Methylseleninic acid (MSA) is a small-molecule activator of FOXO1 that had been shown to activate FOXO1 in prostate cancer cells and to increase FOXO1 expression in Ewing sarcoma cells paralleled by a significant decrease in ES tumor growth.33, 34 To test if FOXO1 could be a valid therapeutic target in OS, we explored the effects of MSA on OS cells. This evidence concerns the gene FOXO1 and Familial prostate cancer.