Malignancy

n. state or quality of being malignant, hostility, desire to inflict harm or evil on another; malignant tumor, life-threatening tumor

Cancer is a group of diseases in which cells are aggressive (grow and divide without respect to normal limits), invasive (invade and destroy adjacent tissues), and/or metastatic (spread to other locations in the body). These three malignant properties of cancers differentiate them from benign tumors, which are self-limited in their growth and do not invade or metastasize (although some benign tumor types are capable of becoming malignant). Cancer may affect people at all ages, even fetuses, but risk for the more common varieties tends to increase with age. Cancer causes about 13% of all deaths. Apart from people, forms of cancer may affect animals and plants.
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Malignancy /ma·lig·nan·cy/ 1. a tendency to progress in virulence. 2. the quality of being malignant. 3. [more]Malignancy - Community and Resources

Noun
1. (medicine) a malignant state; progressive and resistant to treatment and tending to cause death
(synonym) malignance
(hypernym) disease
(hyponym) malignant tumor, malignant neoplasm, metastatic tumor
(part-meronym) cancer cell
(classification) medicine, medical specialty
2. quality of being disposed to evil; intense ill will
(synonym) malignity, malignance
(antonym) benignity, benignancy, graciousness
(hypernym) evil, evilness
(attribute) malign

(n.)
Virulence; tendency to a fatal issue; as, the malignancy of an ulcer or of a fever.
  

(n.)
Unfavorableness; evil nature.
  

(n.)
The state or quality of being malignant; extreme malevolence; bitter enmity; malice; as, malignancy of heart.
  

(n.)
The state of being a malignant.