- Risk Factors
- Common Sites
What is skin cancer?
Most skin cancers are locally destructive cancerous (malignant) growth of the skin. They originate from the cells of the epidermis, the superficial layer of the skin. Unlike cutaneous malignant melanoma, the vast majority of these sorts of skin cancers rarely spread to other parts of the body (metastasize) and become life-threatening.
There are three major types of skin cancer: (1) basal cell carcinoma (the most common), (2) squamous cell carcinoma (the second most common), which originate from skin cells, and (3) melanoma, which originates from the pigment-producing skin cells (melanocytes) but is less common, though more dangerous, than the first two varieties. Other rare forms of skin cancer include lymphomas, Merkel cell cancers, and cancers of other tissue in the skin, including sarcomas as well as hair and sweat gland tumors. In this article, we will only be reviewing the most common forms of cancers, basal cell carcinoma and squamous cell carcinoma.
What are the risk factors for skin cancer?
The most common risk factors for skin cancer are as follows.
- Ultraviolet light exposure, either from the sun or from tanning beds. Fair-skinned individuals, with hazel or blue eyes, and people with blond or red hair are particularly vulnerable. The problem is worse in areas of high elevation or near the equator where sunlight exposure is more intense.
- A chronically suppressed immune system (immunosuppression) from underlying diseases such as HIV/AIDS infection or cancer, or from some medications such as prednisone or chemotherapy
- Exposure to ionizing radiation (X-rays) or chemicals known to predispose to cancer such as arsenic
- Certain types of sexually acquired wart virus infections
- People who have a history of one skin cancer have a 20% chance of developing a second skin cancer in the next two years.
- Elderly patients have more skin cancers.
Is skin cancer hereditary?
Since most skin cancers are caused by ultraviolet light exposure, skin cancers are generally not considered to be inherited. But the fact that skin cancer is much more common among poorly pigmented individuals and that skin color is inherited does support the proposition that genetics are very important. There are some very rare genetic syndromes that result in an increased number of skin cancers in those affected.
What causes skin cancer?
Except in rare instances, most skin cancers arise from DNA mutations induced by ultraviolet light affecting cells of the epidermis. Many of these early cancers seem to be controlled by natural immune surveillance, which when compromised, may permit the development of masses of malignant cells that begin to grow into tumors.
What are the different types of skin cancer?
There are several different types of skin cancers:
- Basal cell carcinoma is the most common cancer in humans. Over 1 million new cases of basal cell carcinoma are diagnosed in the U.S. each year. There are several different types of basal cell carcinoma, including the superficial type, the least worrisome variety; the nodular type, the most common; and the morpheaform, the most challenging to treat because the tumors often grow into the surrounding tissue (infiltrate) without a well-defined border.
- Squamous cell carcinoma accounts for about 20% of all skin cancers but is more common in immunosuppressed people. In most instances, its biologic behavior is much like basal cell carcinoma with a small but significant chance of distant spread.
- Less common skin cancers include melanoma, Merkel cell carcinoma, atypical fibroxanthoma, cutaneous lymphoma, and dermatofibrosarcoma.
What are the signs and symptoms of skin cancer?
Most basal cell carcinomas have few if any symptoms. Squamous cell carcinomas may be painful. Both forms of skin cancer may appear as a sore that bleeds, oozes, crusts, or otherwise will not heal. They begin as a slowly growing bump on the skin that may bleed after minor trauma. Both kinds of skin cancers may have raised edges and a central ulceration.
Signs and symptoms of basal cell carcinomas include:
- Appearance of a shiny pink, red, pearly, or translucent bump
- Pink skin growths or lesions with raised borders that are crusted in the center
- Raised reddish patch of skin that may crust or itch, but is usually not painful
- A white, yellow, or waxy area with a poorly defined border that may resemble a scar
Signs and symptoms of squamous cell carcinomas include:
- Persistent, scaly red patches with irregular borders that may bleed easily
- Open sore that does not go away for weeks
- A raised growth with a rough surface that is indented in the middle
- A wart-like growth
Actinic keratoses (AK), also called solar keratoses, are scaly, crusty lesions caused by damage from ultraviolet light, often in the facial area, scalp, and backs of the hands. These are considered precancers because if untreated, up to 10% of actinic keratoses may develop into squamous cell carcinomas.
