What is skin cancer?

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.

Bibliography

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