Quantitative analysis of lymphangiogenic markers in human colorectal cancer

Lymphatic spread of colorectal cancer cells to regional lymph nodes is one of the early events in metastatic cancer, and is often associated with distant metastatic spread and a poor prognosis. This study examined lymphangiogenic factors, and in particular a panel of newly discovered lymphangiogenic markers, in colorectal cancer tissues from a cohort of patients. Paired samples (background normal mucosa and cancer) of colon tissue were obtained from patients with colorectal cancer. The expression and levels of the VEGF-C and VEGF-D cytokines, the VEGF receptors VEGFR-2 and VEGFR-3, and newly described lymphatic endothelial markers, LYVE-1, Prox-1, podoplanin and 5'-nucleotidase were assessed. RNA was extracted from the frozen colon tissues. The level of expression for each factor/marker was determined using RT-PCR and quantified using a real-time quantitative PCR (RT-QPCR) technique, with respective cloned cDNA plasmids as internal standards. VEGF-D was expressed to a significantly higher degree in the colon tumour tissues. There was no significant difference between the expression levels for both VEGF-C and its receptor, VEGFR-2, in background and cancer tissues. However, levels of the VEGFR-3 receptor were found to be significantly higher in colon cancer than the normal background tissues. LYVE-1 levels were below detection in most cases. There was a significant increase in the degree of Prox-1 and 5'-nucleotidase expression in colon cancer tissue. Podoplanin expression was also increased in the cancer samples. These markers indicate an increase in lymphangiogenesis in colon cancer, and may therefore have prognostic value for colon cancer patients.