Malignant

A tumor or cancer is classified as malignant (as opposed to benign), when it exhibits any one or more of three characteristics:
*Anaplasia - where cells stop being differentiated into functional cells and to start merely replicating without limit
*Invasiveness - where the cells invade other tissues and organs, extending their boundaries without limit
*Metastasis - where cells from the tumor or cancer can travel through the bloodstream or other systems to start growing new tumors
A malignant tumor or cancer will always result in the death of the patient without treatment, and may be terminal even with aggressive treatment.
Malignancy at Wikipedia
Category:Medical terminology