A substance being studied in the treatment of breast, ovarian, and prostate cancers caused by mutations (changes) in the BRCA1 and BRCA2 genes. It is also being studied in the treatment of other types of cancer. It blocks an enzyme involved in many functions of the cell, including the repair of DNA damage. DNA damage may be caused by normal cell actions, UV light, some anticancer drugs, and radiation used to treat cancer. Olaparib may cause cancer cells to die. It is a type of targeted therapy agent and a type of poly (ADP-ribose) polymerase inhibitor. Also called AZD2281 and PARP inhibitor AZD2281.