What are basal and squamous cell skin cancers?
To understand basal and squamous cell skin cancers, it helps to know a little about the skin.
The skin is the largest organ in your body. It does many things:
- Covers the internal organs and helps protect them from harm
- Keeps out germs
- Prevents the loss of too much water and other fluids
- Helps control body temperature
- Protects the rest of the body from ultraviolet (UV) rays
- Helps the body make vitamin D
The skin has 3 layers. From the outside in, they are:
The top layer of the skin is the epidermis. It is very thin and protects the deeper layers of skin and the organs. The bottom of the epidermis is made up of basal cells. The basal cells divide to form keratinocytes, which make a protein called keratin. Keratin helps the skin protect the body.
The outermost part of the epidermis is made of keratinocytes that are shed as new ones form. The cells in this layer are called squamous cells.
Another type of cell, the melanocyte, is also found in the epidermis. These cells make the brown pigment called melanin. Melanin is what makes the skin tan or brown. It helps protect the deeper layers of the skin from some of the harmful effects of the sun.
A layer called the basement membrane separates the epidermis from the deeper layers of the skin. The basement membrane is important because when a cancer becomes more advanced it grows through this barrier.
The middle layer of the skin is called the dermis. The dermis is much thicker than the epidermis. It contains hair shafts, sweat glands, blood vessels, and nerves.
The deepest layer of the skin is called the subcutis. The subcutis keeps in heat and has a shock-absorbing effect that helps protect the body’s organs from injury.
Types of skin cancer
Because they behave differently, skin cancers are divided into 2 major groups.
Cancers that start from the pigment-making cells of the skin (the melanocytes) are called melanomas. Melanocytes can also form growths called moles that are not cancer. Melanoma and moles are discussed our document, Melanoma Skin Cancer.
Most skin cancers belong to a group called keratinocyte carcinomas or keratinocyte cancers because their cells look a lot like keratinocytes (the most common cell type in normal skin). Carcinoma is a medical word for a cancer that starts in a lining layer of cells (like the skin or the lining cells of the digestive system). The 2 most common types are basal cell carcinoma and squamous cell carcinoma.
Basal cell cancer
About 8 out of 10 skin cancers are basal cell carcinomas. This is not only the most common type of skin cancer, but the most common type of cancer in humans. Basal cell cancer begins in the lowest layer of the epidermis, the basal cell layer. It usually begins on skin exposed to the sun, such as the head and neck. Basal cell carcinoma was once found mostly in middle-aged or older people. But now it is also being seen in younger people. This may be because people are spending more time out in the sun.
Basal cell carcinoma tends to grow slowly. It is very rare for a basal cell cancer to spread to distant parts of the body. But if it is not treated, it can grow into nearby areas and spread into the bone or other tissues under the skin.
After treatment, basal cell carcinoma can come back (recur) in the same place on the skin. New basal cell cancers can also start in other places on the skin. As many as half of the people who have one basal cell cancer will get a new skin cancer within 5 years.
Squamous cell cancer
This type of cancer starts in the squamous cells in the upper part of the epidermis. It accounts for about 2 out of 10 skin cancers. It most often starts on skin that has been exposed to the sun, like the face, ears, neck, lips, and backs of the hands. It can also start in scars or chronic skin sores elsewhere. Less often, it forms in the skin of the genital area.
Squamous cell carcinomas are more likely than basal cell carcinomas to spread into fatty tissues just beneath the skin. They are also more likely to spread to nearby lymph nodes (the bean-shaped collections of immune system cells) or to distant parts of the body, but this is not common.
Keratoacanthomas are dome-shaped tumors that are found on sun-exposed skin. They may start out growing quickly, but their growth usually slows down. Many shrink or even go away on their own over time without any treatment. But some keep on growing, and a few may even spread to other parts of the body. Many cancer experts think of them as a type of squamous cell skin cancer and treat them as such.
Less common types of skin cancer
There are also some other types of skin cancers that are not melanomas or keratinocyte cancers. These are not very common and account for less than 1% of all skin cancers. They include:
- Merkel cell carcinoma
- Kaposi sarcoma
- Lymphoma of the skin
- Skin adnexal tumors
- Sarcomas (soft tissue cancers)
Pre-cancerous and pre-invasive skin conditions
These conditions may develop into skin cancer over time, or they may be very early stages of skin cancer.
Actinic keratosis is also known as solar keratosis. It is a pre-cancer change caused by too much time in the sun. It appears as a small, rough or scaly spot that may be pink-red or flesh-colored. They are most often seen on the face, ears, back of the hands, and arms of middle-aged or older people with fair skin.
Actinic keratoses are slow growing and do not usually cause any problems. They can go away on their own or, in some cases, they may turn into squamous cell cancers, but this does not happen very often. Still, they are a sign that your skin has been damaged by the sun. Some actinic keratoses and other skin changes that could become cancers may have to be removed. Your doctor should regularly check any actinic keratoses that are not removed to see if they have changes that could mean cancer.
Squamous cell carcinoma in situ (Bowen disease)
Squamous cell carcinoma in situ is also called Bowen disease. In situ means that the cancer is only in the epidermis where it began. This is the earliest form of squamous cell skin cancer. Bowen disease looks like scaly, reddish patches that may be crusted. The major risk factor for Bowen disease is too much sun exposure. Bowen disease in the anal and genital skin is often linked to the virus that causes genital warts (human papilloma virus or HPV).
Skin tumors that are not cancer
Most skin tumors are benign, that is, not cancer. These rarely, if ever, turn into cancers. These tumors include:
- Most types of moles (see our document, Melanoma Skin Cancer for information on moles)
- Seborrheic keratoses – tan, brown, or black raised spots with a waxy texture or rough surface
- Hemangiomas – benign blood vessel growths often called strawberry spots or port wine stains
- Lipomas – soft tumors made up of fat cells
- Warts – rough-surfaced growths caused by a virus
Last Medical Review: 09/18/2012
Last Revised: 01/17/2013