Cancer is the catchall term applied to diseases caused by the uncontrolled growth of abnormal cells. Cancer isn't one disease. It is many different diseases, more than 100 and counting.
Each kind of cancer is usually named for the cell type in which it begins — cancer that starts in a lung is called lung cancer; cancer that starts in pigment cells in the skin, which are known as melanocytes, is called melanoma.
When detected and treated early, cancer can often be stopped. That said, cancer is a leading cause of death and disability around the world.
What Is It?
A brain tumor is a mass of abnormally growing cells in the brain or skull. It can be benign (noncancerous) or malignant (cancerous). Unlike other cancers, a cancer arising from brain tissue (a primary brain cancer) rarely spreads. Whether benign or malignant, all brain tumors are serious. A growing tumor eventually will compress and damage other structures in the brain.
There are two categories of brain tumors: primary and secondary. Primary tumors start in brain tissue, while secondary tumors spread to the brain from another area of the body. Primary tumors are classified by the tissue in which they begin:
Gliomas, the most common primary tumors, start in the brain's glial (supportive) tissue. There are several types of gliomas, and they can vary in their aggressiveness and response to treatment. Glioblastoma multiforme is a fast-growing, higher-grade tumor that can arise from a lower-grade glioma.
Medulloblastomas come from early embryonic cells and more commonly occur in children.
Meningiomas are related to cells in the membranes surrounding the brain and spinal cord. They are usually benign, but can come back (recur) after treatment.
Secondary tumors most commonly arise from the lungs or breast. Other cancers, especially melanoma (a type of skin cancer), renal cell cancer (a type of kidney cancer), and lymphoma (a cancer of the immune system) can spread to the brain. When this happens, the cancer is the same as the original cancer. For example, lung cancer that spreads to the brain is known as metastatic lung cancer, because the tumor's cells resemble abnormal lung cells. Secondary brain tumors are much more common than primary tumors.
Although brain tumors can occur at any age, they most commonly affect adults 40 to 70 years old and children 3 to 12 years of age. Whether the use of cellular phones contributes to the development of brain tumors, especially in children, has sparked debate. The issue is far from resolved, and additional research is needed.
Lymphoma is a cancer of the lymph (or lymphatic) system. It is part of the immune system. It collects and destroys invading organisms, such as bacteria and viruses, and abnormal cells. It protects the body from infection and disease.
Lymphedema is the buildup of fluid called lymph in the tissues under your skin when something blocks its normal flow. This causes swelling, most commonly in an arm or leg.
Lymph normally does an important job for your body. It carries foreign material and bacteria away from your skin and body tissues, and it circulates infection-fighting cells that are part of your immune system.
Lymphedema occurs when there is inadequate lymph drainage from the body, usually from a blockage in a lymph channel. Lymphatic fluid builds up underneath the skin and causes swelling. Most commonly lymphedema affects the arms or legs.
Swelling from lymphedema can look similar to the more common edema caused by leakage from tiny blood vessels under the skin.
In most cases of lymphedema, the lymphatic system has been injured so that the flow of lymph is blocked either temporarily or permanently. This is called secondary lymphedema. Common causes include:
Surgical damage — Surgical cuts and the removal of lymph nodes can interfere with normal lymph flow. Sometimes, lymphedema appears immediately after surgery and goes away quickly. In other cases, lymphedema develops from one month to 15 years after a surgical procedure. Lymphedema occurs quite often in women who have had multiple lymph nodes removed during surgery for breast cancer.
An infection involving the lymphatic vessels — An infection that involves the lymphatic vessels can be severe enough to cause lymphedema. In areas of the tropics and subtropics, such as South American, the Caribbean, Africa, Asia and the South Pacific, parasites are a common cause of lymphedema. Filariasis, a parasitic worm infection, blocks the lymph channels and causes swelling and thickening below the skin, usually in the legs.
Cancer — Lymphoma, a cancer that starts in the lymph nodes, or other types of cancer that spread to the lymph nodes may block lymph vessels.
Radiation therapy for cancer — This treatment can cause scar tissue to develop and block the lymphatic vessels.
When lymphedema occurs without any known injury or infection, it is called primary lymphedema. Doctors diagnose three types of primary lymphedema according to when symptoms first appear:
At birth — Also known as congenital lymphedema. Risk is higher in female newborns. The legs are affected more often than the arms. Usually both legs are swollen.
After birth but before age 36 — Usually, it is first noted during the early teenage years. This is the most common type of primary lymphedema.
Age 36 and older — This is the rarest type of primary lymphedema.
All three types of primary lymphedema are probably related to the abnormal development of lymph channels before birth. The difference is when in life they first cause swelling of the legs or arms.
Leukemia is a form of cancer that affects the body's ability to make healthy blood cells. It starts in the bone marrow, the soft center of various bones. This is where new blood cells are made. Blood cells include
Red blood cells, which carry oxygen from the lungs to the body's tissues and take carbon dioxide to the lungs to be exhaled
Platelets, which help blood clot
White blood cells, which help fight infections, viruses, and diseases.
