PDPN and breast cancer: Although our results support that the newly generated PDPN-tk transgenic mice enable the specific targeting of LECs in various models of lymphangiogenesis, including tumor lymphangiogenesis, it remains possible that immunolabeling for PDPN could be observed in other stromal cells in the tumor microenvironment, including cancer-associated fibroblasts, as noted in human breast cancer tissues [41–43].