NAD(P)H:quinone oxidoreductase 1 (NQO1) is a flavoprotein that catalyzes the two-electron reduction of quinones and their derivatives. This enzyme protects cells against redox cycling and oxidative stress. The expression of NQO1 is increased in liver, colon and breast tumors and non-small cell lung cancer (NSCLC) compared with the normal tissues. Moreover, expression levels are also elevated in developing tumors, suggesting a role for NQ01 in the prevention of tumor development. Studies on NQO1 knockout mice suggest that the lack of NQO1 enzymatic activity changes intracellular redox states resulting in a reduction in apoptosis, which in turns leads to myeloid hyperplasia of bone marrow.