Clinical Definition

A tumor is any kind of swelling or enlargement of tissues involving abnormal growth anywhere in the body. A tumor can be cancerous or noncancerous (benign). However, benign tumors can still cause problems.

In Our Own Words

A tumor is an abnormal growth. Normally, cells in your body grow, divide and then die. In adults, cells normally divide in order to replace worn out or dying cells or to repair injuries. However, when the process goes wrong, new cells can form even if your body does not need them. Old cells may not die off in an orderly fashion. When this occurs, the extra cells can form an abnormal mass (tumor).

In most types of cancer, the cancer cells form a tumor; leukemia is an exception. When cancer cells travel to other parts of the body, they grow and form new tumors there, a process known as metastasis.