Despite its clinical activity, most promisingly in trastuzumab-refractory ErbB2-positive breast cancer [10], 17-AAG suffers from a limited aqueous solubility, low oral bioavailability [10], [11], susceptibility to the metabolic activities of polymorphic enzymes (CYP3A4 and NQO1/DT-diaphorase [5], [12], [13]), and hepatotoxicity [7], [8], [9]. Here, NQO1 is linked to breast cancer.