Cancer is a group of more than 100 different diseases that have some important things in common. All types of cancer affect our cells, the body's basic unit of life. To understand cancer, it's important to know how normal cells become cancerous. Normally, cells grow, divide and produce more cells to keep the body healthy and functioning properly. The mass of extra cells forms a growth or tumor.
Tumors can be benign or malignant.
Benign tumors are not cancerous. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body, and they are not life threatening. Malignant tumors are cancerous. Cells in malignant tumors are abnormal and divide without control or order.