Although cancer can affect red blood cells and platelets, leukemia generally refers to cancer of the white blood cells. The disease usually affects one of the two major types of white blood cells: lymphocytes and granulocytes. These cells circulate throughout the body to help the immune system fight off viruses, infections, and other invading organisms. Leukemias arising from lymphocytes are called lymphocytic leukemias; those from granulocytes are called myeloid, or myelogenous, leukemias.
A bone marrow transplant is a procedure used to treat certain types of cancer and some other diseases. Before the bone marrow transplant takes place, a person's bone marrow cells are destroyed with radiation or chemotherapy.
The cells that normally live in the bone marrow and that are responsible for making blood cells are then replaced. Bone marrow cells are blood cells that are located in the spongy center of bones.
Acute lymphocytic leukemia (ALL) is a cancer of the body's blood-making system. (It is also known as acute lymphoblastic leukemia and acute lymphoid leukemia.) The word "acute" refers to the fact that the disease can progress quickly. "Lymphocytic" means that the cancer develops from lymphocytes, a type of white blood cell.
Bone marrow, the soft inner part of bones, makes cells that circulate in the blood. They include white blood cells, red blood cells, and platelets. The two major types of white blood cells are myeloid cells and lymphoid cells. Lymphocytes form from lymphoid cells.
Normally, the bone marrow makes three types of infection-fighting lymphocytes:
B lymphocytes — These cells make antibodies to help protect the body from germs.
T lymphocytes — These cells can destroy virus-infected cells, foreign cells, and cancer cells. They also help make antibodies.
Natural killer cells — These cells can also kill cancer cells and viruses.
In ALL, the bone marrow makes too many immature lymphocytes. These lymphocytes, called blasts, contain abnormal genetic material. They cannot fight infections as well as normal cells. In addition, because these lymphocytes multiply quickly, they crowd out healthy white blood cells, red blood cells, and platelets in the blood and bone marrow. This may lead to infection, anemia, and easy bleeding.
ALL typically invades the blood quickly. It can involve other parts of the body, such as the lymph nodes, liver, spleen, brain and spinal cord (central nervous system), and testicles (testes).
Although it is rare, ALL is the most common cancer in children. It can affect children of any age, but most are diagnosed between 2 and 4 years old.
A few factors may increase a child's risk of developing ALL. These include
having a sibling with leukemia
exposure to x-rays before birth
exposure to radiation
past treatment with chemotherapy or other drugs that weaken the immune system
having certain inherited disorders, such as Down syndrome
having a specific genetic change (mutation).
Having one or more of these risk factors does not mean your child will develop ALL. Many children with the disease have no risk factors.
ALL has several subtypes. Subtypes depend on
whether the cancerous cells formed from B lymphocytes or T lymphocytes
your child's age
whether the cells have certain changes in their genetic material.
Acute lymphocytic leukemia (ALL) is a type of leukemia. Leukemia is a cancer of the blood or bone marrow. ALL is also known as acute lymphoblastic leukemia and acute lymphoid leukemia.
ALL is acancer of the body's blood-making system. Blood cells are produced in the bone marrow, the soft, inner part of bones.
The word "acute" in acute lymphocytic leukemia refers to the fact that the disease can progress quickly. The word "lymphocytic" means that the cancer develops from lymphocytes, a type of white blood cell.
The body produces three types of infection-fighting lymphocytes:
B lymphocytes, which make antibodies to help protect the body from germs.
T lymphocytes, which can destroy virus-infected cells, foreign cells, and cancer cells.
Natural killer cells, which also can kill cancer cells and viruses.
In ALL, the body produces too many immature lymphocytes (lymphoblasts). These cells cannot fight infection as well as normal cells.
In addition, as these lymphocytes quickly multiply, they crowd out healthy white blood cells, red blood cells, and platelets in the blood and bone marrow. This may lead to infection, anemia, and easy bleeding.
Certain genetic changes are also associated with ALL.
Acute lymphocytic leukemia typically invades the blood quickly. It can involve other parts of the body, such as the lymph nodes, liver, spleen, brain and spinal cord (central nervous system), and testes.
Chronic lymphocytic leukemia (CLL) is a cancer that occurs when the bone marrow makes too many lymphocytes, a type of white blood cell. CLL usually grows slowly compared to other leukemias, and it may not cause symptoms for some time.
CLL is one of four main types of leukemia. It is the second most common type of leukemia in adults; most people with CLL are middle-aged or older. The disease is very rare in children.
Normally, a person's immature blood stem cells develop into myeloid and lymphoid stem cells. The myeloid cells become mature blood cells: white blood cells, red blood cells, and platelets. Lymphoid stem cells develop into three types of infection-fighting lymphocytes:
B lymphocytes, which make antibodies to help protect the body from germs
T lymphocytes, which can destroy virus-infected cells, foreign cells, and cancer cells
Natural killer cells, which also can kill cancer cells and viruses.
