What Is Cancer? - NCI

Differences between Cancer Cells and Normal Cells

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Cancer cells differ from normal cells in many ways. For instance, cancer cells:

• grow in the absence of signals telling them to grow. Normal cells only grow when they receive such signals.
• ignore signals that normally tell cells to stop dividing or to die (a process known as programmed cell death, or apoptosis).
• invade into nearby areas and spread to other areas of the body. Normal cells stop growing when they encounter other cells, and most normal cells do not move around the body.
• tell blood vessels to grow toward tumors. These blood vessels supply tumors with oxygen and nutrients and remove waste products from tumors.
• hide from the immune system. The immune system normally eliminates damaged or abnormal cells.
• trick the immune system into helping cancer cells stay alive and grow. For instance, some cancer cells convince immune cells to protect the tumor instead of attacking it.
• accumulate multiple changes in their chromosomes, such as duplications and deletions of chromosome parts. Some cancer cells have double the normal number of chromosomes.
• rely on different kinds of nutrients than normal cells. In addition, some cancer cells make energy from nutrients in a different way than most normal cells. This lets cancer cells grow more quickly.

Many times, cancer cells rely so heavily on these abnormal behaviors that they can’t survive without them. Researchers have taken advantage of this fact, developing therapies that target the abnormal features of cancer cells. For example, some cancer therapies prevent blood vessels from growing toward tumors, essentially starving the tumor of needed nutrients.

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