One of such promising examples is represented by tumors with deficient homologous recombination due to the mutations in BRCA1 or BRCA2. These tumors show a high sensitivity to poly(ADP-ribose)polymerase inhibitors that block alternative DNA repair pathways and may help to kill BRCA1-deficient cancer cells (recently reviewed in [9,10,11]). The gene discussed is BRCA1; the disease is cancer.