The present invention provides a method for determining the RES phenotype in a tumor. The present invention further provides a method for predicting the sensitivity of a tumor to an epigenetic treatment, the method comprising determining the RES phenotype in said tumor, the presence of the RES phenotype in a tumor being indicative of a tumor sensitive to an epigenetic therapy. The present invention also provides a method for diagnosing an aggressive tumor and for selecting a patient affected with a tumor for an epigenetic therapy.
