4% and 62.9%, respectively. There was no significant difference in t-VEGF-A expression status. The five-year DFS rates of s-VEGF-A-positive and -negative cases were 73.8% and 39.9%, respectively. technical support s-VEGF-A-positive cases had significantly better survival than s-VEGF-A-negative cases (P = 0.0005). Splice variant analysis revealed that t-VEGF-A was mainly composed of VEGF165 and that s-VEGF-A included both VEGF165 and VEGF165b. In cases with no venous invasion (v0), the level of VEGF165b mRNA was significantly higher (v0 204.5 �� 122.7, v1 32.5 �� 36.7, v2 2.1 �� 1.7, P = 0.03). The microvessel density tended to be lower in cases with higher VEGF165b mRNA levels. CONCLUSION: s-VEGF-A appears be a good prognostic factor for colorectal cancer and includes VEGF165 and VEGF165b.

Keywords: Colorectal cancer, Vascular endothelial growth factor-A, Vascular endothelial growth factor 165, Microvascular density, Stromal cell INTRODUCTION The growth and metastasis of cancer depend on angiogenesis, and vascular endothelial growth factor (VEGF)-A. VEGF-A is known to be one of the most important angiogenic factors. VEGF-A protein was discovered by Ferrara in 1989 as a specific growth factor and a blood vascular permeability factor for endothelial cells[1-2]. As a result of alternative splicing, 6 VEGF isoforms of 121, 145, 165, 183, 189 and 206 amino acids are produced from a single gene[3-7]. Most studies suggest that VEGF165 is the most abundant and biologically active isoform[3,8]. The biological effects of VEGF165 are mediated by tyrosine kinase receptors, i.e.

, VEGF receptor (VEGFR) 1 (Flt-1), VEGFR2 (KDR/Flk-1), and VEGFR3 (Flt-4)[9-11]. In colorectal cancer, VEGF-A is highly expressed in the case of hematogenous metastasis; therefore, VEGF-A is assumed to have value as a prognostic factor. VEGF-A and its receptor system are deeply involved in tumor angiogenesis. Thus, they are important molecular targets in the therapeutic strategy against colorectal cancer. It has been reported that the combined chemotherapy and an anti-VEGF antibody improves the response ratio of the tumor and extends the length of survival[12-15]. Tumor cells are the predominant source of VEGF; however, stromal cells surrounding the tumor have also been shown to produce VEGF[16]. Researches on the invasive and metastatic mechanisms mainly focused on the characteristics of the cancer cell itself, and there are few reports concerning the stromal cells[17-19].

Over the past decade, the role of stromal cells has gradually become a matter of interest to many researchers. The median survival in stromal VEGF-A-positive patients was 9.7 years vs 4.3 years in stromal VEGF-A-negative patients with stage II and III colorectal cancers[20]. However, the reason why VEGF-A expression in stromal cells resulted in a better prognosis has not been clarified. VEGF165b was recently isolated from kidney epithelial cells as AV-951 an angiogenesis inhibitor[21].