow organs of the body, and the passages of the respiratory and digestive tracts. Thus, squamous cell carcinomas can actually arise in any of these tissues.

Squamous cell carcinoma of the skin occurs roughly one-quarter as often as basal cell carcinoma. Light-colored skin and a history of sun exposure are even more important in predisposing to this kind of cancer than to basal cell carcinoma. Men are affected more often than women. Patterns of dress and hairstyle may play a role. Women, whose hair generally covers their ears, develop squamous cell carcinomas far less often in this location than do men.

The earliest form of squamous cell carcinoma is called actinic (or solar) keratosis. Actinic keratoses appear as rough, red bumps on the scalp, face, ears, and backs of the hands. They often appear against a background of mottled, sun-damaged skin. They can be quite sore and tender, out of proportion to their appearance. In a patient with actinic keratoses, the rate at which one such keratosis may invade deeper in the skin to become a fully-developed squamous cell carcinoma is estimated to be in the range of 10%-20% over 10 years, though it may take less time. An actinic keratosis that becomes thicker and more tender raises the concern that it may have transformed into an invasive squamous cell carcinoma.

A rapidly-growing form of squamous cell carcinoma that forms a mound with a central crater is called a keratoacanthoma. While some consider this not a true cancer but instead a condition that takes care of itself, most pathologists consider it to be a form of squamous cell cancer and clinicians treat is accordingly.

Other forms of squamous cell carcinoma that have not yet invaded deeper into the skin include

·         actinic cheilitis, involving the lower lip with redness and scale, and blurring the border between the lip and the surrounding skin;

·         Bowen's disease, sometimes referred to as squamous cell carcinoma in situ. (The Latin words in situ refer to the presence of the cancer only in the superficial epidermis, without deeper involvement.) Bowen's disease appears as scaly patches on sun-exposed parts of the trunk and extremities; and

·         Bowenoid papulosis: These are genital warts that under the microscope look like Bowen's disease but behave like warts, not like cancers.

What are risk factors for developing squamous cell carcinoma?

The single most important factor in producing squamous cell carcinomas is sun exposure. Many such growths can develop from precancerous spots, called actinic or solar keratoses. These lesions appear after years of sun damage on parts of the body like the forehead and cheeks, as well as the backs of the hands. Sun damage takes many years to promote skin cancer. It is therefore common for people who stopped being "sun worshipers" in their 20s to develop precancerous or cancerous spots decades later.

Several rather uncommon factors may predispose to squamous cell carcinoma. These include exposure to arsenic, hydrocarbons, heat, or X-rays. Some squamous cell carcinomas arise in scar tissue. Suppression of the immune system by infection or drugs may also promote such growths. Some strains of HPV (the human papillomavirus responsible for causing genital warts) can promote development of squamous cell carcinoma in the anogenital region.

Can squamous cell carcinoma of the skin spread (metastasize)?

Yes. Unlike basal cell carcinomas, squamous cell carcinomas can metastasize, or spread to other parts of the body. These tumors usually begin as firm, skin-colored or red nodules. Squamous cell cancers that start out within solar keratoses or on sun-damaged skin are easier to cure and metastasize less often than those that develop in traumatic or radiation scars. One location particularly prone to metastatic spread is the lower lip. A proper diagnosis in this location is, therefore, especially important.

How is squamous cell carcinoma diagnosed?

As with basal cell carcinoma, doctors usually perform a biopsy to make a proper diagnosis. This involves taking a sample by injecting local anesthesia and punching out a small piece of skin using a circular punch blade. Usually the method used referred to as a punch biopsy. The skin that is removed is then examined under a microscope to check for cancer cells.

How is squamous cell carcinoma treated?

Techniques for treating squamous cell carcinoma are similar to those for basal cell carcinoma (for detailed descriptions, see above under treatment of basal cell carcinoma):

·         Curettage and desiccation: Dermatologists often prefer this method, which consists of scooping out the basal cell carcinoma by using a spoon like instrument called a curette. Desiccation is the additional application of an electric current to control bleeding and kill the remaining cancer cells. The skin heals without stitching. This technique is best suited for small cancers in non-crucial areas such as the trunk and extremities.

·         Surgical excision: The tumor is cut out and stitched up.

·         Radiation therapy: Doctors often use radiation treatments for skin cancer occurring in areas that are difficult to treat with surgery. Obtaining a good cosmetic result generally involves many treatment sessions, perhaps 25 to 30.

·         Cryosurgery: Some doctors trained in this technique achieve good results by freezing basal cell carcinomas. Typically, liquid nitrogen is applied to the growth to freeze and kill the abnormal cells.

·         Mohs micrographic surgery: Named for its pioneer, Dr. Frederic Mohs, this technique of removing skin cancer is better termed, "microscopically controlled excision." The surgeon meticulously removes a small piece of the tumor and examines it under the microscope during surgery. This sequence of cutting and microscopic examination is repeated in a painstaking fashion so that the basal cell carcinoma can be mapped and taken out without having to estimate or guess the width and depth of the lesion. This method removes as little of the healthy normal tissue as possible. Cure rate is very high, exceeding 98%. Mohs micrographic surgery is preferred for large basal cell carcinomas, those that recur after previous treatment, or lesions affecting parts of the body where experience shows that recurrence is common after treatment by other methods. Such body parts include the scalp, forehead, ears, and the corners of the nose. In cases where large amounts of tissue need to be removed, the Mohs surgeon sometimes works with a plastic (reconstructive) surgeon to achieve the best possible postsurgical appearance.

·         Medical therapy using creams that attack cancer cells (5-Fluorouracil--5-FU, Efudex, Fluoroplex) or stimulate the immune system (Aldara). These are applied several times a week for several weeks. They produce brisk inflammation and irritation. The advantages of this method is that it avoids surgery, lets the patient perform treatment at home, and may give a better cosmetic result. Disadvantages include discomfort, which may be severe, and a lower cure rate, which makes medical treatment unsuitable for treating most skin cancers on the face.

The possibility of metastasis makes it especially important to diagnose squamous cell carcinomas early and treat them adequately.

How is squamous cell carcinoma prevented?

Even more so than is the case with basal cell carcinoma, the key principles of prevention are minimizing sun exposure and getting regular checkups.

Common-sense preventive techniques are the same as for basal cell carcinoma and include

·         limiting recreational sun exposure;

·         avoiding unprotected exposure to the sun during peak radiation times (the hours surrounding noon);

·         wearing broad-brimmed hats and tightly-woven protective clothing while outdoors in the sun;

·         regularly using a waterproof or water-resistant sunscreen with UVA protection and SPF 30 or higher;

·         undergoing regular checkups and bringing any suspicious-looking or changing lesions to the attention of a doctor; and

·         avoiding the use of tanning beds and using a sunscreen with an SPF 30 and protection against UVA (long waves of ultraviolet light). Many people go out of their way to get an artificial tan before they leave for a sunny vacation, because they want to get a "base coat" to prevent sun damage. Even those who are capable of getting a tan, however, only get protection to the level of SPF 6, whereas the desired level is an SPF of 30. Those who only freckle get little or no protection at all from attempting to tan; they just increase sun damage. Sunscreen must be applied liberally and reapplied every two to three hours, especially after swimming or physical activity that promotes perspiration, which can weaken even sunscreens labeled as "waterproof."