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PARP inhibitors seemed down for the count in 2011, after Sanofi’s iniparib failed in a phase III trial in triple-negative breast cancer and AstraZeneca’s olaparib suffered a setback in ovarian cancer. But as drug developers realized that iniparib was not a true PARP inhibitor, and adopted a more cautious clinical trial strategy, the class mounted a comeback. In the past 5 years the FDA has approved four PARP inhibitors, from AstraZeneca, Clovis, GlaxoSmithKline and Pfizer, most notably for ovarian and breast cancers in patients with BRCA mutations.