Do not say ever never more: the ins and outs of antiangiogenic therapies.

Angiogenesis has been described as one of the hallmarks of cancer, playing an essential role in tumor growth, invasion, and metastasis. Antiangiogenic therapy was initially perceived as a "magic bullet" that could eventually be used for the treatment of any type of cancer. For this reason inhibition of angiogenesis has become a major challenge in the development of new anticancer agents, with a countless number of antiangiogenic strategies being tested in preclinical and clinical trials. The initial pessimism about the usefulness of the antiangiogenic therapeutic approach for cancer, derived from the poor results obtained in clinical trials, turned into euphoria after the approvals of the anti-VEGF monoclonal antibody bevacizumab and the multitargeted tyrosine kinase inhibitors sunitinib, sorafenib and pazopanib. Nowadays the clinical development of antiangiogenic therapies seems to be unstoppable, not only for cancer, but also for an increasing number of non-neoplasic angiogenesis-related diseases. Nevertheless, careful analysis of the clinical results reveals that therapy with angiogenesis inhibitors often does not prolong survival of cancer patients for more than months. This fact, combined with the high prices of the new antiangiogenic therapies have made a number of oncologists to doubt if they offer "good value". Moreover, recent experimental findings suggest that some antiangiogenic drugs could promote tumor invasiveness and metastasis. The success in the discovery and pharmacological development of future generations of angiogenesis inhibitors will benefit from further advances in the understanding of the mechanisms involved in human angiogenesis.