PTEN and melanoma: Moon et al. found that quiescent melanocyte SCs (MCSCs) in the HF bulge were refractory to BrafV600E-driven tumorigenesis and depletion of phosphatase and tensin homolog (Pten; Box 1), whereas melanomas arose within the same genetic background following MCSC activation by ultraviolet (UVB) radiation or drug-induced inflammation (Moon et al., 2017).