Olaparib and other PARP inhibitors (PARPis) are especially cytotoxic to BRCA1/2-mutated, homologous recombination (HR) DNA repair deficient, tumor cells by blocking PARP-mediated DNA repair and promoting DNA replication stress through trapped PARP-DNA complexes leading to chromosomal instability, cell cycle arrest and ultimately apoptosis [2,3,4]. The gene discussed is PARP1; the disease is neoplasm.