What is Cancer?
What is Cancer?

During your lifetime, you or someone you know is likely to be diagnosed with one of the group of diseases known as cancer. Cancer cells are your own body’s cells growing uncontrollably. The resulting growth is called a tumor and may be life-threatening.

What happens to your body?
Cancer begins in the cells, the body's basic unit of life. Normal, healthy cells grow and divide under strict control. They replace themselves only when the body needs them. Many cells, like brain and muscle cells, are not able to divide and replace themselves in normal life. Others, like blood cells, grow and divide rapidly. If cells lose this strict control, they continue to grow and make new cells, forming growths called tumors.

Tumors compete with organs and tissues for food and space in the body. There are two major types of tumors: malignant (cancerous) and benign. Malignant tumors can break into other tissues and move to other places in the body. Benign tumors cannot move to other places in the body. Cancer is a general term referring to a malignant tumor.

Tumor cells can move through the body in the bloodstream and lymph channels. When a malignant tumor spreads to a different location in the body, it is called a metastasis.

What are the different kinds of cancers?
There are many kinds of cancers. In general, they fall into four main groups:

  • Carcinomas are the most common cancers. They begin in the cells that cover external and internal body surfaces. Lung, breast and colon cancer are the most frequently diagnosed carcinomas in the United States.
  • Sarcomas begin in the supporting tissues of the body. These tissues include bone, cartilage, fat, connective tissue and muscle.
  • Lymphomas arise in the lymph nodes and tissues of the body's immune system. Hodgkin’s Disease and non-Hodgkin’s Lymphoma are examples of lymphomas.
  • Leukemias are cancers of the blood-forming cells that grow in the bone marrow. These cells flow in large numbers through the bloodstream.

What are some symptoms of cancer?
Some signs or symptoms that might indicate cancer are listed below. See your doctor if you have any of the following:

  • Thickening or lump in the breast or any other part of the body
  • Obvious change in a wart or mole
  • A sore throat that does not heal
  • Nagging cough or hoarseness
  • Changes in bowel or bladder habits
  • Indigestion or difficulty swallowing
  • Unexplained changes in weight
  • Unusual bleeding or discharge

When these or other symptoms occur, they are not always caused by cancer. They may also be caused by infections, benign tumors, or other problems. It is important to see the doctor about any of these symptoms or about other physical changes. Only a doctor can make a diagnosis. One should not wait to feel pain: Early cancer usually does not cause pain.

To learn more:

What Is Cancer?
(National Cancer Institute)
This is a good place to begin learning about cancer. It tells you what cancer is, how it is diagnosed, and how it is treated. You can find out about possible causes and prevention and learn what to expect if you or someone you know has cancer. The section on "Preparing for Treatment" includes a list of questions to ask before treatment. Some medical terms are linked to definitions. This is long, but content titles on the left make it easy to find a part that interests you.
National Cancer Institute Understanding Cancer Series. Retrieved from:

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Written by: Nancy C. McKeehan, M.S.L.S.
Reviewed by: Jeffrey G. Schultze, M.D.
Last Modified: Tuesday February 17, 2015 2:45 PM