Cancer Terms Listed
Cancer is a group of many related diseases that begin
in cells, the body's basic unit of life. To understand
cancer, it is helpful to know what happens when normal
cells become cancerous.
The body is made up of many types of cells.
Normally, cells grow and divide to produce more cells
only when the body needs them. This orderly process helps
keep the body healthy. Sometimes, however, cells keep
dividing when new cells are not needed. These extra cells
form a mass of tissue, called a growth or tumor.
Tumors can be benign or malignant.
Benign tumors are not cancer. They can often
be removed and, in most cases, they do not come back.
Cells from benign tumors do not spread to other parts
of the body. Most important, benign tumors are rarely
a threat to life.
Malignant tumors are cancer. Cells in these
tumors are abnormal and divide without control or order.
They can invade and damage nearby tissues and organs.
Also, cancer cells can break away from a malignant tumor
and enter the bloodstream or the lymphatic system. That
is how cancer spreads from the original cancer site to
form new tumors in other organs. The spread of cancer
is called metastasis.
Leukemia and lymphoma are cancers that arise
in blood-forming cells. The abnormal cells circulate in
the bloodstream and lymphatic system. They may also invade
(infiltrate) body organs and form tumors.
Most cancers are named for the organ or type of cell in
which they begin. For example, cancer that begins in the
lung is lung cancer, and cancer that begins in cells in
the skin known as melanocytes is called melanoma.
When cancer spreads (metastasizes), cancer
cells are often found in nearby or regional lymph nodes
(sometimes called lymph glands). If the cancer has reached
these nodes, it means that cancer cells may have spread
to other organs, such as the liver, bones, or brain. When
cancer spreads from its original location to another part
of the body, the new tumor has the same kind of abnormal
cells and the same name as the primary tumor. For example,
if lung cancer spreads to the brain, the cancer cells
in the brain are actually lung cancer cells. The disease
is called metastatic lung cancer (it is not brain cancer).