Skin cancer is the most common type of cancer, with more than 3 million cases diagnosed in the US each year. If found early, skin cancer can usually be cured and is responsible for less than 1 percent of all cancer deaths.
Forms of skin cancer
Basal cell carcinoma accounts for about 80 percent of skin cancers. It usually develops on the head and neck, although it can be found anywhere on the skin. It is mainly caused by sun exposure or develops in people who received radiation therapy as children. This type of skin cancer usually grows slowly and rarely spreads to other parts of the body.
Squamous cell carcinoma accounts for about 20 percent of skin cancers. It is mainly caused by sun exposure, so it may be diagnosed on many regions of the skin. Skin that has been burned, damaged by chemicals, or exposed to X-rays may also develop this cancer. Squamous cell carcinoma is commonly found on the lips; at sites of a long-standing scar; and on the skin outside the mouth, anus, and a woman’s vagina. About 2 to 5 percent of squamous cell carcinomas spread to other parts of the body.
Merkel cell cancer (also called neuroendocrine carcinoma of the skin or trabecular cancer) is rare and highly aggressive. It begins in hormone-producing cells just beneath the skin and in the hair follicles and is usually found in the head and neck region.
Melanoma is one of the most serious forms of skin cancer. It can grow deep into the skin, called invasive melanoma. It can also invade lymph nodes and blood vessels and spread to distant parts of the body, called metastatic melanoma. This form of skin cancer can develop anywhere on the body, including the head and neck, the skin under the fingernails, the genitals, and even the soles of the feet or palms of the hands.
Additional, rare types of skin cancer include Karposi sarcoma, various other sarcomas, cutaneous (skin) lymphoma, and skin adnexal tumors.
Risk factors for skin cancer
Sun exposure — Exposure to ultraviolet (UV) radiation from the sun plays a major role in skin cancer development. Skin cancer risk is higher for people who live at high altitudes or in areas with bright sunlight year-round, and who spend a lot of time outside during the midday hours. Recreational suntanning also increases risk. Although ultraviolet type B (UVB) radiation exposure appears to be more closely linked with skin cancer, newer research suggests that ultraviolet type A (UVA) may also play a role.
Artificial tanning — People who use tanning beds, tanning parlors, or sun lamps have an increased risk of developing all types of skin cancer. There is no safe amount of indoor tanning, and greater use increases the risk.
Fair skin — People with a fair complexion, blond or red hair, blue eyes, and freckles, or whose skin tends to burn rather than tan, have a higher risk of developing skin cancer. People with albinism, an inherited lack of skin pigment, have a high skin cancer risk.
Race/ethnicity — A person of any race or ethnicity can develop skin cancer. Melanoma rates are about 20 times higher in white people than in African-Americans. White people are also most likely to develop Merkel cell cancer, but some African-Americans and people of Polynesian descent also develop the disease.
Gender— The number of older white men and younger white women who have developed skin cancer has increased in recent years. Men are more likely than women to develop basal and squamous cell skin cancers. Men are also more likely to develop Merkel cell cancer. In the US, melanoma risk varies by age. Before age 50, the risk is higher for women; after age 50, the risk is higher for men.
Age — Most basal cell and squamous cell carcinomas typically appear after age 50 and risk rises with increasing age. In recent years, the number of skin cancers in people age 65 and older has increased dramatically, but this may be due to better screening and monitoring. Younger people can also develop non-melanoma skin cancer, especially if they have fair skin, an inherited (genetic) syndrome that puts them at high risk, or exposure to significant amounts of radiation or UV radiation from the sun. About half of people with melanoma are diagnosed when they are younger than 50 years old (melanoma is one of the most common cancers in people younger than 30, especially younger women), and about half when they are older than 50. Merkel cell cancer is most common in people older than age 70.
Precancerous skin conditions — Actinic keratoses (also called Bowen’s disease) can change into squamous cell cancers and appear as rough, red, or brown scaly patches on the skin. They are usually more common in areas exposed to the sun, and the greater their number, the higher the risk.
