Malignancy (from Latin male, meaning "badly", and -gnus, meaning "born") is the tendency of a medical condition to become progressively worse.
Malignancy is most familiar as a characterization of cancer. A malignant tumor contrasts with a non-cancerous benign tumor in that a malignancy is not self-limited in its growth, is capable of invading into adjacent tissues, and may be capable of spreading to distant tissues. A benign tumor has none of those properties.
Malignancy in cancers is characterized by anaplasia, invasiveness, and metastasis.[1] Malignant tumors are also characterized by genome instability, so that cancers, as assessed by whole genome sequencing, frequently have between 10,000 and 100,000 mutations in their entire genomes.[2] Cancers usually show tumour heterogeneity, containing multiple subclones.[3][4] They also frequently have reduced expression of DNA repair enzymes due to epigenetic methylation of DNA repair genes or altered microRNAs that control DNA repair gene expression.