Molecular model of the chemotherapy drug olaparib. This drug targets the DNA (deoxyribonucleic acid) repair enzyme PARP-1 (poly (ADP-ribose) polymerase). Cancers caused by mutations in the BRCA1 or 2 genes, which include some ovarian, breast and prostate cancers, rely heavily on this enzyme to repair their DNA. If a cell's DNA cannot be repaired, the cell dies. Atoms are represented as spheres and are colour-coded: carbon (light blue), hydrogen (white), nitrogen (dark blue), oxygen (red) and fluorine (green).