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Doctors diagnose skin cancer in more than 3 million people in the United States, according to the American Cancer Society, making skin cancer the most common type of cancer in the nation. There are several types of skin cancer, and each can look and behave differently. Almost all types of skin cancer are treatable if detected and treated early enough, so it is important to know about the different types of skin cancer.

Cancer is an abnormal growth of body cells. It is a progressive condition, which means it worsens over time. Cancer often starts in one part of the body then spreads to other organs and tissue. Skin cancer starts with abnormal skin cells in one part of the body, for example, and these abnormal cells can develop into a tumor. As skin cancer progresses, these abnormal skin cells and tumors begin appearing in nearby tissue then into lymph nodes, and then into organs far away from the original patch of abnormal skin cells. The spread of these abnormal cells and tumors can prevent healthy cells, tissues, and organs from functioning properly.

Without treatment, skin cancer can cause death. Fortunately, skin doctors can detect and treat skin cancer, so skin cancer is responsible for fewer than 1 percent of all cancer deaths.

About the Body’s Largest Organ: The Skin

In addition to protecting the body from infection and injury, the skin helps regulate body temperature. Skin also produces Vitamin D, and stores fat and water. Cancer can prevent the skin from performing these important functions. It can also spread to other tissues throughout the body.

Skin cancer affects different layers of skin:

Epidermis – the outer layer of skin

Dermis – the inner layer of skin

Hypodermis – the deep layer of fat beneath the skin

Different types of skin cells make up the various layers of skin. Cancer can start in these skin cells and in the hair follicles in the skin.

The 4 Types of Skin Cancer

1. Basal cell carcinoma

Basal cells are round skin cells located in the lower part of the epidermis. Approximately 80 percent of all skin cancers originate in basal cells; skin doctors refer to these cancers as basal cell carcinoma. This type of skin cancer develops most often on a patient’s head and neck, but the abnormal cells can develop anywhere on a person’s skin. Basal cell carcinoma is usually the result of exposure to the sun, although it can develop in people who underwent radiation therapy when they were children.

Basal cell carcinomas usually grow very slowly, and the cancer cells rarely spread to other tissues of the body. Left untreated, though, basal cell carcinoma can grow into nearby tissue and even invade the tissues beneath the skin or the bone. If not removed completely, the cancer cells can come back in the same place. Patients who have had basal cell carcinomas are also more likely to develop new skin cell cancers in other places.

2. Squamous cell carcinoma

A large percentage of the epidermis consists of flat, scale-like cells, known as squamous cells. About 20 percent of skin cancers develop from squamous cells; doctors refer to these cancers as squamous cell carcinomas. Anywhere between 2 and 5 percent of squamous cell cancers spread to other areas of the body, so it is more likely to spread than basal cell carcinoma.

Sun exposure is the main cause of squamous cell carcinoma, so this type of skin cancer can develop anywhere exposed to sunshine. Squamous cell carcinoma can also develop on burned skin, skin damaged by chemicals, and skin exposed to x-rays. Lips are a common location for squamous cell carcinoma; this type of cancer can also develop near long-standing scars and on skin outside the mouth, anus, or near a woman’s vagina.

Skin doctors can usually remove squamous cell carcinomas completely or treat the cancer in other ways. Squamous cell cancers are more likely than basal cell carcinomas to grow into deeper layers of skin or spread to other parts of the body.

3. Melanoma

Melanoma starts in melanocytes, which are cells situated in the part of skin where the epidermis meets the dermis. Melanocytes produce melanin, which is the pigment that gives skin its color.

While it is less common than basal cell carcinoma and squamous cell carcinoma, melanoma is the most serious form of skin cancer. This is because melanoma is more likely to grow and spread. Doctors diagnose about 106,110 new cases of melanomas each year; the disease will claim 7,180 lives each year.

4. Merkel cell cancer

Merkel cell cancer is a fast-growing, highly aggressive cancer. This rare form of skin cancer starts in special hormone-producing cells situated just under the skin and in hair follicles. Doctors most commonly discover it in the head and neck region.

For more information about the four main types of skin cancer, consult with a skincare specialist at the Center for Dermatology and Laser Surgery. The more you know about skin cancer, the earlier you may be able to detect and find treatment for it.