Accumulating studies propose RBBP8, known to encode the endonuclease CtIP [23], as a novel susceptibility gene [24] whose functional loss increases sensitivity towards PARP1 inhibition [25, 26] similar to BRCA1 inactivation as, for instance, recently demonstrated in a mice xenograft model of breast cancer [27]. The gene discussed is RBBP8; the disease is breast cancer.