NFE2L2 and cancer: Elevated Nrf2 levels have been observed in head and neck [19], gall bladder [20] and lung cancer [21], and evidence indicates that a dysregulated Nrf2/Keap1 system may protect against the deleterious effects of oxidative stress, whilst also conferring properties of enhanced cellular proliferation and a drug-resistant phenotype, in certain cancers [20,22,23], effectively acting as a double-edged sword [22].