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Medical Description

The skin is the largest organ of the body. It protects the body from infection and prevents the loss of too much water and other fluids. The skin sends messages to the brain about heat, cold, touch and pain sensations.

The skin has three layers: the epidermis, dermis and subcutis (fat).

The top layer of the skin is the epidermis. The epidermis is a thin layer of skin that protects the deeper layers of skin and the organs. The epidermis is composed of four layers. The lower layer is made up of basal cells. A layer called the basement membrane, just under the basal layer, separates the epidermis from the other layers of skin.

The dermis, the middle layer, is much thicker than the epidermis. It contains hair shafts, sweat glands, blood vessels and nerves.

The last and deepest layer of the skin is called the subcutis. The subcutis keeps in heat and has a shock-absorbing effect, which helps protect the body's organs from injury.

Nonmelanoma skin cancers are by far the most common type of cancer worldwide. There are several types of nonmelanoma skin cancers. The two most common are basal cell carcinoma and squamous cell carcinoma. Both can usually be successfully treated.

Basal cell carcinomaBasal cell carcinoma begins in the lowest layer of the epidermis, the basal cell layer. Basal cell carcinoma accounts for about 75 percent of all skin cancers. It usually begins on the areas of the body most exposed to the sun, such as the face, neck, forearms and back of the hands.

Basal cell carcinomas

  • are usually flesh-coloured, red or black
  • appear as small, round or flattened bumps with pearly borders
  • tend to bleed following minor injury

Basal cell carcinoma was once found mostly in middle-aged and older people, but it is now developing in younger people as well, including people in their teens and 20s.

Basal cell carcinoma is a slow growing cancer and it is unusual for it to spread to distant parts of the body. However, if left untreated, it can spread to nearby areas and invade the bone or other tissues beneath the skin.

After treatment, basal cell carcinoma can recur in the same place, or a new spot may develop elsewhere on the skin. People who have had this form of skin cancer once have an increased risk of developing a new skin cancer within the next five years.

 

Squamous Cell CarcinomaSquamous cell carcinoma begins in the upper layer of the epidermis and accounts for about 20 percent of all skin cancers. It also typically appears on the areas of the body most exposed to the sun, such as the face, ears, neck, lips and backs of the hands.

This cancer may appear as a growing lump, often with a rough surface. It can appear as a thickened, red, scaly bump or wart-like growth. It may even appear as a raised crusted sore.

Squamous cell carcinomas are more likely to invade tissues beneath the skin, and are slightly more likely to spread to distant parts of the body than are basal cell carcinomas. Even so, few squamous cell skin carcinomas spread to the lymph nodes or other organs.

Bowen's disease is squamous cell carcinoma in situ. “In situ” means it is still only in the top part of the skin (the epidermis) and has not spread beyond the area in which it started. Bowen's disease is the earliest form of squamous cell skin cancer. Bowen's disease appears as reddish, scaly patches.

Bowen's disease of the anal and genital skin is often related to the human papillomavirus (HPV), a sexually transmitted infection that can also cause genital warts.

 

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Nonmelanoma Skin Cancer

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  • A publication of:
  • Women's College Hospital