Cancer is the abnormal growth of cells that causes illness in the body. Cells are the tiny units that make up all living things. Humans are made of over 10 trillion of them! You can't see cells with your eyes alone, but you can under a high-powered microscope.

Cancer happens when cells start growing abnormally and dividing out of control. A group or mass of growing cells is called a tumor. A tumor in any part of the body is called benign (say: bih-nine) if it's not cancer, or malignant (say: meh-lig-nent) if it is cancer.

Kids don't get cancer very often. And many of those who do get it can be treated and cured. Common cancer treatments include chemotherapy, which means getting anti-cancer drugs through an IV, and radiation, which means powerful energy waves (like X-rays) are used to kill cancer cells. Surgery also might be done to remove tumors. And in some cases, such as leukemia, a bone marrow or stem cell transplant might be done to help a kid be healthy again.

Here are a few types of cancer that kids can get:

Leukemia

Leukemia (say: loo-kee-mee-uh) is the most common type of cancer kids get, but it is still very rare. Leukemia involves the blood and blood-forming organs, such as the bone marrow. Bone marrow is the innermost part of some bones where blood cells are first made. A kid with leukemia produces lots of abnormal white blood cells in the bone marrow.

Usually, white blood cells fight infection, but the white blood cells in a person with leukemia don't work the way they're supposed to. Instead of protecting the person, these abnormal white blood cells multiply out of control. They fill up the bone marrow and make it hard for enough normal, infection-fighting white blood cells to form.

Other blood cells - such as red blood cells (which carry oxygen in the blood to the body's tissues) and platelets (which allow blood to clot) - also get crowded out by the white blood cells of leukemia. These cancer cells may move to other parts of the body, including the bloodstream, liver, spleen, and lymph nodes. In those areas, cancer cells can continue to multiply and build up.

Brain Cancer

A brain tumor is a group or clump of abnormally growing cells that can be found in or on the brain. They're rare in kids. Of the more than 73 million kids and teens in the United States, about 3,100 are diagnosed with brain tumors every year.

Brain tumors can either start in the brain or spread there from another part of the body - some cancers that start in other parts of the body may have cells that travel to the brain and start growing there.

Lymphoma

Lymphoma (say: lim-foe-mah) is a general term for a group of cancers that start in the body's lymphatic (say: lim-fah-tik) system. The lymphatic system is made of hundreds of bean-size lymph nodes - also sometimes called glands - that work to fight off germs or other foreign invaders in the body. Lymph nodes are found throughout the body. When we get colds or the flu, we can sometimes feel our lymph nodes along the front of the neck or under the jaw. That's because when the body is fighting off these germs, the lymph nodes grow larger. The spleen, an organ in your stomach that filters blood, and the thymus (say: thigh-mes), a gland in the upper chest, also are parts of the lymphatic system.

Lymphoma happens when a lymphocyte (say: lim-foe-site), a type of white blood cell, begins to multiply and crowd out healthy cells. The cancerous lymphocytes create tumors (masses or lumps of cancer cells) that enlarge the lymph nodes.

Getting Better

As doctors and researchers learn more about cancer, they're discovering better medicines and more successful ways of fighting it. The goal of cancer treatment is to kill or remove all the cancerous cells so healthy cells can take over again. When this happens, kids start feeling better and the people who care about them are relieved and happy.

Reviewed by: Donna Patton, MD
Date reviewed: August 2005
Originally reviewed by: Steven Dowshen, MD, and Michael Trigg, MD