We read with interest the recent article by Vleugel et al, in which the presence of lymph vessels was investigated during breast cancer progression.¹ The authors claim that the observed absence of intratumorous lymph vessels in invasive breast cancer can be explained by the absence of lymphangiogenesis. In our opinion, this is a rather bold conclusion because only lymph vessel density was assessed and not lymph endothelial cell proliferation. By analogy with angiogenesis, the mere presence of a number of vessels at a certain time point—for example, at surgery—provides no information concerning the degree of ongoing angiogenesis.² Lymph vessel density is the net result of lymphangiogenesis …