PARP1 and cancer: Patients with the hereditary breast and ovarian cancer syndrome (HBOCS) commonly have mutations in the key genome stability proteins, BRCA1 and BRCA2. Research over the last decade has yielded a promising therapeutic strategy for BRCA mutant cancers, through the observation that cells mutant for the BRCA genes are exquisitely sensitive to inhibition of the nuclear enzyme poly-adenosine ribose polymerase (PARP), through a synthetic lethal mechanism.