A drug used to treat advanced breast and endometrial cancer. It is also used to treat anorexia (loss of appetite) and cachexia (weakness and loss of body weight and muscle mass) in patients with AIDS. It is also being studied in the treatment of anorexia and cachexia in patients with cancer or other conditions. Megestrol acetate blocks the effects of the hormone estrogen in the body, which may help keep some cancer cells from growing. It may also improve appetite. Megestrol acetate is a type of progestin. Also called Megace.