The invention provides an in vitro method for determining the likelihood for a patient affected with a tumor to respond to a treatment with a pro-apoptotic peptide able to disrupt interaction between caspase 9 and PP2A, which method comprises determining expression level of at least each of VIM, MK167, TCF7L2, NEK2, BIRC5, MCL1, and PLK1 genes, in a biological sample of said patient.