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Basal and Squamous Cell Skin Cancer
What You Need to Know â" Now
By American Cancer Society
American Cancer Society / Health PromotionsCopyright © 2012 American Cancer Society
All rights reserved.
Your Skin Cancer
What Is Cancer?
The body is made up of hundreds of millions of living cells. Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of out-of-control growth of abnormal cells.
Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. Cancer cells can also invade other tissues, something that normal cells cannot do. Growing out of control and invading other tissues are what makes a cell a cancer cell.
Cells become cancer cells because of damage to DNA. DNA is in every cell and directs all its actions. In a normal cell, when DNA is damaged, the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired, but the cell does not die like it should. Instead, this cell goes on making new cells that the body does not need. These new cells will all have the same damaged DNA as the first cell.
People can inherit damaged DNA, but most DNA damage is caused by mistakes that happen while the normal cell is reproducing or by something in the environment. Sometimes the cause of the DNA damage is something obvious, such as cigarette smoking. Often, however, no clear cause is found.
In most cases, the cancer cells form a tumor. Some cancers, such as leukemia, rarely form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.
Cancer cells often travel to other parts of the body, where they begin to grow and form new tumors that replace normal tissue. This process is called metastasis. It happens when the cancer cells get into the bloodstream or lymph vessels of the body.
No matter where a cancer may spread, it is always named for the place where it started. For example, breast cancer that has spread to the liver is still called breast cancer, not liver cancer. Likewise, prostate cancer that has spread to the bone is metastatic prostate cancer, not bone cancer.
Different types of cancer can behave very differently. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. That is why people with cancer need treatment that is aimed at their particular kind of cancer.
Not all tumors are cancerous. Tumors that are not cancer are called benign. Benign tumors can cause problems — they can grow very large and press on healthy organs and tissues. But they cannot grow into other tissues. Because they cannot invade other tissues, they also cannot metastasize, or spread, to other parts of the body. These tumors are almost never life threatening.
What Are Basal and Squamous Cell Skin Cancers?
To understand basal and squamous cell skin cancers, it helps to know about the normal structure and function of the skin.
The skin is the largest organ in your body. It does several different things:
covers the internal organs and protects them from injury
serves as a barrier to germs such as bacteria
prevents the loss of too much water and other fluids
helps control body temperature
The skin has the following 3 layers:
The top layer of skin is the epidermis. The epidermis is thin, averaging only 0.2 millimeters (mm) thick (about 1/100 of an inch). It protects the deeper layers of skin and the organs of the body from the environment.
Keratinocytes are the main cell type of the epidermis. These cells make an important protein called keratin, which gives the skin strength and flexibility and makes the skin waterproof.
The epidermis itself is made up of 3 sublayers. The outermost part of the epidermis is called the stratum corneum, or horny layer. It is composed of dead keratinocytes that are continually shed as new cells form. The cells in this layer are called squamous cells because of their flat shape.
Just below the stratum corneum are living keratinocytes. Below that is the basal layer, the inner layer of the epidermis. The cells of the basal layer, called basal cells, continually divide to form new keratinocytes. These new keratinocytes replace the older keratinocytes that slough off the skin's surface.
Cells called melanocytes are also present in the epidermis. These skin cells make the brown pigment called melanin. Melanin is what makes the skin tan or brown. It protects the deeper layers of the skin from some of the harmful effects of the sun.
The epidermis is separated from the deeper layers of skin by the basement membrane. The basement membrane is an important structure. When a skin cancer becomes more advanced, it generally grows through the basement membrane.
The middle layer of the skin is called the dermis. The dermis is much thicker than the epidermis. It contains hair follicles, sweat glands, blood vessels, and nerves that are held in place by a protein called collagen. Collagen is made by cells called fibroblasts and gives the skin its resilience and strength.
The deepest layer of the skin is called the subcutis. The subcutis and the lowest part of the dermis form a network of collagen and fat cells. The subcutis helps the body conserve heat and has a shock-absorbing effect that helps protect the body's organs from injury.
Types of Skin Cancer
Cancers that develop from melanocytes, the pigment-making cells of the skin, are called melanomas. Melanocytes can also form benign growths called moles. Melanoma and moles are discussed in the book QuickFACTS Melanoma Skin Cancer. Skin cancers that are not melanomas are sometimes grouped together as nonmelanoma skin cancers because they tend to act very differently from melanomas.
