As we found endogenous FOXO1 to be negatively regulated by EWS-FLI1 at transcriptional and post-translational levels in ES, a chemical compound, methylseleninic acid (MSA), previously shown to reactivate FOXO1 in prostate cancer cells,21 was investigated in a proof of principle study for its potential to reactivate FOXO1 activity in ES cells. This evidence concerns the gene EWSR1 and prostate cancer.