What is cancer?
Cancer is a group of many related diseases that involve abnormal
growth and spread of cells. When abnormal cells grow they frequently
form lumps called tumors. Not all tumors are malignant. Some cells
stay contained in benign, or harmless, tumors. In other cases, cancer
cells in malignant tumors can break off and spread via the blood
and lymph systems to other parts of the body in a process known
as metastasis. These metastases can then create new tumor sites
in other parts of the body.
Half of all men and one-third of all women in the US will develop
cancer in their lifetimes.
What causes cancer?
The causes of cancer are complex and often involve a combination
of lifestyle or environmental factors. For example, smoking and
diet can affect a person's likelihood of getting cancer, as can
prolonged exposure to certain chemicals and other substances called
carcinogens. Some people are genetically predisposed to certain
types of cancer.