Most often several changes in different genes contribute to cause a cancer to develop and progress. Cancers can be described as either benign or malignant. Benign cancers tend to stay in a single part of the body without spreading. This process of spreading from an original tumor to another part of the body is known as metastasis. A tumor can metastasize through the blood stream or through the lymphatic vessels of the body.
Cancers can develop from any normal part of the body.
The tissue type from which a cancer develops as well as the underlying genetic changes associated with the cancer largely determines the behavior of cancer. Considerable progress has been made in our understanding of the causes of cancer. A current explanation for the uncontrolled growth of cells that characterizes cancer is the loss of a cancer cell's ability to die. Normal cells in our bodies, and in the bodies of our pets, must be able to die if they become damaged. It has been recognized that cancer cells actually lose the ability to die and for this reason begin to grow uncontrollably.