A tumor is an abnormal and functionless mass of tissue within a living body that is not inflammatory and arises from pre-existent tissue. This can either be benign (non-cancer) or malignant (cancer). Malignant tumors (cancer) are more invasive and can spread (metastasize) to other parts of the body. According to the National Center for Health Statistics, cancer was (as of 2004) the second leading cause of death in the United States. Inside the body, even benign tumors can cause harm, for example, by occupying space or exerting pressure on adjacent organs or tissues.