NFE2L2 and cancer: SFN: sulforaphane; CSC: cancer stem cell; NF-κB: nuclear factor kappa B; HER2: human epidermal growth factor receptor 2; TNBC: triple-negative breast cancer; ALDH+: aldehyde dehydrogenase-positive; LSD1: lysine-specific demethylase 1; HDAC5: histone deacetylase 5; ALDH1A1: aldehyde dehydrogenase 1A1; ROS: reactive oxygen species; Nrf2: nuclear erythroid 2-related factor 2; TGF-β1: transforming growth factor beta 1