What is a tumor?

Tumors, which are lumps of tissue, can be cancerous (malignant) or not cancerous (benign).

• Cancerous tumors spread into or invade nearby tissues and can travel to distant places in the body to form new tumors (a process called metastasis). Even when removed, these tumors sometimes grow back.
• Benign tumors do not spread into or invade nearby tissue, and usually don’t grow back when removed. Benign tumors can sometimes be quite large, however, and some can cause serious symptoms or be life-threatening, such as benign tumors in the brain.