Mitoxantrone is a chemotherapy drug that targets fast dividing cells, such as cancer cells and kills them. It decreases the number of symptoms and delays disability development in multiple sclerosis. It relieves the pain in those with advanced prostate cancer and serves as a treatment for some types of leukemia. As a member of the anthracenediones group, mitoxantrone treats MS by stopping the immune system cells from reaching the spinal cord and the brain to cause damage. For cancer, it stops the growth and spread of cancer cells.