Skin cancer is a disease in which malignant (cancerous) cells form in the tissues of the skin.
Most skin cancers develop on the visible outer layer of the skin (the epidermis), particularly in sun-exposed areas (face, head, hands, arms, and legs). They are usually easy to detect by examining the skin, which increases the chances of early treatment and survival.
Types of Skin Cancer
There are different types of skin cancer, each named for the type of skin cell from which they originate. The majority of skin cancers fall into one of the following categories:
- Basal cell carcinoma (also called BCC) comes from the basal cells in lowest part of the epidermis. 80-85% of skin cancers are basal cell carcinomas.
- Squamous cell carcinoma (also called SCC) comes from the skin cells (keratinocytes) that make up the top layers of the skin. About 10% of skin cancers are SCC.
- Melanoma comes from skin cells called melanocytes, which create pigment called melanin that gives skin its color. 5% of all skin cancers are melanoma. Although less common, melanomas are a very dangerous type of skin cancer and are the leading cause of death from skin disease.
Basal cell and squamous cell carcinoma are sometimes referred to as “non-melanoma skin cancer” to distinguish them from melanoma.
There are a variety of less common types of skin cancers, including cutaneous T-cell lymphoma (CTCL) and Merkel cell carcinoma.
Skin cancer is considered low risk when the affected cells remain clustered in a single group. It is considered high risk when the cells have invaded surrounding tissues. High risk forms of cancer require more aggressive treatments.
Almost all skin cancers start as a small, low-risk lesions, but can grow and become high-risk lesions if left untreated. Melanoma is the most alarming type because it has a higher risk of invading surrounding tissues or spreading to other parts of the body (metastasis) before being detected. Squamous cell and basal cell skin cancer are more likely to be detected and treated effectively before they become malignant.
If skin cancer is detected before it has spread to surrounding tissues, chances of a complete cure are excellent.
Precancerous skin lesions (precancers)
Skin cancer may often be preceded by lesions called pre-cancers. The most well-known of these lesions is called actinic keratoses (AKs).
An actinic keratosis lesion is considered an early form of squamous cell carcinoma. An actinic keratosis, a new or changing mole (nevi), and other unusual lesions on your skin should be carefully monitored and brought to the attention of your doctor.
Cause of Skin Cancer
Sunlight is composed of visible light (all the colors we see in daylight), infrared radiation (which provides warmth), and ultraviolet (UV) radiation, which is carcinogenic (cancer-causing). More than 90% of all skin cancer is caused by long-term exposure to UV radiation.
UV radiation damages the skin’s DNA, causing a cell to behave abnormally. The body normally has mechanisms to repair damaged DNA but these repair mechanisms do not function normally after exposure to UV radiation. This allows the abnormal skin cell to replicate itself, making more cells with the same damaged DNA. This growing collection of abnormal cells is the beginning of a cancer.
The immune system can often detect and destroy cancer cells, just as it defends against infections by bacteria or viruses. However, UV radiation disrupts the immune system so that our natural defenses may not detect the cancer, allowing it to grow unchecked.
Melanin in the skin, which gives skin its tan to brown color, can block the damaging effects of UV radiation. The more melanin, the darker the skin. And the darker the skin, the better protected it is from UV radiation. This is why a body darkens when exposed to sunlight (tanning). It is trying to build a better barrier to UV light.
However, the melanin provides only partial protection, even for those with very dark skin. And those with fair skin have almost no melanin to protect them.
It is important to remember that a tan develops only AFTER the skin has been damaged by UV radiation, and that this tan provides only minor protection from additional damage.
In addition to sun exposure, family history may also play a role in a small percentage of skin cancers, especially melanomas.
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