Cancer (medical term: malignant neoplasm) is a class of disease in which a group of cells display uncontrolled growth, invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasize (spread to other locations in the body).
These three malignant properties of cancer differentiate them from benign tumors, which are self-limited, and do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not.
Cancer may affect people at all ages, even fetuses, but the risk for most varieties increases with age. Cancer causes about 13 percent of all human deaths.