It's easy to take skin for granted. It seems to be a simple sheath, a tender yet durable covering for our bones, muscles, and organs. In fact, the skin is itself a complex organ, the body's largest. It has a variety of important jobs, including controlling body temperature.
Perhaps because it is so large and exposed to the environment, the skin is by far the most common site of cancer. Damage from ultraviolet (UV) rays causes most cases of skin cancer.
Understanding the skin and skin cancer
The skin is made up of cells that grow and divide to make new cells. This occurs in a regulated way, with new cells replacing old cells as they die off.
When skin cells are damaged, this orderly process can turn into chaos. Abnormal cells begin to grow and divide out of control. These cells can form masses (tumors) and invade nearby tissues. How aggressive this process is depends on the kind of cell affected.
The skin has two main layers: the epidermis or outer layer and the dermis or inner layer. These layers contain different types of cells. In skin cancer, the most important ones are:
- Squamous cells, which are flat cells found just below the outer layer of the epidermis
- Basal cells, which are round cells found in the lower (or base) part of the epidermis
- Melanocytes, also in the lower epidermis, which produce the substance that can make skin tan or brown
Types of skin cancer
Skin cancers are divided into two broad categories:
- Melanoma. Melanoma is much less common than nonmelanoma skin cancers, but it is much more likely to spread and much more dangerous.
- Nonmelanoma skin cancer. The two major forms are basal cell and squamous cell carcinomas. Carcinoma is a medical term for cancer. Nonmelanoma skin cancers are grouped together because they are so different from melanoma. They have a high cure rate and are rarely life-threatening.
Melanoma starts in the melanocytes. These are pigment-producing cells. Melanomas are usually brown or black, but they can also have no color. Melanomas can occur anywhere on the skin but are most common on the chest, back, and legs.
Melanocytes can also produce moles, which are benign, or noncancerous, tumors. Most moles are harmless, but some types can turn into cancer, so you should have any mole checked by a doctor.
Melanoma causes fewer than 5 out of 100 cases of skin cancer, but it accounts for most skin cancer deaths. The rate of melanoma has been on the rise for at least the past 30 years. The largest increases have been in young white women and older white men.
Melanoma can often be cured if it is found early. If it is not found and treated, it can spread to other organs, including the lungs, liver, and brain.
Basal cell carcinoma is the most common form of skin cancer, accounting for almost 8 out of 10 cases. It grows very slowly and rarely spreads to lymph nodes or distant organs. But if it is not treated, it can grow into nearby tissues and bone.
Basal cell carcinoma usually occurs on sun-exposed areas of skin such as the nose, cheeks, and neck. It used to be common only in older people, but now it is also being diagnosed in younger people. This is probably because of their increased sun exposure.
Basal cell carcinoma is usually easy to treat, but it can come back in the same spot. Also, up to half of people who have this cancer will have another skin cancer within 5 years.
Squamous cell carcinoma accounts for up to 20 out of 100 cases of skin cancer. Like basal cell carcinomas, squamous cell cancers typically appear on skin that gets a lot of sun exposure such as the face, ears, neck, lips, or back of the hands. They can also grow within scars or skin ulcers.
Squamous cell carcinomas are more likely than basal cell carcinomas to spread to tissues beneath the skin. They can spread to lymph nodes and other organs, but this is not common.
Less common forms of nonmelanoma skin cancer include Kaposi's sarcoma, Merkel cell carcinoma, and skin lymphoma. Altogether, they account for less than 1 percent of nonmelanoma skin cancers diagnosed in the United States.
Created on 11/05/1999
Updated on 02/17/2011
- American Cancer Society. Melanoma skin cancer.
- American Cancer Society. Skin cancer: basal and squamous cell.
- National Cancer Institute. What you need to know about melanoma and other skin cancers.
- American Society of Clinical Oncology. Skin cancer (non-melanoma).