PARP inhibitors are a type of targeted therapy commonly used to treat breast cancer and ovarian cancer, among others. They target PARP, or poly (ADP-ribose) polymerase, which is a protein in cells that helps repair damaged DNA.

DNA damage is a normal part of a cell’s life cycle, and it doesn’t prevent cells from growing and dividing, as long as they can repair the damage. “PARP inhibitors are a class of drug that interferes with...