Keratinocyte cancers are by far the largest group of nonmelanoma skin cancers. They are called keratinocyte carcinomas or keratinocyte cancers because, when seen under a microscope, their cells share some features of keratinocytes, the most abundant cell type of normal skin. The most common types of keratinocyte cancer are basal cell carcinoma and squamous cell carcinoma.
Basal Cell Carcinoma
Basal cell carcinoma is so named because the cells of these cancers resemble the cells in the lowest layer of epidermis, called the basal cell layer. About 8 out of 10 nonmelanoma skin cancers are basal cell carcinomas. They usually develop on sun-exposed areas, especially the head and neck. Basal cell carcinoma was once found almost exclusively in middle-aged or older adults. Now it is also being seen in younger adults, probably because they are spending more time in the sun with their skin exposed.
Basal cell carcinoma tends to be slow growing. It is very rare for a basal cell carcinoma to spread to lymph nodes or to distant parts of the body. However, if a basal cell carcinoma is left untreated, it can grow into nearby areas and invade the bone or other tissues beneath the skin.
After treatment, basal cell carcinoma can recur (come back) in the same place on the skin. People who have had basal cell carcinoma are also more likely to get new ones elsewhere on the skin. In as many as half of people who have one basal cell carcinoma, a new basal cell skin cancer will develop within 5 years.
Squamous Cell Carcinoma
About 2 out of 10 nonmelanoma skin cancers are squamous cell carcinomas. They commonly appear on sun-exposed areas of the body, such as the face, ears, neck, lips, and back of the hands. They can also develop in scars or skin ulcers. They sometimes start in actinic keratoses (described on page 11). Less often, they can form in the skin of the genital area.
Squamous cell carcinomas tend to be more aggressive than basal cell carcinomas. They are more likely to invade fatty tissues just beneath the skin and are more likely to spread to lymph nodes and/or distant parts of the body, although this is still uncommon.
Keratoacanthomas are fairly common growths that are found on sun-exposed skin. These tumors closely resemble squamous cell carcinomas, and many doctors consider them to be a type of squamous cell cancer. They typically appear as firm, round, flesh-colored or red papules that progress to smooth, shiny dome-shaped nodules. Although they may start out growing quickly, their growth usually slows down. Many keratoacanthomas shrink or even go away on their own over time without any treatment. But some continue to grow, and a few may even spread to other parts of the body. Their growth is often hard to predict.
Less Common Types of Skin Cancer
In addition to melanoma and keratinocyte cancers, there are other much less common types of skin cancer. These cancers are also nonmelanoma skin cancers, but they are quite different from keratinocyte cancers and are treated differently, so it is useful to consider them separately.
Other nonmelanoma skin cancers include the following:
Merkel cell carcinoma
Skin adnexal tumors
Various types of sarcomas
Together, these types account for less than 1% of nonmelanoma skin cancers.
Merkel cell carcinoma
Merkel cell carcinoma is an uncommon type of skin cancer that develops from neuroendocrine cells (hormone-making cells that resemble nerve cells) in the skin. They are most often found on the head, neck, and arms but can start anywhere. These cancers are thought to be caused in part by sun exposure and partly by Merkel cell polyomavirus (MCV), a common virus that usually causes no symptoms. In a small percentage of people with this infection, changes in the virus's DNA can lead to this form of cancer. About 8 out of 10 Merkel cell carcinomas are thought to be related to MCV infection.
Unlike basal cell and squamous cell carcinomas, Merkel cell carcinomas often come back after treatment and can spread to nearby lymph nodes. They can also spread to internal organs, which is uncommon for squamous cell carcinomas and even less common for basal cell carcinomas. Treatment of Merkel cell carcinoma is described in the section "How Are Basal and Squamous Cell Skin Cancers Treated?"
Kaposi sarcoma usually starts within the dermis but can also form in internal organs. Before the mid-1980s, this cancer was rare and found mostly in elderly people of Mediterranean descent. Kaposi sarcoma has become more common because it is more likely to develop in people with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS). For more information about Kaposi sarcoma, contact your American Cancer Society at 800-227-2345 and request the document Kaposi Sarcoma or visit our Web site, cancer.org.
Lymphomas are cancers that start in lymphocytes, a type of immune system cell. These immune system cells can be found in the bone marrow (the soft inner part of some bones), lymph nodes (bean-sized collections of immune system cells), the bloodstream, and some internal organs. The skin also contains a significant number of lymphocytes.
