Skin Cancer Health Article

Definition

Skin cancer is a malignant growth of the external surface or epithelial layer of the skin.

Description

Skin cancer is the growth of abnormal cells capable of invading and destroying other associated skin cells. Skin cancer is often subdivided into either melanoma or non-melanoma. Melanoma is a dark-pigmented, usually malignant, tumor arising from a skin cell capable of making the pigment melanin (a melanocyte). Melanoma can spread throughout the body via the bloodstream or lymphatic system. Non-melanoma skin cancer most often originates from the external skin surface as a squamous cell carcinoma or a basal cell carcinoma.

The cells of a cancerous growth originate from a single cell that reproduces uncontrollably, resulting in the formation of a tumor. Exposure to sunlight is documented as the main cause of almost 800,000 cases of skin cancer diagnosed each year in the United States. The incidence increases for those living where direct sunshine is plentiful, such as in regions near the equator.

Basal cell carcinoma affects the skin's basal layer and has the potential to grow progressively larger in size, although it rarely spreads to distant areas (metastasizes). Basal cell carcinoma accounts for 80% of skin cancers (excluding melanoma), whereas squamous cell cancer makes up about 20%. Squamous cell carcinoma is a malignant growth of the external surface of the skin. Squamous cell cancers metastasize at a rate of 2–6%, with up to 10% of lesions affecting the ear and lip.

Causes & symptoms

Cumulative sun exposure is considered a significant risk factor for non-melanoma skin cancer. High incidence has been noted in individuals with freckles, light hair, and light complexion; in individuals with darker skin, the palms, soles, mucous membranes, and other areas of light pigmentation are the most common sites for melanomas.

Pre-existing moles can change into melanomas, and should be observed for any particular change in appearance, specifically the classic ABCD appearance, in which asymmetrical borders, colors, and diameter are observed. Lesions typically are circular with irregular or asymmetrical borders. Melanomas typically have a combination of colors, including tan, brown, black, or gray; there may also be a dull pink or rose pigmentation within a small area of the lesion. The diameter of a malignant melanoma is typically greater than that of a pencil eraser.

There is evidence suggesting that early intense sun exposure causing blistering sunburn in childhood may also play an important role in the cause of non-melanoma skin cancer. Basal cell carcinoma most frequently affects the skin of the face, with the next most

common sites being the ears, the backs of the hands, the shoulders, and the arms. It is prevalent in both sexes, and most commonly occurs in people over the age of 40.

Basal cell carcinoma usually appears as a small skin lesion that persists for at least three weeks. This form of non-melanoma cancer looks flat and waxy, with the edges of the lesion translucent and rounded. The edges also contain small fresh blood vessels. An ulcer found in the center gives the lesion a dimpled appearance. Basal cell carcinoma lesions vary from 4–6 mm in size, but can slowly grow larger if left untreated.

Squamous cell carcinoma also involves skin exposed to the sun, such as the face, ears, hands, or arms. This form of non-melanoma cancer also is most common among people over the age of 40. Squamous cell carcinoma presents itself as a small, scaling, raised bump on the skin with a crusting ulcer in the center, but without itching.

Basal cell and squamous cell carcinomas can grow more easily when people have a suppressed immune system because they are taking immunosuppressive drugs or are exposed to radiation. Some people must take immunosuppressive drugs to prevent the rejection of a transplanted organ or because they have a disease in which the immune system attacks the body's own tissues, referred to as autoimmune illnesses; others may need radiation therapy to treat another form of cancer. Because of the increased risk of skin cancer, all people taking these immunosuppressive drugs or receiving radiation treatments should undergo complete skin examination at regular intervals. If proper treatment is delayed and the tumor continues to grow, the tumor cells can spread, or metastasize, to other muscles, bones, nerves, and possibly to the brain.

About 1–2% of all skin cancers develop within burn scars; squamous cell carcinomas account for about 95% of these cancers, with 3% being basal cell carcinomas and the remainder malignant melanomas.