Skin cancer is the most common type of cancer in the United States, with more than two million new cases diagnosed each year. Up to 50 percent of Americans who reach age 65 will have some type of skin cancer. It's also increasing in young people.
The skin is made up of three main layers: the epidermis (outer layer); the dermis (middle layer); and the subcutis (the deepest layer). The epidermis has three different types of cells: squamous cells form the top level; basal cells form the next layer; and the deepest layer contains melanocytes, cells that give skin its color. Skin cancers are caused when DNA of cells are damaged and the cells grow uncontrollably to form a tumor.
There are three major types of skin cancer. The names of the three types come from the type of skin cell in which they begin: basal cell carcinoma; squamous cell carcinoma; and melanoma. (Carcinoma is the name given to cancers that begin in cells that cover or line an organ.) Other skin cancers combined make up less than 1 percent of cases. These include Merkel cell carcinoma, adenexal tumors, various types of sarcomas, and cutaneous lymphomas.
This is the most common cancer, accounting for about 80 percent of diagnosed cases. Most BCCs are on skin that has extensive exposure to the sun, such as face, ears, scalp, and upper chest and back. These are slow-growing cancers that rarely spread (metastasize). Early diagnosis and treatment can prevent damage to areas around the cancer and metastasis. Usually, BCCs look like small, smooth, pearly or waxy bumps.
This is the second most common type, accounting for about 20 percent of cases. SCCs often come from spots that are dry, scaly, reddish-brown, yellowish-black, or normal skin color and are called actinic keratoses. Most SCCs are on areas of the skin that have had exposure to the sun, but they can be found on other areas, such as the mouth and genital area. The majority occur in fair-skinned and elderly people. SCCs can metastasize if not treated. Usually squamous cell cancers look like firm, red bumps, or rough, scaly flat areas that may itch, bleed, and form a crust.
Basal cell and squamous cell carcinomas can cause considerable damage and disfigurement if untreated. If detected and treated early, however, these carcinomas have a cure rate of more than 95 percent.
This form of skin cancer is least common, causing less than 5 percent of skin cancer cases. It begins in the melanocytes, the cells in the skin that give skin its color. This type of cancer usually develops in a mole or a spot that looks like a mole.
Malignant melanoma causes a large majority of all deaths from skin cancer. This disease can spread to the lymph system and other organs, most commonly the lungs, liver, and brain. Malignant melanoma diagnosed at an early stage usually can be cured, but melanoma diagnosed at a late stage is more likely to have spread and cause death.
Exposure to the sun's ultraviolet (UV) rays appears to be the most important environmental factor in the development of all three types of skin cancer. The sun's ultraviolet rays (UV) damage the DNA of skin cells.
Skin cancer is largely a preventable disease if you consistently follow protective practices and behaviors. UV rays from artificial sources of light, such as tanning beds and sun lamps are just as dangerous as those from the sun, and should be avoided.
UV light is further defined as either UVA or UVB. About 30 to 50 times more UVA rays reach the earth than UVB rays. UVA is present with about the same intensity during all daylight hours throughout the year, and these rays can go through clouds and glass. The highest amount of UVB hits the U.S. between 10 a.m. and 4 p.m. from April to October. These rays do not come through glass well, but they can damage skin year round.
UVA rays cause rapid tanning. These rays are present throughout the year and can penetrate deeply, reaching the dermis and the fat layer just below the skin. Exposure to UVA radiation over time causes damage to the connective tissue under the skin, leading to wrinkles.
UVB rays cause the most harm to skin. These rays are greatest during the summer, but snow and ice reflect UVB radiation, so excess exposure can occur in winter, too. UVB radiation delivers a high amount of energy to the outer layers of the epidermis. UVB is primarily responsible for sunburn, suntan, inflammation, and the changes in the DNA of skin cells that leads to skin cancer. It is most intense when the sun is directly overhead between 10 a.m. and 4 p.m.
The total amount of lifetime sun exposure is the cause of basal cell and squamous cell skin cancers. Severe sunburns, most often before age 18, can cause a melanoma later in life. Other causes can be frequent exposure to X-rays, having scars from burns or disease, and exposure to certain chemicals.
Although anyone can get skin cancer, people with certain risk factors are particularly at risk. These are risk factors for skin cancer:
Chronic exposure to the sun, or tanning lamps or booths
Light skin color
Family history of skin cancer
Personal history of skin cancer
Gender; males are twice as likely as females to have this cancer
Poor tanning ability and easily sunburned
Red or blonde hair, light-colored eyes, light skin color
Freckles, which indicate sun sensitivity and sun damage
Exposure to certain chemicals like arsenic, tar, and paraffin
Radiation treatment, which increases the risk for cancer in the skin over the treated area
People who smoke are at an increased risk of skin cancer, especially on the lips
Unusual moles, change in existing mole, new moles
Exposure to sunlight, especially severe sunburn before age 18
Using tanning booths
Family or personal history of melanoma
Red or blonde hair, light-colored eyes, light skin color
Gender; males have a higher risk
Suppressed immune system
Skin cancers can occur anywhere on the body, but most often are found on areas exposed to the sun.
