Malignancy
Malignancy was a quality pertaining to tumors (cancerous), that could invade and destroy nearby tissue, and that may spread (metastasize) to other parts of the body.
In 2151, Doctor Phlox discovered that the malignancy of Nadet's interstitial tumors has spread to her lymphatic system, but cured her with cytolytic injections. (ENT: "Terra Nova")