The skin is the body's largest organ and has several important roles, including protecting us from injury, light and infection, and maintaining the body's temperature. Though skin cells are stacked in three layers--the epidermis, the dermis, and the subcutaneous--it is the epidermis that contains three types of cells that may develop into skin cancer.
The top or outermost layer is made of dead cells that contain keratin. Keratin is a hard waxy substance that helps protect the body. Keratinocytes are the cells that make keratin, and can develop into squamous cell carcinoma.
Melanocytes are deeper within the epidermis and secrete a substance called melanin. Melanin is a pigment that gives our skin color and helps protect cells from sun damage. It is produced in response to sun exposure and is the reason fair-skinned individuals will tan. Melanocytes can develop into malignant melanoma.
At the base of the epidermis are the basal cells. All other cells in the epidermis are derived from the basal cells. Basal cells can develop into the most common type of skin cancer, basal cell carcinoma.
Causes of Skin Cancer
Healthy skin cells grow and multiply in a controlled manner. The new cells produced in the inner basal layer are pushed to the outer layer, die, and are eventually sloughed off. Each skin cell contains genetic instructions, called DNA, that dictate how it grows and functions. If the DNA is damaged and the skin cell begins to malfunction, the body is sometimes unable to repair it. Cancer occurs when these damaged cells start growing out of control, and invade their neighboring cells.
What can damage the skin cell's DNA? Exposure to the sun's ultraviolet (UV) light is the number one cause of skin cancer. There are two types of UV light that reach the earth's surface: UVA and UVB. UVB light is responsible for sunburns, affects only the outer skin layer, and has the greatest role in causing skin cancer. It is filtered by glass and its intensity varies throughout the year. UVA light also causes skin damage, has more intensity than UVB, and can reach the skin's deeper layer. It can penetrate through glass, shallow water, clouds and pollution.
Other causes of skin cancer include:
•Use of tanning booths which use high doses of UVA light.
•Immunosuppression from diseases such as HIV, chemotherapy or drugs used in organ transplant patients.
•Exposure to extremely high X-ray or radiation levels.
•Contact with particular chemicals such as arsenic, industrial tars, oils and soot.
How Skin Cancer Spreads to Other Parts of the Body
When cancer spreads from its primary location to a distant part of the body it is called metastasis. Cancer cells travel through the lymphatic or vascular system. The metastatic or secondary tumor is the same type of cancer as the original. For example, if melanoma spread or metastasized from the skin to the brain, the secondary tumor would be made up of abnormal skin cells. The tumor would be located in the brain, but it would not be composed of abnormal brain cells. The secondary tumor would be referred to as metastatic melanoma.