Although most lymphomas start in lymph nodes or internal organs, there are certain types of lymphoma that appear to begin mostly or entirely in the skin. Primary cutaneous lymphoma means "a lymphoma that starts in the skin." The most common type of primary cutaneous lymphoma is cutaneous T-cell lymphoma (CTCL). The most common type of CTCL is called mycosis fungoides. To learn more about cutaneous lymphoma, contact your American Cancer Society at 800-227-2345 to request the document Lymphoma of the Skin or visit our Web site, cancer.org.
Adnexal tumors start in the hair follicles or glands (such as sweat glands) of the skin. Malignant (cancerous) adnexal tumors are rare, but benign (noncancerous) adnexal tumors are common.
Sarcomas develop from connective tissue cells, usually in tissues deep beneath the skin. Much less often, they can develop in the skin's dermis and subcutis. Several types of sarcoma can develop in the skin, including dermatofibrosarcoma protuberans (DFSP) and angiosarcoma (a blood vessel cancer).
Precancerous and Preinvasive Skin Conditions
These conditions can develop into skin cancer or can be very early stages in the development of skin cancer.
Actinic keratosis (solar keratosis)
Actinic keratosis, also known as solar keratosis, is a precancerous skin condition caused by overexposure to the sun. Actinic keratoses are usually small (less than ¼ inch across), rough pinkish-red or flesh-colored spots. They are most common in middle-aged or older adults with fair skin and usually develop on the face, ears, back of the hands, and arms, although they can develop on other parts of the body that have been exposed to the sun. A person with one actinic keratosis usually develops many more.
Actinic keratoses are slow growing and usually do not cause any symptoms. It is possible for actinic keratoses to turn into keratinocyte cancers. Actinic keratoses often go away on their own, but they may come back.
Even though most actinic keratoses do not become cancers, they are a warning that your skin has suffered sun damage. Some actinic keratoses and other skin conditions that could be precancerous should be removed. Your doctor should regularly check any unusual or suspicious areas of skin for changes that could indicate cancer.
Squamous cell carcinoma in situ (Bowen disease)
Squamous cell carcinoma in situ, also called Bowen disease, is the earliest form of squamous cell skin cancer. "In situ" means that the cells of these cancers are still entirely within the epidermis and have not invaded the dermis.
Bowen disease appears as reddish patches. Compared with actinic keratoses, Bowen disease patches tend to be larger (sometimes more than ½ inch across), red, scaly, and sometimes crusted.
As with invasive squamous cell skin cancers, the main risk factor for Bowen disease is overexposure to the sun. Bowen disease of the anal and genital skin is often related to sexually transmitted infection with human papilloma viruses (HPVs), the viruses that can cause genital warts.
Benign Skin Tumors
Most tumors, or growths, of the skin are not cancerous and rarely, if ever, turn into cancers. These benign types of skin tumors include the following:
most types of 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 growths of benign fat cells)
warts (rough-surfaced growths caused by a virus)
What Are the Key Statistics About Basal and Squamous Cell Skin Cancers?
Cancer of the skin (including melanoma and basal and squamous cell skin cancers) is by far the most common of all types of cancer.
The number of people who develop basal and squamous cell skin cancers each year is not known for sure. Statistics of most other cancers are known because they are reported to cancer registries, but basal and squamous cell skin cancers are not reported. All the numbers presented here, therefore, are estimates.
About 2.2 million basal and squamous cell skin cancers are diagnosed each year. Most of these are basal cell cancers. Squamous cell cancers occur less often.
The number of these cancer diagnoses has been increasing for many years. This increase is probably due to a combination of increased detection, more sun exposure, and people living longer.
Death from these cancers is uncommon. It is thought that about 2,000 people die of nonmelanoma skin cancers each year. The death rate has dropped about 30% in the past 30 years. Most people who die are elderly. Other people more likely to die of skin cancer are those whose immune system is suppressed, such as people who have received organ transplants.CHAPTER 2
Risk Factors and Causes
What Are the Risk Factors for Basal and Squamous Cell Skin Cancers?
A risk factor is anything that affects your chance of a disease developing, such as cancer. Different types of cancer have different risk factors. For example, unprotected exposure to strong sunlight is a risk factor for skin cancer, and smoking is a risk factor for cancers of the lung, mouth, throat, kidneys, bladder, and several other organs.
Excerpted from Basal and Squamous Cell Skin Cancer by American Cancer Society. Copyright © 2012 American Cancer Society. Excerpted by permission of American Cancer Society / Health Promotions.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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