e15111 Background: Neuropilin (NRP) was initially described as non-tyrosine kinase receptors for neuron guidance factor belonging to the Semaphorin family. Two subtypes, NRP-1 and NRP-2 have been isolated. Neuropilins are widely expressed not only normal developing tissues but also several types of tumor cells. It was reported that the expression of NRP-1 is increased by VEGF, mediated through VEGFR-2, which correlates with tumor growth and invasiveness in colorectal cancer. NRP-2 knockout mice studies showed marked deficits in the development of small lymphatic vessels and its function was associated with the formation of lymphatic network, but the role of NRP-2 in colorectal cancer remains unknown. METHODS We have newly established two useful anti- Neuropilin antibodies against CUB domains of NRP-1 and cytoplasmic domains of NRP-2. In recent study, we have analyzed the expression of NRP-1 and NRP-2 in some cultured cell lines by western blot and the clinicopathological significance in colorectal cancer. Tissues samples were obtained from 72 primary colorectal adenocarcinomas (colon:39 cases, rectum:33 cases). The pathologic stage were as follows; stageI:10 patients, II:25 patients, III:26 patients and IV:11 patients. NRP-1 and NRP-2 gene expression was evaluated by RT- PCR, which was compared with immunohistochemical examination of colorectal cancer tissues. Constitutive expression of NRP-1 was detected in PC3, HT29, PC9 and PC13 cell lines and NRP-2 in HT29, PC3 and PC9. RESULTS There was significant correlation between NRP-1 and -2 protein expression and both of mRNA expression. The expression of NRP-1 showed apparent correlation with liver metastasis (p=0.027) and venous invasion (p=0.0025), while NRP-2 expression was correlated with lymph node metastasis (0.001) and lymphatic invasion (0.039) by immunohistochemical analysis. The post-surgical treatment observation revealed that patients with co- expression of NRP-1 and NRP-2 were significantly correlated with poorer prognosis than both NRP-1 and NRP-2 negative patients (p=0.035). CONCLUSIONS These results suggest that NRP-1 acts as angiogenesis factor and NRP-2 acts lymphangiogenesis factor, both of them are useful predictive marker in colorectal cancer. No significant financial relationships to disclose.