Decrease in Ki-67 during window-of-opportunity studies is an indication of anticancer activity of the drug being studied.25-28 The Valproic Acid Signature Trial (VAST) was a window-of-opportunity study designed to assess the tolerability of VPA, to validate the ability of the GDSS-VPA to predict decreases in Ki-67 and tumor changes on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) scanning, and to correlate VPA biologic activity with blood VPA levels and histone acetylation changes in blood. This evidence concerns the gene MKI67 and neoplasm.