The skin is the largest
organ in the body, playing a vital role in regulation of the body's temperature
and fluid balance, as well as protecting the structures beneath it from
injury or invasion by microorganisms.
BCC, SCC, and MM develop from cells that are part of the uppermost level
of the skin, the epidermis. The epidermis has three layers: a protective
top layer; a middle layer containing squamous cells; and a bottom
layer containing basal cells. Melanocytes, usually found
just above the basal cells, produce melanin, which is responsible for
skin pigmentation. In response to UV exposure, melanocytes release additional
melanin granules in an attempt to reduce radiation damage to skin cells.
. Basal cell carcinoma (BCC)
A . Basal
cell carcinoma (BCC) BCC is the most common type of skin cancer. It originates
in the basal cells occurring at the lowest layer of the epidermis, and
is the result of chronic UV radiation exposure over time. BCC develops
slowly, usually appearing on parts of the skin that are exposed to the
sun, such as the top of the head, the tops of ears, the face, and the
neck. Although it rarely spreads to other parts of the body, it can invade
the surrounding skin, bone, or other structures, causing severe disfigurement.
Removal of BCC at this advanced stage can mean the loss of a nose, eye,
or ear. BCC often recurs in the same area, and predisposes 35% to 50%
of people to develop a second BCC within five years. Usually, BCC develops
in middle-aged or elderly adults, but is now increasingly being seen in
. Squamous cell carcinoma (SCC)
SCC is less
common than BCC. It originates in the squamous cells of the epidermis,
and is also the result of chronic UV radiation exposure over time. It
is usually found on sun-exposed parts of the head, face (including the
lip), and the hands. SCC can invade tissues beneath the skin, and may
eventually metastasize (spread) to the lymph nodes and on to other organs.
. Malignant melanoma (MM)
[ 4 ]
skin, melanocytes manufacture melanin, which is responsible for skin pigmentation.
When exposed to UV radiation, melanocytes release melanin to protect skin
cells against the destructive effects of UV radiation. The visible result
of this activity is a tan. The exact mechanism by which melanocytes become
cancerous is still under study, although there is growing evidence linking
this process to severe, intermittent, exposure to UV radiation. When experienced
before the age of 15, this type of UV radiation damage, leading to blistering
sunburn, is thought to double the risk of developing MM. [
13 ] MM most often develops on the torso of men and the lower legs
of women, but may occur on any part of the body. In darker-skinned people,
MM is commonly found under nails, between toes, on the soles of feet,
and on the palms of hands. Because MM frequently occurs in places not
exposed to UV radiation, it is imperative that skin cancer prevention
initiatives not only include visual re p resentations of melanoma lesions,
but also instructions for full skin self-exams.