Although PARP inhibitors are mainly used in BRCA + tumors, recent studies also suggest high responses in non-BRCA mutated cells, including genes like ATM, ATR, RAD51, and BARD1 that are related to genomic instability generation and indicative of homologous recombination deficiency (HRD). This evidence concerns the gene RAD51 and hypoparathyroidism-retardation-dysmorphism syndrome.