Colorectal cancer is the second most common cause of cancer deaths in New Zealand and among the highest worldwide. Approximately 50% of patients have metastases at diagnosis or follow-up. Our aim is to investigate those genes that may aid early diagnosis and accurate prognosis of colorectal cancer. In this study we have focused on the angiopoietin/Tie2 pathway that has been shown to play an important role in blood vessel homeostasis and remodeling. Using semi-quantitative relative RT-PCR we have measured gene expression of Angiopoietin-1 (Ang-1), Ang-2, and Tie2 in samples taken from patients with pre-malignant adenomas (n = 9), primary adenocarcinomas (Dukes stage A-D, n = 31), and in patient-matched adjacent histologically normal colon tissue. We observed significant increases in Ang-2 mRNA levels in both Dukes stage A (p = 0.027) and C (p = 0.007) tumors compared to matched histologically normal tissue. No significant differences were observed in Ang1, Ang2, or Tie2 gene expression among adenomas and Duke’s stage A-D adenocarcinomas. Analysis showed that Ang-1 mRNA levels were negatively correlated with patient age (r = -0.355, p = 0.025), and were significantly lower in adenocarcinomas with no lymphocytic response, regardless of Duke’s stage (p = 0.05). There were no correlations between Ang1, Ang2 and Tie2 with tumor grade, tumor size, lymph node status, gender and vascular invasion (p>0.05). Using immunohistochemistry, we have double-stained high and low Ang-1 expressing human colorectal tumors using anti-CD1 and anti-alpha-smooth muscle actin antibodies to determine pericyte coverage, an indicator of vessel maturity. Multivariate survival analysis, taking into account tumor stage, patient age and vascular invasion showed significant associations between Ang1 (p = 0.007) and Tie2 (p = 0.041) and survival. In both cases, higher levels of Ang1 and Tie2 gene expression were associated with longer survival (median follow-up time 4.8 years, range 0.4-6.4 years). The angiopoietin/Tie2 pathway has a major role in both inflammatory and angiogenic processes. The association we observed between increased Ang1 expression in colorectal tumors and longer patient survival supports the concept that Ang1 slows tumor progression. Our results also indicate that lymphocytic response may play a role in determining Ang1 levels in colorectal adenocarcinomas.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]