Cancer is a disease in which cells change and grow at a rate that is out of control.
Cells are the smallest parts of our bodies that are complete living units.
Usually, our cells divide in a predictable way, replacing old cells. When DNA becomes damaged, the body has special tumor-suppressing genes that usually can control the problem cells. The DNA signals the cells to multiply rapidly. The cells form a lump called a cancer. A cancerous tumor is called malignant.