PAX3 and breast cancer: The role of BC cells at motor exit points was investigated using three different types of manipulations/model systems: (1) surgical ablation of neural crest cells in chick embryos; (2) Splotch (Pax3 mutant) mice embryos whose neural crest cells fail to delaminate from the trunk region of the neural tube [38–40]; (3) the selective ablation of Krox-20-expressing BC cells by targeting diphtheria toxin to the Krox20 locus [29].