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.