What is cancer? Cancer affects 1 in 3 people in the United States. It is likely that you or someone you know has cancer. Here is some information to help you better understand what cancer is. You are made up of trillions of cells that normally grow and divide as needed throughout your life.When cells are abnormal or old, they usually die. Cancer begins when something goes wrong in this process and your cells keep making new cells and the old or abnormal ones don't die when they should. When cancer cells get out of control, they can crowd out normal cells. This makes it difficult for the body to function as it should. Cancer can be successfully treated in many people. It use to have no known cures iin the past. In fact, more people than ever before are living full lives after cancer treatment. Cancer is more than a disease There are many types of cancer. Cancer can occur anywhere in the body and is named after the part of the body where it originated. For example, breast cancer that starts in the breast is still called breast cancer even if it has spread (metastasized) to other parts of the body. There are two broad categories of cancer: Hematologic (blood) cancer is cancer of the blood cells, including leukemia, lymphoma, and multiple myeloma. Solid tumor Tumors are tumors of any other organ or tissue in the body. The most common solid tumors are breast, prostate, lung and colon cancer.