L. J. Fernandez1, A. L. Olex2, A. R. Wolen2, D. A. Fenstermacher2, M. G. Dozmorov2, K. Takabe1,3 1Virginia Commonwealth University,Department Of Surgery, Division Of Surgical Oncology,Richmond, VA, USA 2Virginia Commonwealth University,Department Of Biostatistics,Richmond, VA, USA 3Virginia Commonwealth University,Department Of Biochemistry & Molecular Biology,Richmond, VA, USA
Introduction: Angiogenesis is known to be a critical factor in progression of many cancers including colorectal cancer. Bevacizumab, an antibody against VEGFA (a well known mediator of angiogenesis) is used for the treatment of colorectal cancer, mostly in the advanced and recurrent setting. To date, there is no objective data that demonstrate a relationship between angiogenetic factors and survival. Using The Cancer Genome Atlas (TCGA) database, we sought to determine if the level of expression of angiogenesis-related genes in colorectal adenocarcinoma (COAD) tumors is associated with survival.
Methods: All available clinical and RNA-seq data from COAD samples were obtained from the TCGA database. RNA-seqV2 data for VEGFA, VEGFR1, VEGFR2 (markers of angiogenesis) and CD31 (marker for vascular endothelial cells) was normalized for analysis using R; Gene-expression was compared between normal and tumor samples for our genes of interest. A cutoff was identified for each gene of interest to categorize each sample as either low or high. All the available clinical data in the database was analyzed by hand to maximize the number of patients with disease free (DFS) and overall survival (OS) data points. Kaplan-Meier curves were used to plot DFS and OS and statistical significance was calculated. Only the gene-expression in the tumor was used for survival analysis.
Results: There were 314 COAD samples with RNA-seq data; 41 corresponded to normal tissue and 273 to tumor samples. Of the 273 patients with tumor RNA-seq, 240 patients also had usable OS data available and 233 had usable DFS data available. There was a significant difference in expression of VEGFA (p=1.352e-04), VEGFR1 (p=7.613e-04) and CD31 (4.713e-09) between colon cancer and normal colon. VEGFA and VEGFR1 were highly expressed in tumors versus normal tissue, implying higher angiogenesis, while CD31 was higher in normal tissue. These expression differences are in agreement with the notion that normal colon mucosa is more vascular than the tumor, and tumors have higher angiogenetic activity. When comparing tumors based on their gene expression we found that there was worse DFS in patients with tumors that express higher levels of VEGFA (p=0.00498), VEGFR1 (p=0.002), VEGFR2 (p=0.03411), and CD31 (p=0.03619). Also, there was worse OS for patients with higher expression of VEGFA (p=0.00502). Our results are in agreement with the notion that tumors that express high levels of pro-angiogenic factors and receptors, as well as generation of vessels are associated with poor survival.
Conclusion: Tumors with increased angiogenesis, represented by high expression of VEGFA and VEGF receptors, have worse disease-free and overall survival. This is in agreement with the improved survival that was been seen in patients with metastatic colorectal cancer when treated with Bevacizumab.