Overview of Non-Melanoma Skin Cancer
The skin is the largest organ of the body. It is highly specialized, and it has many functions, including protection from the environment, heat regulation, removal of excess water and salts, production of vitamin D, and the sensation of touch. Skin cancer, like other cancers, is a disease that results from the unrestrained growth and division of cells.
The skin is made up of three distinct cell layers: (1) the epidermis, (2) the dermis, and (3) the hypodermis (see Skin Anatomy). Under normal circumstances, skin cells divide in an orderly manner to maintain tissue health. When growth control is lost, a cellular mass, or tumor, forms. Most skin tumors are benignthat is, they are not cancerous and are not likely to turn into cancer. In this category, for example, are most moles, "strawberry spots," and warts. However, if the tumor spreads to surrounding tissues or organs, it is considered malignant, or cancerous.
There are two major types of skin cancer:
- Non-melanoma (basal cell carcinoma and squamous cell carcinoma)
Each is associated with excessive sun exposure, and each can be deadly. Melanoma is far less common than basal cell carcinoma or squamous cell carcinoma of the skin, but it is much more dangerous in nature. This is because melanoma is more likely to metastasizethat is, to spread via cells that break away from the original tumor, travel through the blood or lymphatic vessels (tubes that carry fluid from the tissues) and grow within other parts of the body.
Although basal cell carcinoma, squamous cell carcinoma, and melanoma are the most common skin cancers, the skin may be the site of other cancers. These include Kaposi's sarcoma, a blotchy malignancy often associated with AIDS; mycosis fungoides, T-cell lymphoma of the skin. Paget's disease, an inflammatory cancer that usually affects the breast tissue; apocrine (glandular) carcinoma of the skin; and cancer that has metastasized from another primary site.
Nearly everyone likes a tan - it looks good and makes people feel healthy. But tanning is more dangerous and less healthful than you might think. The tan that many people strive for is the work of specialized skin cells known as melanocytes. Melanocytes produce melanin, a pigment that darkens the skin. Exposure to ultraviolet (UV) radiation from the sun "turns on" the melanocytes so that they make larger amounts of melanin and produce a tan. However, this same exposure can damage the melanocytes' DNA (deoxyribonucleic acid, the chemical that encodes the genes - the body's "building blocks"). Such damage is believed to lead to the development of skin cancer.
Because the ozone layer - the layer of atmospheric gas that filters out UV radiation - has become dangerously depleted during the 20th century, more UV rays are reaching the earth. Consequently, there are a growing number of people with skin cancer.
Skin Cancer Facts & Figures
The number of new skin cancer cases reported each year is increasing at an epidemic rate. At the present time, skin cancer is the most common cancer, accounting for nearly half of all malignancies. Sun exposure and loss of the ozone layer play a large role in cancer development among the growing population of individuals who are diagnosed with this disease. About 80% of new skin cancer cases will be basal cell carcinoma, 16% will be squamous cell carcinoma, and 4% will be malignant melanoma.
Non-Melanoma Skin Cancer Incidence
Each year in this country, approximately 1 million cases of non-melanoma skin cancers are detected. Over 500,000 people develop basal cell carcinoma, and the rest develop squamous cell carcinoma. But, like malignant melanoma, these numbers probably do not reflect the true incidence of these cancers. In 1999, it is estimated that roughly 1,900 people will die from non-melanoma skin cancer. Yet, overall, non-melanoma skin cancers account for less than 0.1% of deaths due to cancer.
Basal cell carcinoma is the most frequently diagnosed skin cancer in whites, and squamous cell carcinoma is the second most common skin cancer. In dark-complexioned individuals, squamous cell carcinoma is the most common skin cancer, whereas basal cell cancer is less often diagnosed in this population.
Basal cell carcinoma accounts for approximately 75% of the non-melanoma skin cancers diagnosed annually in the United States. The incidence of basal cell cancer increases with age. It tends not to metastasize (spread) to distant sites. The typical basal cell cancer appears on the skin as a slow-growing, pink or skin-colored lesion. More than 99% of people with basal cell carcinomas are alive five years after diagnosis. People with metastatic disease have lower survival rates.
Squamous cell carcinoma often occurs on the skin areas that are damaged by sun exposure. The most frequent areas are the neck, face, back, forearm, and the backs of the hands. Squamous cell cancers most often appear as red, hard nodules that expand rapidly. Unlike basal cell cancers, squamous cell carcinomas can metastasize. Despite this fact, the 5-year survival rate is greater than 95% in squamous cell carcinoma patients.
The skin is the largest organ of the body. It covers the internal organs, serves as a barrier against germs, regulates body temperature, prevents the loss of bodily fluids, removes excess water and salts, produces vitamin D, and interacts with the brain to generate the sensations of touch, pain, and temperature. The skin varies in depth in different parts of the body. It is noticeably thickest over the palms of the hands and the soles of the feet, where it is hard and horn-like in composition. It usually is thicker in men than in women, and it is thicker in adults than in children.
The skin is composed of three distinct cell layers - the epidermis, the dermis, and the hypodermis (subcutis) - which make up the top, middle, and bottom layers, respectively.
The epidermis forms the outermost surface of the skin. It is very thin, averaging only about 0.2 millimeters (roughly 1/100 inch) in thickness. The epidermis itself is composed of several layers, or strata, of cells.
- Stratum corneum, or horny layerouter cells of this layer are scaly. They are made up of dead keratinocytescells that contain the hard protein.
- Stratum lucidumclear, closely packed, scale-like cells that lie beneath the stratum corneum. The living keratinocytes in this and lower layers are known as squamous cells.
- Stratum granulosumflattened, spindle-shaped cells that contain granules of eleidin, a forerunner of keratin.
- Stratum Malphighiicolumnar and rounded filament-covered cells ("prickle cells") of the deep epidermis.
- Stratum germinativumdeepest, germ cell layer of the epidermis.
Fingernails and hair are appendages of the skin that are formed from the cells of the epidermis.
The deepest epidermal layers also contain the cells known as melanocytes. Melanocytes produce melanin - the pigment that gives the skin its color and helps to shield the underlying skin from the sun's harmful rays. Beneath the epidermis is the basement membrane, which separates this layer from the deeper tissues.
The epidermis is attached or "molded" to the dermis, the inner layer of the skin, by the papillary (cone-shaped) ridges that hold it in place. The dermis is thicker than the epidermis. It is tough, flexible, and elastic due to a protein known as collagen, which is made by skin cells called fibroblasts. The dermis contains connective tissue, blood vessels, lymphatic vessels, and nerves. Also embedded in the dermis are hair shafts and glands. The sweat glands manufacture sweat, which helps to regulate body temperature. The sebaceous glands produce sebuman oily substance that lubricates the skin surface and keeps it from drying out. Both the sweat and sebaceous glands usually have ducts that extend up through the epidermis. There they open to the skin's surface via small holes known as pores.
The hypodermis, otherwise known as the subcutis, is the deepest layer of the skin. It insulates the body from extremes of heat and cold, and it has a shock-absorbing property that helps to cushion the organs below and prevent injury. The hypodermis contains a meshwork of arteries that branch off to supply the hair, glands, and other tissues within the skin. Likewise, the hypodermis contains deep lymphatic vessels and nerves that become subdivided to extend into the upper skin layers.