Long-term skin damage — Skin that has been burned, sunburned, or injured from disease (such as severe inflammatory skin diseases or skin over serious bone infections) has a higher risk of skin cancer.
Previous skin cancer — People who have had any form of skin cancer have a higher risk of developing another skin cancer. Among people diagnosed with one basal cell carcinoma, 35 to 50 percent will develop a new skin cancer within five years. People who have had basal or squamous cell skin cancers are also at increased risk of getting melanoma.
Smoking — People who smoke are more likely to develop squamous cell skin cancer, especially on the lips.
Exposure to certain chemicals — Arsenic exposure increases the risk of developing skin cancer. Workers exposed to coal tar, paraffin, and certain types of oil may also have an increased risk of skin cancer.
Previous treatment with radiation therapy — People who have had radiation treatment have a higher risk of developing basal cell carcinoma in the area that received the treatment. This risk increases over time, especially after 10 to 20 years. Children who receive radiation therapy are at six times the risk for basal cell carcinoma.
Weakened immune system — People who have weakened immune systems or who use certain medications that suppress immune function have a higher risk of developing skin cancer, including melanoma. This includes people who received stem cell or organ transplants and who take medication to stop organ rejection, people who take large doses of corticosteroids, and people with diseases such as HIV/AIDS and certain types of leukemia. Skin cancers in people with weakened immune systems tend to grow faster and are more likely to be fatal.
Medications — In addition to medications that suppress the immune system, certain steroids and drugs that make the skin very sensitive to sunburns can increase the risk of developing squamous cell carcinoma. These drugs include vandetanib (Caprelsa), vemurafenib (Zelboraf), voriconazole (Vfend), and BRAF inhibitors such as dabrafenib (Tafinlar), encorafenib, and vemurafenib.
Psoriasis treatment — Psoralens and ultraviolet light (PUVA) treatments given to some psoriasis patients can increase the risk of developing squamous cell skin cancer and probably other skin cancers.
Human papilloma virus (HPV) — Research shows that this virus is a risk factor for squamous cell carcinoma, particularly if the person’s immune system becomes suppressed. Some HPV types, especially those that affect the genital and anal areas and the skin around the fingernails, seem to be related to skin cancers in these areas.
Moles — People with many moles or unusual moles (called dysplastic nevi or atypical moles) have a higher risk of developing melanoma. Dysplastic nevi are large moles that have irregular color and shape. They can appear on skin exposed to the sun as well as skin that is usually covered, such as on the buttocks or scalp. The chance of any single mole turning into cancer is very low, but anyone with many irregular or large moles is at increased melanoma risk. Moles present at birth (called congenital melanocytic nevi) are associated with a lifetime melanoma risk of 0 to 10 percent, depending on the size and number of moles.
Familial melanoma and family history — Your risk of developing melanoma is 2 to 3 times higher than average if one or more of your first-degree relatives (parents, siblings, or children) has had it. Around 10 percent of all people with melanoma have a family history of the disease. The increased risk might be because of a shared family lifestyle of frequent sun exposure, a family tendency to have fair skin, certain inherited gene changes (mutations), or a combination of factors. Only a very small number of families with a history of melanoma actually pass genetic mutations from generation to generation.
Inherited conditions — Genetic conditions associated with an increased risk of developing basal cell carcinoma include nevoid basal cell carcinoma syndrome (also called Gorlin syndrome) and Rombo, Bazex-Dupré-Christol, and epidermolysis bullosa simplex syndromes, among others. Syndromes associated with an increased risk of squamous cell carcinoma include xeroderma pigmentosum, albinism, epidermolysis bullosa simplex, dyskeratosis congenita, and multiple self-healing squamous epitheliomata. Genetic conditions associated with an increased risk of developing melanoma include xeroderma pigmentosum, retinoblastoma, Li-Fraumeni syndrome, Werner syndrome, dysplastic nevus syndrome (also called familial atypical multiple mole melanoma syndrome, or FAMMM), and certain hereditary breast and ovarian cancer syndromes.
