POU3F2 and neoplasm: The phenotype-switching model of tumour progression dictates that these two mutually exclusive populations are able to selectively switch back and forth to drive tumour growth through a predominately proliferative cellular phenotype driven by MITF, and tumour metastasis by an invasive BRN2 directed cellular population (Hoek et al., 2008, Hoek and Goding, 2010).