Angiogenesis and cancer: A cross-talk between basic science and clinical trials (the "do ut des" paradigm).

Angiogenesis plays a crucial role in facilitating tumor growth and the metastatic process, and it is the result of a dynamic balance between pro-angiogenic factors, like vascular endothelial growth factor (VEGF) and platelet-derived growth factor, and antiangiogenic factors, like thrombospondin-1 and angiostatin. Many drugs that target human tumors, like bevacizumab and some VEGF-receptor tyrosine-kinase inhibitors (e.g., BAY 43-9006, SU11248 and PTK787/ZK222584) have been studied in clinical trials, with favorable toxicity reports and encouraging results in advanced colorectal cancer, renal cell cancer, breast cancer and non-squamous non-small cell lung cancer, either combined with chemotherapy, or in monotherapy. Another potential approach to inhibiting angiogenesis is through metronomic chemotherapy (low doses of chemotherapy for long periods of time). This review describes the mechanisms of the angiogenic process and evaluates the recent data about antiangiogenic therapies in clinical trials.