Drugs that block a cell repair enzyme known as PARP show promise at treating the most aggressive forms of breast cancer, some new studies suggest. In one trial, researchers found that a PARP-inhibitor improved survival by 60 percent in women who had triple-negative breast cancer, when compared to patients who had chemo alone. Another study found that a PARP-inhibitor called olaparib shrunk tumors in one third of patients. Experts say the drug class works by preventing cancer cells from...