PGF and colorectal cancer: Indeed, it has been reported that VEGF expression is higher in colorectal cancer metastases than in the primary tumor.23 Moreover, colorectal cancer cell lines isolated from primary tumor were characterized by a higher expression of multiple proangiogenic factors, such as placental growth factor, thrombopoietin, and transforming growth factor β1, compared to tumor cell lines isolated from metastases.14 Taken together, these data are consistent with a more complex tumor microenvironment angiogenic network in the primary tumor than in the metastases.