What is Cancer?

There are many types of cancer. It’s not just one disease. Cancer can start in the lungs, the breast, the colon, or even in the blood. Cancers are alike in some ways, but they are different in the ways they grow and spread.

The cells in our bodies all have certain jobs to do. Normal cells divide in an orderly way. They die when they are worn out or damaged, and new cells take their place. Cancer is when the cells start to grow out of control. The cancer cells keep on growing and making new cells. They crowd out normal cells. This causes problems in the part of the body where the cancer started.

Cancer cells can also spread to other parts of the body. For instance, cancer cells in the lung can travel to the bones and grow there. When cancer cells spread, it’s called metastasis (meh-TAS-tuh-sis). When lung cancer spreads to the bones, it’s still called lung cancer. To doctors, the cancer cells in the bones look just like the ones from the lung. It’s not called bone cancer unless it started in the bones.

Some cancers grow and spread fast. Others grow more slowly. They also respond to treatment in different ways. Some types of cancer are best treated with surgery; others respond better to drugs called chemotherapy (key-mo-THER-uh-pee). Often 2 or more treatments are used to get the best results.

When someone has cancer, the doctor will want to find out what kind of cancer it is. People with cancer need treatment that works for their type of cancer.

Written by:

The American Cancer Society medical and editorial content team