Nrf2 overexpression secondary to Keap1 dysfunction, on the one hand, protects the normal cells from carcinogenic reactive substances, but on the other hand, promotes cancer by protecting the cells from anticancer drugs, especially those acting by generating fatal oxidative molecules; thus, the Keap1–Nrf2 pathway acts as a “double-edged sword” (51). The gene discussed is KEAP1; the disease is cancer.