In two PDX cases (PDX1 and PDX9), miR-509-3 could significantly increase the sensitivity to Olaparib along with the decrease of RAD51 positive rate (mean tumor weight NC + Olaparib vs. miR-509 + Olaparib; PDX1 P < 0.05, PDX9 P < 0.05). The gene discussed is RAD51; the disease is neoplasm.