The most common symptom is a new growth on the skin or a sore that does not heal in the usual time. The first sign of a melanoma is frequently a change in the shape, color, or size of an existing mole, or the appearance of a new mole. It is important to look for changes in existing moles and new moles. You can remember what type of changes to look for in an existing mole by remembering the ABCD rule:
Asymmetry: The shape of one half of the mole is different from the other half
Borders: The outside edges of the mole are ragged
Color: The mole has different shades of colors, such as brown, black, tan, red, or blue (although some can be white or have no color change)
Diameter: The size of the mole has changed
If you notice any of these changes in a mole or the growth of a new mole, or a mole begins to bleed or ooze fluid, see your health care provider. Skin cancer is diagnosed by a biopsy.
Treatment depends on the type of skin cancer and the extent to which it has spread. Basal and squamous skin cancers can be treated by:
Mohs surgery. This is a special type of surgery for skin cancer that shaves one layer of cancerous tissue at a time. The tissue is immediately checked under a microscope to see if it contains cancer cells. The layers are removed until no cancer cells are found in the shaved cells.
Curettage and electrodessication. In curettage, the cancer cells are scooped out using a special instrument called a curette. A special instrument applies an electric current to the area to stop bleeding and kill any cancer cells in the margin; this process is called electrodessication.
Cryosurgery. This freezes the cells with liquid nitrogen, killing abnormal cells.
Laser therapy. This uses a narrow beam of intense light to kill cancer cells.
Chemotherapy. This uses drugs to kill cancerous cells. The drugs can be given orally, injected, infused intravenously (in a vein), or put right on the skin.
Radiation. This uses high-energy rays (such as x-rays) or particles (such as photons, electrons, or protons) to kill cancer cells.
Melanomas can be treated by surgery, chemotherapy, radiation, and biologic therapy, which are treatments that help the body's immune system fight the cancer.
Your exposure to UV depends on the strength of the sunlight, which is determined by where you live; the length of exposure; and whether you protect your skin with sunscreen and clothing. The areas of the body that receive the most sun exposure over a lifetime are the face, back of the neck, bald head, upper chest, forearms, backs of the hands, and lower legs. You can tell how much sunlight has changed your skin by comparing the sun-exposed surfaces, such as the top of your forearm, with the inside of your forearm, which is usually protected from the sun.
Sun exposure adds up, so protecting yourself from too much exposure is important. People can take simple steps to plan ahead and protect themselves from the sun's UV rays. These options are important to remember year round and during all outdoor activities, and not just when at the beach or pool.
Covering up with clothing is the best protection. Up to 80 percent of non-melanoma skin cancers occur on the head and neck, so a wide-brimmed hat should be worn to shade the face, ears, scalp, and neck from the sun's UV rays. A hat with a four-inch brim provides the most protection. If a baseball cap is worn, sunscreen with a sun protection factor (SPF) of at least 30 should also be used to protect the ears and neck.
The best protection for the body is a long-sleeved shirt and long pants. Dark colors provide better protection than light colors. Wet fabric gives less protection than dry. Some clothing has SPF protection added; a typical shirt, however, has an SPF rating substantially lower than the recommended SPF 15, so it is wise to double up on protection by using sunscreen with at least SPF 30 and staying in the shade when possible.
Because the sun's UV rays are strongest and do the most damage during midday, outdoor activities should be avoided at this time. If this is not possible, then finding the shade of a tree, beach umbrella, or tent is a practical way to protect the skin.
There are two types of sunscreens:
Physical sunscreens, such as zinc or titanium oxide, contain particles that scatter and reflect sunlight from the skin.
Chemical sunscreens, which absorb radiation.
Sunscreens generally do a good job filtering out the UVB rays, which cause sunburn. But most sunscreens don't defend nearly as well against the UVA rays. That's true even for some products labeled ''broad-spectrum UVA/UVB protection."
SPF refers only to protection from UVB rays. SPF 15 blocks about 93 percent of UVB rays, and SPF 50, often more expensive, blocks about 98 percent. A higher SPF rating does not mean you can spend more time in the sun.
Experts say the best protection against UVA is a sunscreen that includes zinc oxide, titanium dioxide, oxybenzone, or avobenzone.
Most people do not apply enough of the sunscreen to get the full SPF rating. An adult should use enough sunscreen to fill a shot glass and use it to cover arms, legs, neck and face. If you are using insect repellant or other lotions, apply the sunscreen first.
For adults and children, sunscreens should be applied 20 to 30 minutes before exposure and every two hours afterward, as well as after swimming or sweating.
Babies younger than six months should be kept out of direct sunlight and protected from the sun using hats and protective clothing. Sunscreens should not be used on infants younger than six months, unless adequate clothing and shade are not available.
Use a lip balm with sunscreen to protect lips.
Sunglasses protect the tender skin around the eyes and reduce the risk for developing cataracts. Look for sunglasses that block both UVA and UVB rays. Wrap-around lenses are ideal because they keep UV rays from hitting the sides of the eyes.
© 2013 Main Line Health