CCL21 and breast cancer: Prior to the investigation of the role of CCL21/CCR7 pair in VEGF-C production, we have screened the constitutive expression of CCR7, CCL21, and VEGF-C in two well differentiated, luminal type (T47D, MCF-7) and two poorly differentiated basal type (Hs578t, MDA-MB-231) breast cancer cell lines (Additional file 1: Figure S1A and B).