SOX2 and neoplasm: To assess whether the finely tuned balance between NOTCH and SOX2 shaping tumor cell plasticity that we observed in vitro also occurs in vivo and potentially limits tumor growth control by GSI, two GSI-sensitive (HCC1599 and MB157) and two GSI-resistant (MB157R and HCC1806) GFP-luciferase expressing TNBC cell lines were engrafted into the milk duct of immune-compromised mice (Fig. 5A).