This animation shows how a tumor forms, recruits blood vessels, and enters metastasis.

A tumor consists of cells that are dividing at an abnormally high rate. These cells compete with normal cells for resources and may even invade tissues where they do not belong. As shown in the animation, tumors can recruit blood vessels from surrounding tissues and spread cancerous cells to other parts of the body. Left unchecked, tumors may interfere with the body's normal function, destroy organs, and eventually kill the organism.

Depending on students’ backgrounds, it may be helpful to pause the animation at various points to discuss different features or steps in the progression of the tumor.