Abstract: The invention provides TRF1 inhibitors and compositions comprising them for the treatment of a brain cancer, such as a glioblastoma, and particularly a glioblastoma multiforme (GBM). PI3K inhibitors can be among the TRF1 inhibitors used. The compositions can comprise more than one TRF1 inhibitor, being particularly advantageous that at least one of the inhibitors is a PI3K inhibitor and that at least a second possible TRF1 inhibitor present is selected from the group an RTK inhibitor, a MEK inhibitor, an ERK inhibitor, an HSP90 inhibitor, docetaxel and gemcitabine, because such compositions show a synergic effect. The invention also relates to a method for identifying compounds candidates to be used for treating glioblastoma or other cancers, which method is based on the identification of the compound as a TRF1 inhibitor.