Our results showed that 1) ERβ modulates a number of genes involved in DNA recombination and repair, 2) ERβ sensitizes GBM cells to chemotherapy drugs, 3) ERβ- KO attenuates chemotherapy induced apoptosis and cell cycle arrest genes, 4) ERβ attenuates HR repair by modulation of ATM signaling and 5) using a xenograft model, provided evidence in vivo that ERβ sensitizes GBM to chemotherapy. This evidence concerns the gene ESR2 and glioblastoma.