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.