One notable feature of the BRCA/PARP1 synthetic lethal effect, which contributes to its translational value, is that it is highly penetrant [17]; i.e., in otherwise molecularly diverse pre-clinical models, and cancer patients, the presence of the predictive biomarker, in this case BRCA1 or BRCA2 mutation, more often than not predicts a profound antitumour cell response to a PARP inhibitor. The gene discussed is PARP1; the disease is cancer.