"Cancer" is a condition in which body cells reproduce much more rapidly than happens normally. When body cells are changed through exposure to substances, through infection by viruses, or through genetic mutations, the result may be an accelerated rate of growth. This accelerated rate of growth results in the formation of a "tumor," a mass of cells that are, in some way, different from the normal cell structure.
A benign tumor is a type of cancer in which the growth of cells is limited to one area in the body. Benign tumors can usually be surgically removed and cause no changes or impacts to other areas or systems of the body.
A malignant tumor indicates a type of cancer in which the changed cells have spread to other parts of the body, causing changes in other types of cells and in other systems or organs than the original area. Malignant tumors are much more serious because of the potential for widespread impact throughout the body, requiring more types of treatment to address different areas and issues.