Cancer is defined as the uncontrolled growth of abnormal cells derived from normal tissues. Our bodies depend on cells as the building blocks of life.
Cells make up or comprise tissues.
Tissues are combined to make organs. Organs in turn make up organ systems. Lastly, organ systems make the body. Tissues in the body will naturally lose cells over time, so replacement of the old cells is necessary. When cells fail to develop or mature properly, they may become abnormal or cancerous.