STA-9090 is drug which inactivates or blocks the work of a protein called Heat Shock Protein 90 or HSP90. HSP90 is a protein that helps some molecules inside the cells have the right shape. By stopping it's activity, these molecules never get to have the right structure to be functional and they are destroyed. We believe that if we stop the activity of HSP90, the rapidly dividing cells in the tumor(s) will slow down since their proteins will not be functional without the help of HSP90.