Merkel cell polyoma virus (MCV) — Research suggests a link between this virus and Merkel cell cancer. MCV is present in up to an estimated 80 percent of Merkel cell cancers. However, scientists believe MCV is common, while Merkel cell cancer is not. More research is needed.
Symptoms of skin cancer
Basal cell carcinomas
Basal cell cancers usually develop on areas exposed to the sun, especially the face, head, and neck, but they can occur anywhere on the body. They might bleed after shaving or after a minor injury.
Firm, pale, yellow, or waxy areas, similar to a scar and with a poorly defined border
Raised reddish patches or irritated areas that may crust or itch but rarely hurt
Small, pink or red, translucent, shiny, pearly bumps, which might have blue, brown, or black areas
Pink growths with raised edges and a lower area in their center, which might contain abnormal blood vessels spreading out like the spokes of a wheel
Open sores (which may have oozing or crusted areas) that don’t heal, or that heal and then come back
Squamous cell carcinomas
Squamous cell cancers can often crust and bleed. They tend to occur on sun-exposed areas of the body such as the face, ear, neck, lip, and back of the hands. Less often, they form in the skin of the genital area. They can also develop in scars or skin sores elsewhere.
A persistent, scaly red patch with irregular borders that may crust or bleed easily
Open sores (which may have oozing or crusted areas) that don’t heal, or that heal and then come back
Raised growths or lumps, sometimes with a lower area in the center
The most important warning sign of melanoma is a new spot on the skin or a spot that is changing in size, shape, or color. Another important sign is a spot that looks different from all of the other spots on your skin. These warning signs can be remembered as the “ABCDE” rule:
Asymmetry — The shape of one-half of the mole does not match the other.
Border — The edges are ragged, notched, uneven, or blurred.
Color — Shades of black, brown, and tan may be present, as well as areas of white, gray, red, or blue.
Diameter — The diameter is usually larger than 6 millimeters (about 1/4 inch, or the size of a pencil eraser) or has grown in size. Melanoma may be smaller when first detected.
Evolving — The mole has been changing in size, shape, color, or appearance, or it is growing in an area of previously normal skin. Also, when melanoma develops in an existing mole, the texture of the mole may change and become hard or lumpy. A melanoma skin lesion is usually not painful, but it may feel different and may itch, ooze, or bleed.
Other warning signs of melanoma
A sore that doesn’t heal
Spread of pigment from the border of a mole into surrounding skin
Redness or a new swelling beyond the mole’s border
Merkel cell cancer
Some types of skin cancer spread along the nerves and can cause itching, pain, numbness, tingling, or a crawling sensation under the skin. Other signs may include lumps or bumps under the skin in areas such as the neck, armpit, or groin.
Pale, firm, shiny lumps (that can be red, pink, or blue) on the skin
How is skin cancer treated with radiation?
Electron beam radiation is usually used to treat skin cancer. This radiation uses a beam of electrons that don’t go any deeper than the skin, to help protect other organs and body tissues. Brachytherapy, which places radiation very close to or inside the skin cancer, is less commonly used.
Radiation can be used as the main treatment if a tumor is very large or is on an area of the skin that makes it hard to remove with surgery, such as on the eyelid, the tip of the nose, or the ear.
Radiation can be used in some people who cannot have surgery or who would like to avoid scarring from surgery.
Radiation can be used to cure small basal or squamous cell skin cancers and can delay the growth of more advanced cancers.
Radiation can be used to kill any remaining cancer cells that may not have been visible during surgery, and to lower the risk of cancer returning.
Radiation can be used to help treat skin cancer that has spread to lymph nodes or other organs.
Radiation is not often used to treat melanoma on the skin, although it’s sometimes used if surgery is not an option.
Radiation can be used after surgery to treat desmoplastic melanoma, an uncommon type.
Radiation is often used as palliative therapy to relieve symptoms caused by the spread of the melanoma, especially to the brain or bones.
Radiation is often given after surgery for stage I and II Merkel cell cancer.
More extensive information about skin and other cancers may be found at these sites:
American Cancer Society: Cancer.org
American Society of Clinical Oncology: Cancer.net
National Cancer Institute: Cancer.gov