A type of cancer that begins in germ cells (cells that form sperm or eggs). Dysgerminomas occur most often in the ovaries, but they may also occur in other areas of the body, including the central nervous system. Some dysgerminomas make a hormone called beta-human chorionic gonadotropin (beta-HCG) that may cause signs and symptoms of disease. Dysgerminomas tend to grow and spread slowly. They are the most common type of ovarian germ cell tumor. They usually occur in teenage girls or young women.