GSTM1 and neoplasm: The principal findings of this study are: (1) RRx-001 localizes to RBCs likely by associating with cysteine residues on Hb, (2) RRx-001 treated RBCs preferentially localize to tumors by increasing RBC adhesion to the tumor endothelium in our experimental tumor models, likely by increasing phospholipid phosphatidylserine expression, and (3) localization of RRx-001 treated RBCs affects tumor viability.