DLL4 and neoplasm: Disruption of Dll4 signalling by overexpression or inhibition of Dll4 may impair tumour angiogenesis (Noguera-Troise et al, 2006; Ridgway et al, 2006), and blockade of Dll4–Notch signalling results in an increased density of non-functional vasculature and is associated with a reduction in the growth of human xenografts (Noguera-Troise et al, 2006; Ridgway et al, 2006).