The short form of the alternatively spliced flt-4 but not its ligand vascular endothelial growth factor C is related to lymph node metastasis in human breast cancers

Angiogenesis is essential for tumor growth and metastasis, It is regulated by numerous angiogenic factors, one of the most important being vascular en dothelial growth factor (VEGF), Recently, VEGF-C, a new VEGF family member, has been identified that binds to the tyrosine kinase receptors flt-4 [VEG F receptor (VEGFR) 3] and KDR (VEGFR2), Although the importance of VEGF has been shown in many human tumor types, the contribution of VEGF-C and its p rimary receptor flt-4 to tumor progression is less well understood. We have therefore measured the level of VEGF-C, flt-4, and KDR mRNA by RNase prote ction assay and the pattern of VEGF-C expression by immunohistochemistry in 11 normal breast tissue samples and 61 invasive breast cancers, No signifi cant difference in VEGF-C expression was observed between normal and neopla stic breast tissues (P = 0.11), There was a significant correlation between VEGF-C and both flt-4 (P = 0.02) and KDR (P = 0.0002), but no association was seen between VEGF-C and either lymph node status (P = 0.66) or number o f involved nodes (P = 0.88, patient age (P = 0.83), tumor size (P = 0.20), estrogen receptor status (P = 0.67), or tumor grade (P = 0.35), No signific ant relationship was present between VEGF-C and vascular invasion (P = 0.30 ), tumor vascularity (P = 0.21), VEGF-A (P = 0.62), or thymidine phosphoryl ase expression (P = 1.00), VEGF-C was expressed pre-dominantly in the cytop lasm of tumor cells, although occasional stromal components including fibro blasts were also positive. We could demonstrate no association between lymp h node metastasis and either VEGF-C (P = 0.60 or flt-4 (P = 0.4), However, we did observe a significant loss of the long but not the short isoform of flt-4 in tumors compared with normal tissues (P = 0.02 and P = 0.25, respec tively), and this difference was largely accounted for by the reduction of long flt-4 in node-positive tumors. These findings strongly support a role for VEGF-C/flt-4 signaling in tumor growth by enhancement of angiogenesis a nd/or lymphangiogenesis and suggest that differential regulation of these p rocesses may be controlled via flt-4 Isoform transcription. They further su ggest that the measurement of flt-4 isoform expression may identify a patie nt group that is likely to have node-positive disease and therefore benefit from additional treatment and also emphasize an additional ligand interact ion that could be exploited by anti-VEGFR therapy.