In CLL, too many blood stem cells turn into abnormal lymphocytes. These cells do not function properly. Even in high numbers, they cannot fight infection as well as normal cells. As they pile up in the blood and bone marrow, they crowd out healthy white blood cells, red blood cells, and platelets. This can result in infection, anemia, and easy bleeding. CLL most often develops from B lymphocytes.
CLL begins in the bone marrow but then typically invades the blood. In time, it can spread to other parts of the body that normally contain lymphocytes, such as the lymph nodes (in the neck, abdomen, and groin, under the arms, and around the collarbone), as well as the liver and the spleen. These tissues may then become enlarged.
Certain factors may increase a person's chance of developing CLL. These include
having relatives with CLL or cancer of the lymph system
being exposed to certain chemicals
being middle-aged or older
being male and white
being of North American or European descent.
Keep in mind, however, that having one or more risk factors for CLL does not mean you will develop the disease.
One of the most common cancers, lung cancer usually occurs when a cancer-causing agent, or carcinogen, triggers the growth of abnormal cells in the lung. These cells multiply out of control and eventually form a tumor. As the tumor grows, it can block or narrow airways and make breathing difficult. Eventually, tumor cells can spread (metastasize) to nearby lymph nodes and other parts of the body. These include the
In most cases, the carcinogens that trigger lung cancer are chemicals found in cigarette smoke. However, more and more lung cancers are being diagnosed in people who have never smoked.
Lung cancers are divided into two groups: non-small cell lung cancer (NSCLC) and small cell lung cancer. NSCLC accounts for about 85% of all lung cancers. These cancers are further divided into subgroups, based on how their cells look under a microscope:
Adenocarcinoma. This is the most common type of NSCLC. Although it is related to smoking, it is the most common type of lung cancer in nonsmokers. It is also the most common form of lung cancer in women and in people younger than 45. It usually develops near the edge of the lung. It can also involve the pleura, the membrane covering the lung.
Squamous cell carcinoma. This type of NSCLC tends to form a mass near the center of the lungs. As the mass gets larger, it can bulge into one of the larger air passages, or bronchi. In some cases, the tumor forms a cavity in the lungs.
Large cell carcinoma. Like adenocarcinoma, large cell carcinoma tends to develop at the edge of the lungs and spread to the pleura. Like squamous cell carcinoma, it can form a cavity in the lungs.
Adenosquamous carcinoma, undifferentiated carcinoma, and bronchioloalveolar carcinoma. These are relatively rare NSCLCs.
NSCLC is more likely than small cell cancer to be localized at the time of diagnosis. That means the cancer is limited to the lung or that it hasn't spread beyond the chest. As a result, it can usually be treated with surgery. It may not respond well to chemotherapy (anticancer drugs). However, sophisticated genetic tests can help predict which patients may show favorable responses to particular treatments, including chemotherapy.
Unfortunately, even when doctors think that the cancer is localized, it often comes back after surgery. This means cancer cells had started to spread before surgery, but they couldn't yet be detected.
Your risk of all types of lung cancer, including NSCLC, increases if you
smoke. Smoking cigarettes is by far the leading risk factor for lung cancer. In fact, cigarette smokers are 13 times more likely to develop lung cancer than nonsmokers. Cigar and pipe smoking are almost as likely to cause lung cancer as cigarette smoking.
breathe tobacco smoke. Nonsmokers who inhale fumes from cigarette, cigar, and pipe smoking have an increased risk of lung cancer.
are exposed to radon gas. Radon is a colorless, odorless radioactive gas formed in the ground. It seeps into the lower floors of homes and other buildings and can contaminate drinking water. Radon exposure is the second leading cause of lung cancer. It's not clear whether elevated radon levels contribute to lung cancer in nonsmokers. But radon exposure does contribute to lung cancer in smokers and in people who regularly breathe high amounts of the gas at work (miners, for example). You can test radon levels in your home with a radon testing kit.
are exposed to asbestos. Asbestos is a mineral used in insulation, fireproofing materials, floor and ceiling tiles, automobile brake linings, and other products. People exposed to asbestos on the job (miners, construction workers, shipyard workers, and some auto mechanics) have a higher-than-normal risk of lung cancer. People who live or work in buildings with asbestos-containing materials that are deteriorating also have an increased risk of lung cancer. The risk is even higher in people who also smoke. Asbestos exposure also increases the risk of developing mesothelioma, a relatively rare and usually fatal cancer. It usually starts in the chest and resembles lung cancer.
are exposed to other cancer-causing agents at work. These include uranium, arsenic, vinyl chloride, nickel chromates, coal products, mustard gas, chloromethyl ethers, gasoline, and diesel exhaust.
Stomach cancer, also called gastric cancer, is the uncontrolled growth of abnormal cells that form the inner lining of the stomach. The disease often does not cause symptoms until its later stages. Usually, by the time stomach cancer is diagnosed, the prognosis is poor. Most people who are diagnosed with stomach cancer are over age 60. The disease rarely occurs before age 50.