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What is
Cancer?
Cancer is a group of many
different diseases that have some important things in common.
They all arise in cells, the body's basic unit of life. To
understand different types of cancer, it is helpful to know
about normal cells and what happens when they 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 cells keep dividing
when new cells are not needed. These cells may form a mass of
extra tissue called a
growth or tumor.
Tumors can be benign
or malignant.
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Benign tumors
are not cancer. They can usually be removed, and in most
cases, they don't come back. Most important, the cells in
benign tumors do not invade other tissues and do not
spread to other parts of the body. Benign breast tumors
are not a threat to life.
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Malignant tumors
are cancer. Cells in these tumors can invade and damage
nearby tissues and organs. Also, cancer cells can break
away from a malignant tumor and enter the bloodstream or lymphatic
system. That is how breast cancer spreads and
forms secondary tumors in other parts of the body. The
spread of cancer is called metastasis.
This booklet deals with
breast cancer. For more information about benign breast lumps
and other benign breast changes, read NCI's booklet, Understanding
Breast Changes: A Health Guide for All Women, which is
available from the Cancer Information Service at
1-800-4-CANCER
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