When is a mole dangerous or high risk for becoming a skin cancer?
Moles are almost always harmless and only very rarely turn into skin cancer. If a mole becomes cancerous, it would be a melanoma. There is a precancerous stage, called a dysplastic nevus, which is somewhat more irregular than a normal mole. An early sign of melanoma is noticing a difference in a mole: asymmetry, irregular border, color changes, increasing diameter, or other evolving changes may signify a mole is melanoma. Moles never become squamous cell carcinomas or basal cell carcinomas.
What are the most common sites where skin cancer develops?
Skin cancers typically arise in areas of the skin exposed to the sun repeatedly over many years such as on the face and nose, ears, back of the neck, and the bald area of the scalp. Less commonly, these tumors may appear at sites with only limited sun exposure such as the back, chest, or the extremities. However, skin cancer may occur anywhere on the skin.
How do physicians diagnose skin cancer?
A skin biopsy is usually used to confirm a suspicion of skin cancer. This is performed by numbing the area under the tumor with a local anesthetic such as lidocaine. A small portion of the tumor is sliced away and sent for examination by a pathologist, who looks at the tissue under a microscope and renders a diagnosis based on the characteristics of the tumor.
What is the staging for skin cancer?
There is no specific staging system for basal cell carcinoma. If the tumor is wider than 2 cm (about ¾ inch diameter), it is probably a more serious tumor. Basal cell carcinomas of the ears, nose, and eyelid may also be of more concern, regardless of the size.
There is a staging system for squamous cell carcinoma. Large tumors that are thicker than 2 mm, invade the nerve structures of the skin, occur on the ear, and have certain worrisome characteristics under the microscope are of more concern. If the tumor metastasizes to a site at some distance from the primary tumor, the cancer is likely to be a dangerous tumor.
What is the treatment for skin cancer?
There are several effective means of treating skin cancer. The choice of therapy depends on the location and size of the tumor, the microscopic characteristics of the cancer, and the general health of the patient.
- Topical medications: In the case of superficial basal cell carcinomas, some creams, gels, and solutions can be used, including imiquimod (Aldara), which works by stimulating the body's immune system causing it to produce interferon which attacks the cancer, and fluorouracil (5-FU), a chemotherapy drug. Some patients do not experience any side effects of these topical treatments, but others may have redness, inflammation, and irritation. A drawback of topical medications is that there is no tissue available to examine to determine if a tumor is removed completely.
- Destruction by electrodessication and curettage (EDC): The tumor area is numbed with a local anesthetic and is repeatedly scraped with a sharp instrument (curette), and the edge is then cauterized with an electric needle. The advantage of this method is that it is fast, easy, and relatively inexpensive. The disadvantages are that the scar is often somewhat unsightly, and the recurrence rate is as high as 15%.
- Surgical excision: The area around the tumor is numbed with a local anesthetic. A football-shaped portion of tissue including the tumor is then removed and then the wound edges are closed with sutures. For very big tumors, skin grafts or flaps are needed to close the defect. The advantages of this form of treatment are that there is a greater than 90% cure rate, the surgical specimen can be examined to be sure that the whole tumor is successfully removed, and the scar produced is usually more cosmetically acceptable than that of the EDC procedure. It is a more complicated procedure and is more expensive than EDC.
- Mohs micrographic surgery: The site is locally anesthetized and the surgeon removes the visible tumor with a small margin of normal tissue. The tissue is immediately evaluated under a microscope and areas that demonstrate residual microscopic tumor involvement are re-excised and the margins are re-examined. This cycle continues until no further tumor is seen. This more complicated and expensive option is the treatment of choice for tumors where normal tissue preservation is vital, where the tumor margins are poorly defined, in tumors that have been previously treated and have recurred, and in certain high-risk tumors.
