CD34 and breast cancer: Of note, this behavior is very close to what we observed by CD34 immunostaining on human urinary bladder and breast cancer tissues, indicating that our vessel wall−MCTS confrontation model is suitable for analyzing the contribution of vessel wall-derived VW-SPCs to tumor vascularization at a more differential level, as it was possible, yet, e.g., separating the role of mature endothelial cells from the vascular wall progenitors.