Based on the concept of a preexisting mechanism, several tumor cell lines were found to be intrinsically resistant to PARP inhibitor treatment involving BRCA-wild-type TOV112D, ES2, SKOV-3, and OV-90 cells, which was identified via elevated half-maximal inhibitory values (IC50) of olaparib [105, 148]. The gene discussed is PARP1; the disease is neoplasm.