Overview of Skin Cancer
Medically reviewed by Dr. C.H. Weaver M.D. Medical Editor 10/2018
More than one million new cases of skin cancer are diagnosed each year in the United States, making it the most commonly diagnosed type of cancer.(1)
Overview of the Skin
The skin is the largest organ in the body. It protects against germs, covers internal organs, and helps regulate the body’s temperature. The two main layers of the skin are the epidermis and the dermis. The epidermis forms the top, outer layer of the skin. The dermis is a thicker layer beneath the epidermis.
Skin cancer generally develops in the epidermis. The three main types of cells in the epidermis are squamous cells, basal cells, and melanocytes. Squamous cells form a flat layer of cells at the top of the epidermis. Basal cells are round cells found beneath the squamous cells. Melanocytes are pigment-producing cells that are generally found in the lower part of the epidermis.
Types of Skin Cancer
Skin cancer is often categorized as melanoma or non-melanoma. Melanoma is a cancer that begins in melanocytes. It is less common than non-melanoma skin cancer, but tends to be more aggressive. In 2006 an estimated 62,000 individuals in the U.S. will be diagnosed with melanoma, and close to 8,000 will die of the disease.(1)
The most common type of non-melanoma skin cancer is basal cell carcinoma. This type of cancer rarely spreads to distant sites in the body, but it can be disfiguring and may invade nearby tissues.
The second most common type of non-melanoma skin cancer is squamous cell carcinoma. Although this type of cancer is more likely to metastasize (spread to lymph nodes or other sites in the body) than basal cell carcinoma, metastasis is still rare. Both basal cell carcinoma and squamous cell carcinoma most commonly develop on sun-exposed parts of the skin, but can develop on other parts of the skin as well.
An alarming trend in both melanoma and non-melanoma skin cancers is that the frequency of these cancers in children and young adults appears to be increasing.(2) This highlights the importance of prevention at all ages.
Because of their very different characteristics and treatment, melanoma and non-melanoma skin cancer are discussed further in separate sections.
Screening and Prevention of Skin Cancer
Physicians and individuals alike recognize that the best “treatment” of cancer is preventing its occurrence in the first place or detecting it early when it may be most treatable.
The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait such as eye color. Non-genetic factors include behaviors such as diet and exercise, as well as exposure to substances in the environment. Many non-genetic factors are modifiable, allowing us to take steps to reduce our risk of cancer.
Hereditary or Genetic Factors
The frequency of skin cancer varies by skin, eye, and hair color. Fair-skinned individuals; those with blue, green, or grey eyes; and those with red or blonde hair are at increased risk.(1,2) Skin cancer can also develop in individuals with darker skin or eye color, which suggests that that prevention is important for everyone.
Individuals with a family history of skin cancer are also more likely to develop skin cancer. In rare cases, this is due to a known familial cancer syndrome such as xeroderma pigmentosum, oculocutaneous albinism, or basal cell nevus syndrome. Individuals with xeroderma pigmentosum are extremely sensitive to ultraviolet radiation and have a very high probability of developing skin cancer. Oculocutaneous albinism involves a defect in melanin production, and results in complete or partial absence of pigment in the skin, hair, and eyes. Basal cell nevus syndrome causes disorders of the skin as well as other parts of the body, including the bones and nervous system.
Environmental or Non-Genetic Factors
Exposure to ultraviolet radiation is the most important risk factor for both basal cell carcinoma and squamous cell carcinoma.(1,2) The ultraviolet radiation from the sun that reaches the earth includes both ultraviolet B (UVB) and ultraviolet A (UVA). Both types of ultraviolet radiation are thought to increase skin cancer risk. Exposure to ultraviolet radiation from the sun is greatest at latitudes closer to the equator, at high altitude, and when the sun in highest in the sky.
Tanning beds and sun lamps also provide exposure to ultraviolet radiation, and are believed to increase the risk of skin cancer.(3)
Actinic keratoses are a type of precancerous change to the skin that is caused by sun exposure. They are signs of damage to the skin and in some cases progress to squamous cell carcinoma.
Infection with certain types of human papillomavirus may also increase the risk of non-melanoma skin cancer. These viruses are very common, and are responsible for conditions ranging from warts to cervical cancer. Though relatively few studies have evaluated a link with skin cancer, there is some suggestion that a certain class of HPV known as beta HPV plays a role in squamous cell carcinoma.(4) This class of HPV includes HPV types 5,8,9,15,20,24,36, and 38.
