What is skin cancer?

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Malignancies of the skin (and sometimes spreading to the internal organs) caused by the ultraviolet radiation in sunlight.
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Cancer is the common term used to describe the large class of diseases called neoplasms. Neoplasms, which occur only in multicellular organisms, develop and function in an autonomous way that does not abide by the biological mechanisms that govern the growth and apoptosis of healthy cells. When such neoplasms grow at a rate faster than the tissues from which they arise, while at the same time invading those tissues, they are called malignant and are commonly described as cancerous. Benign neoplasms, which do not invade surrounding tissues, generally are not as dangerous as malignant ones.

Sun radiation is life-sustaining, but the higher-energy spectrum of sunlight brings the danger of skin damage and skin cancer. When living tissue is irradiated, its molecular structure is disrupted, thus initiating a chain of reactions, many of which are not the usual ones associated with the living organism. Therefore, a change in the chromosomal composition and the development of unwanted cells is likely to occur. Such changes take place because of the formation of free radicals in the deoxyribonucleic acid (DNA) molecules that constitute the genetic code. The result is skin cancer, one of the most common forms of cancer in both men and women.

Types of skin cancer. Skin neoplasms may be benign or malignant, acquired or congenital, although the majority are benign and acquired. The common mole (the medical term for which is melanocytic nevus) is a neoplasm of benign melanocytes that is often present at birth and that is known as a birthmark. Such moles are generally harmless unless they are large in size, in which case they may have up to a 10 percent chance of becoming malignant. Other melanocytic nevi are strawberry hemangiomas and port-wine stains, which are of vascular origin.

The most common form of skin cancer are keratinocyte cancers such as basal cell carcinomas and squamous cell carcinomas, which arise from the main cell type of the epidermis (keratinocytes) and are most often caused by the cumulative effects of ultraviolet radiation on the skin. They are generally localized, however, and rarely metastasize. These cancers are easily identified as persisting sores or crusting patches that grow mostly on sun-exposed parts of the body such as the hands, neck, arms, and face. They can be treated with routine surgical procedures.

A malignant melanoma is formed from the pigment-forming melanocyte and almost certainly undergoes metastasis. It should therefore be removed surgically at the earliest possible stage. If the melanoma is detected at a later stage, chemotherapy and irradiation are the techniques usually applied. A malignant melanoma appears as a lesion that increases in size and turns several colors, such as black, blue, white, and brown. Symptoms such as itching, bleeding, and pain are not as common at first but may be encountered at later stages of development.

There are two additional skin malignancies that may be fatal: mycosis fungoides and Kaposi’s sarcoma. Mycosis fungoides is a skin lymphoma that may be confined to one location for ten or more years before it metastasizes to internal organs, when it can become life threatening. As a result, it is difficult to track this skin cancer, both clinically and histologically, and several biopsies (skin histological examinations) may be required to ascertain its presence. On the other hand, Kaposi’s sarcoma occurs either as lesions (commonly among older Mediterranean men) or as skin abnormalities in people with human immunodeficiency virus (HIV) infection. The sarcoma is derived from skin blood vessels and appears as violet patches or lesions. As long as it is contained only in the skin, it is not fatal. Once the inner organs are affected, however, it can become life threatening, even though the lesions may be treated with irradiation and chemotherapy.

The effects of sunlight on skin. Chronic skin exposure to sunlight leads to the polymerization of skin chemicals (known as catecholamines) and the subsequent formation of different types of epidermal pigmentation (the melanins), which are responsible for tanning. Tanning occurs only if there is gradual exposure to sunlight; otherwise, a sunburn will arise. Photoprotection is believed to be one of the major biological functions of the melanin pigment. It appears that melanin formation can participate effectively in reducing the harmful effects of sunlight by an array of photoinduced chemical reactions, which result in the consumption of scavenging active oxygen species such as the superoxide anion and hydrogen peroxide. It has been determined that in biological systems, superoxide and hydrogen peroxide are formed in small quantities during normal processes. Both species are known to produce several biological effects, most of which are harmful to tissues. It should be pointed out, however, that although melanin may act as a free radical scavenger, it may also become energetically overloaded and may change to a toxic state. Evidence exists that melanin increases the radiative damage to cells, which leads to sunlight-induced skin cancer. In other words, melanin formation is good only when moderate exposure to sunlight occurs.

In the atmosphere twelve to forty-eight kilometers above the earth’s surface lies a small layer of ozone. Although this layer does not contain much ozone—it is estimated to be about three millimeters thick under normal conditions of temperature and pressure—it has a profound effect on life. The ozone layer absorbs the harmful ultraviolet radiation from the sun, thus providing the mechanism for the heating of the stratosphere. A reduction in the ozone layer would lead to a large increase of ultraviolet rays intruding into the atmosphere, thus increasing the incidence of skin cancer. F. S. Rowland and M. J. Molina declared in 1974 that the presence of the volatile chlorofluorocarbons would eventually reduce the ozone layer. Some measurements done by scientists in 1979 showed a decrease in the layer, which led to the action taken by several governments to decrease and replace the chlorofluorocarbons commonly used in aerosols. The coordinated international action has slowed the depletion of the ozone layer, although significant thinning occurred over the Antarctic. The highest incidence of melanoma worldwide is reported in Australia. As the average life span of humans steadily increases, the incidence of skin cancer will likely increase as well; however, education about skin cancer prevention will hopefully reduce the number of cases and improved diagnosis and treatments have increased survival rates. Sunscreens with sun protecting factor (SPF) of at least 30 and hats and sunglasses with high ultraviolet blocking are recommended for people who are exposed to large amounts of sunlight, particularly those with fair skin who are at a higher risk of developing skin cancer due to sun damage.


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