- Radiation therapy: Ten to fifteen treatment sessions deliver a high dose of radiation to the tumor and a small surrounding skin area. This form of treatment is useful in those who are not candidates for any surgical procedure. The advantage of radiation therapy is that there is no cutting involved. The disadvantages of this expensive alternative are that the treated area cannot be tested to be sure the whole tumor is gone and radiation scars look worse over time. It is for this reason it is usually reserved for elderly patients.
- Other types of treatments for skin cancers include cryosurgery where tissue is destroyed by freezing, photodynamic therapy (PDT) in which medication and blue light is used to destroy the cancerous tissue, laser surgery to vaporize (ablate) the skin's top layer and destroy lesions, and oral medications vismodegib (Erivedge) and sonidegib (Odomzo).
What kinds of doctors treat skin cancer?
The main type of doctor who will treat skin cancer is a dermatologist. Your primary care physician or internist may first notice a sign of skin cancer, but will refer you to a dermatologist for further testing and treatment. You may also see an oncologist, which is a cancer specialist.
If you have surgical removal of a tumor, depending on how much skin is removed, you may see a plastic or reconstructive surgeon after the tumor removal to help restore the appearance of the skin, especially on the face.
What is the prognosis and survival rate for skin cancer?
The prognosis for nonmelanoma skin cancer is generally excellent. Both basal cell carcinoma and squamous cell carcinoma are highly curable. There are virtually no deaths from basal cell carcinoma and only rare deaths with squamous cell carcinoma skin cancers, mostly in immunosuppressed individuals. Depending on the method of treatment and the location and type of skin cancer, the likelihood of a recurrence of a previously treated skin cancer is as low as 1% to 2% for Mohs surgery and up to 10% to 15% for destruction by electrodessication and curettage.
Early detection of skin cancers can lead to better outcomes. Know your skin and if you have any moles or spots that are suspect, see a dermatologist for a skin cancer screening. Awareness is key in identifying and treating skin cancers early.
Is it possible to prevent skin cancer?
Many skin cancers can be prevented by avoiding triggers that cause tumors to develop. Prevention strategies include protection from the sun by the use of sunscreens, protective clothing, and avoidance of the sun during the peak hours of 9 a.m. to 3 p.m. Parents should ensure children are protected from the sun. Do not use tanning beds, which are a major cause of excess ultraviolet light exposure and a significant risk factor for skin cancer. The American Academy of Dermatology (AAD) has noted a dramatic rise in the numbers and cost of skin cancer. Furthermore, there has been an increase in the total number of skin cancers and that new breakthrough treatments for melanoma, although expensive, comprise only a small portion of the total cost of skin cancer treatment. Most skin cancers are treated cost efficiently by dermatologists in an office setting.
Sunscreen use and vitamin D
A major source of vitamin D comes from sunlight exposure, which leads to the production of the vitamin in the skin. Some argue sunscreens block out so much of the sun's rays that inadequate vitamin D synthesis results. In fact, very few people actually apply sunscreen to every inch of their exposed skin, so vitamin D synthesis does occur. There is no reason not to use sunscreens because of a fear of low vitamin D. If there is a concern, vitamin D can be obtained by eating leafy vegetables or taking an oral multivitamin supplement.
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Bichakjian, Christopher, et al. "Guidelines of Care for the Management of Basal Cell Carcinoma." J Am Acad Dermatol 2017: 1-19.
Rogers, Howard W., Martin A. Weinstock, Steven R. Feldman, and Brett M. ColdIron. "Incidence Estimate of Nonmelanoma Skin Cancer (Keratinocyte Carcinomas) in the US Population, 2012." JAMA Dermatol 151.10 (2015): 1081-1086.
Skin Cancer Foundation. "Actinic Keratoses (AK)." 2016.
Skin Cancer Foundation. "Basal Cell Carcinoma Treatment Options." 2016.
Skin Cancer Foundation. "Do You Know Your ABCDEs?" 2016.