Patients who are immunosuppressed, such as those undergoing organ transplantation, have a greatly increased risk of developing non-melanoma skin cancer.(1,2) Immunsuppression may also influence the type of skin cancer that develops–in contrast to the general population, organ transplant recipients are more likely to develop squamous cell carcinoma than basal cell carcinoma.(2)
Other factors linked with non-melanoma skin cancer include ionizing radiation (such as radiation from x-rays), arsenic, oral methoxsalen, and ultraviolet A therapy for psoriasis, ulcers or inflammation of the skin, and smoking.(1-4)
Prevention of Skin Cancer
Though common, non-melanoma skin cancer is a largely preventable disease. Sun protection over the course of a lifetime is the most important aspect of prevention. You can protect yourself from the sun by using a high-SPF sunscreen that protects against UVB and UVA, wearing sun-protective clothing (such as hats, long-sleeved shirts, and long pants) with a tight weave, wearing sunglasses, and by staying in the shade. When using sunscreen, apply a large amount and reapply frequently. It’s also important not to use sunscreen as an excuse for longer sun exposure. Individuals who use sunscreen to extend their time in the sun expose themselves to the same amount of UV radiation as if they had remained outside for a shorter period of time without sunscreen.
Keep in mind that that UV radiation can be reflected off of snow, water, and sand. UV radiation is also more intense at high altitudes, at latitudes closer to the equator, and when the sun is higher in the sky. Because sun lamps and tanning booths also expose you to ultraviolet radiation, use of these tanning devices is best avoided.(5)
For individuals with actinic keratoses, a precursor to squamous cell carcinoma, removal of the lesions may decrease the risk of developing squamous cell carcinoma. Because actinic keratoses are a sign that the skin has been damaged by sun exposure, individuals with actinic keratoses will also need to take special care to protect their skin from further sun damage.
Screening and Early Detection
Though the U.S. Preventive Services Task Force has concluded that there is insufficient evidence to recommend routine skin cancer screening or skin self-exam,(7,8,9) individuals and their physicians should be aware of changes to the skin that may signal cancer.
The most common signs of non-melanoma skin cancer involve changes to the skin, such as a new growth, changes in an old growth, or a sore that doesn’t heal.
Self Exam: Performing skin self-examinations on a monthly basis may help you monitor changes to your skin. Use a mirror to examine your entire body for skin changes. It may be helpful to have someone with you to help examine hard-to-see areas such as your back. If you notice suspicious changes to your skin, you should promptly notify your physician.
Routine check-up: Depending on your age and personal and family history, a skin examination may be conducted as part of your regular health exams.
Careful follow-up: Within the first five years of a diagnosis of non-melanoma skin cancer, an estimated 30% to 50% of patients will develop another non-melanoma skin cancer.(6) Patients who have had non-melanoma skin cancer are also at increased risk of developing melanoma.(9) Because of this high risk, individuals with a history of skin cancer should follow their physician’s recommendation regarding ongoing follow-up exams.
- American Cancer Society. Cancer Facts and Figures 2006. Available at http://www.cancer.org/docroot/STT/stt_0.asp (Accessed April 17, 2006)
- Christenson LJ, Borrowman TA, Vachon CM et al. Incidence of Basal Cell and Squamous Cell Carcinomas in a Population Younger Than 40 Years. JAMA. 2005;294:681-690.
- Rubin AI, Chen EH, Ratner D. Basal-Cell Carcinoma. New England Journal of Medicine. 2005;353:2262-2269.
- Alam M, Ratner D. Cutaneous Squamous-Cell Carcinoma. New England Journal of Medicine. 2001;344:975-983.
- World Health Organization. Sunbeds, Tanning, and UV Exposure. Fact Sheet No. 287. March 2005. Available at http://www.who.int/mediacentre/factsheets/fs287/en/print.html (Accessed April 17, 2006)
- Karagas MR, Nelson HH, Sehr P et al. Human Papillomavirus Infection and Incidence of Squamous Cell and Basal Cell Carcinomas of the Skin. Journal of the National Cancer Institute. 2006;98:389-95.
- U.S. Preventive Services Task Force. Screening for Skin Cancer: Recommendations and Rationale. American Journal of Preventive Medicine. 2001;20(3S):44-6.
- National Comprehensive Cancer Network. Basal Cell and Squamous Cell Skin Cancers. Clinical Practice Guidelines in Oncology – v.2.2005. © National Comprehensive Cancer Network, Inc. 2001, 2002, 2003, 2004, 2005. NCCN and NATIONAL COMPREHENSIVE CANCER NETWORK are registered trademarks of National Comprehensive Cancer Network, Inc.
- Rosenberg CA, Khandekar J, Greenland P et al. Cutaneous Melanoma in Postmenopausal Women After Nonmelanoma Skin Carcinoma: The Women’s Health Initiative Observational Study. Cancer. 2006;106:654-63