Cancer is not one disease, but many diseases that occur in different areas of  the body. Each type of cancer is characterized by the uncontrolled growth of  cells. Under normal conditions, cell reproduction is carefully controlled by the  body. However, these controls can malfunction, resulting in abnormal cell growth  and the development of a lump, mass, or tumor. Some cancers involving the blood  and blood-forming organs do not form tumors but circulate through other tissues  where they grow.

A tumor may be benign (non-cancerous) or malignant (cancerous). Cells from  cancerous tumors can spread throughout the body. This process, called  metastasis, occurs when cancer cells break away from the original tumor and  travel in the circulatory or lymphatic systems until they are lodged in a small  capillary network in another area of the body. Common locations of metastasis  are the bones, lungs, liver, and central nervous system.

The type of cancer refers to the organ or area of the body where the cancer  first occurred. Cancer that has metastasized to other areas of the body is named  for the part of the body where it originated. For example, if breast cancer has  spread to the bones, it is called “metastatic breast cancer� not bone  cancer.