A tumor is a swollen, organ-like mass of abnormal tissue. Tumors come in two types: Benign, which do not spread to other tissues, and Malignant (AKA Cancerous), which spreads throughout the body, devouring normal, healthy tissue and absorbing nutrients to fuel its growth. It can also be used as a mocking descriptor of a badly drawn muscular character or hypertrophied organ.

Tumors form when a cell comes down with a case of the stupids and forgets how to stop deviding. They do not undergo Apoptis, which is the natural death and recycling of old or damaged cells. Therefore, they undergo Necrosis (decay) upon cell-death instead. This, of course, is terrible for the body.