NFE2L2 and skin neoplasm: Topical application of sulforaphane prior to the chemical treatments decreased the incidence of skin tumor compared with the control group in the wild type mice, and such chemoprotective effect of sulforaphane was not seen in the Nrf2(-/-) knockout mice, implicating that that Nrf2(-/-) knockout mice are more susceptible to chemically induced skin tumorigenesis and that Nrf2 is involved in the chemoprevention by sulforaphane.