The term "malignancy" refers to the presence of cancerous cells that have the ability to spread to other sites in the body (metastasize) or to invade nearby (locally) and destroy tissues. Malignant cells tend to have fast, uncontrolled growth and do not die normally due to changes in their genetic makeup.
Malignant cells that are resistant to treatment may return after all detectable traces of them have been removed or destroyed.
National Cancer Institute website. NCI dictionary of cancer terms. www.cancer.gov/publications/dictionaries/cancer-terms/def/malignancy. Accessed October 14, 2020.
Park BH. Cancer biology and genetics. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 171.