What Is Cancer?
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. Cancer that has spread is called
metastatic cancer.
Most cancers are named for the organ or type of cell in which
they begin. 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 (not brain cancer).
Children can get cancer in the same parts of the body as adults
do, but some types of cancer are more common in children. The
most common form of childhood cancer is
leukemia. Leukemia is
cancer of the blood. It develops in the
bone marrow, which is a
spongy substance that fills the inside of the bones and makes
blood cells. Other cancers often found in children are brain
tumors, childhood
lymphomas, Hodgkin's disease, Wilms'
tumors, neuroblastomas, osteogenic sarcomas, Ewing's sarcomas,
retino-blastomas, rhabdomyosarcomas and hepatoblastomas. The
Appendix contains information on the major types of
childhood cancer.
Children's cancers do not always act like, get treated like, or
respond like adult cancers. Avoid reading about adult cancer to
learn about your child's prognosis. Childhood cancers can occur
suddenly, without early symptoms, and have a high rate of cure.
You can find more details about these types of cancer in other
National Cancer Institute (NCI) booklets. NCI's What You Need to
Know About... brochures have information about specific types of
cancer. (See page 96 for more information on available booklets.)
To receive copies from the NCI-supported Cancer Information
Service (CIS), call 1-800-4-CANCER (1-800-422-6237) or TTY at
1-800-332-8615. Also, many NCI publications may be viewed or
ordered on the Internet at http://cancer.gov/publications.
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