A drug used with other drugs to treat acute myeloid leukemia (AML) and advanced prostate cancer that did not get better with hormone therapy. It is also used to treat certain forms of multiple sclerosis (MS). It is also being studied in the treatment of other types of cancer. Mitoxantrone hydrochloride damages the cell’s DNA and may kill cancer cells. It may also stop certain immune cells from causing damage to the brain and spinal cord. Mitoxantrone hydrochloride is a type of antitumor antibiotic.