A drug used to treat certain types of breast cancer that have spread to other parts of the body. It is used in patients with certain mutations (changes) in the BRCA1 or BRCA2 genes who have HER2-negative cancer. It is also used to treat recurrent ovarian epithelial, fallopian tube, or primary peritoneal cancer that has gotten better after treatment with anticancer drugs that included platinum. Olaparib is also used to treat advanced ovarian cancer. It is used in patients with certain mutations in the BRCA1 or BRCA2 genes who have already been treated with at least three other types of anticancer drugs. It is also being studied in the treatment of other types of cancer. Olaparib blocks an enzyme involved in many cell functions, including the repair of DNA damage. Blocking this enzyme may help keep cancer cells from repairing their damaged DNA, causing them to die. Olaparib is a type of poly (ADP-ribose) polymerase inhibitor. Also called AZD2281, Lynparza, and PARP inhibitor AZD2281.