What is cancer?

Cancer is the growth and spread of abnormal cells. Normal cells grow, divide, and die in an orderly fashion. During growth and development, they divide more rapidly, but in adults they divide only to replace worn-out or dying cells and to repair injuries. Cancer cells, however, do not behave like normal cells. They continue to grow and divide, forming masses of abnormal cells, called tumors. These masses can compress normal cells and interfere with their ability to function. Not all tumors are cancerous, but if they do become cancerous, or malignant, cells can break off and travel through the bloodstream or the lymph system to other areas of the body. This is called metastasis, and once this happens, cancer is no longer curable. Cancer is named after the part of the body where it began.