FLT4 and Kaposi's sarcoma: Later, however, KS tumor cells were also found to express lymphatic endothelial cell (LEC)-specific markers such as VEGF receptor-3 (VEGFR-3/flt4) and podoplanin [11], [12], [13], [14], [15], [16], [17], [18], [19], arguing for their lymphatic origin.