2 sorafenib or sunitinib. The other class of compounds targets the mTOR pathway. Patients who progressed on sorafenib or sunitinib as well as patients who have a poor prognosis are treated with mTOR blockers such as temsirolimus [20, 21] or everolimus [22]. Deforolimus is also a new generation of anti-mTOR compounds for the treatment of RCC [23]. 2. Lack of Predictive Factors for the Success/Failure of Anti-Angiogenic Therapies One of the main problems for patients treated with anti- angiogenic therapies is the lack of an eﬀective predictive biomarker for their use. Many trials have tried to identify predictive biomarkers to assist in the selection of appropriate therapies. However, contradictory results from a number of these studies necessitate further investigations. Indeed, the circulating VEGF, thought to be associated with BVZ eﬃciency, is not predictive on beneﬁt as has been shown in a phase II trial on RCC [11, 24]. Plasma levels of VEGF were not predictive of response to treatment by BVZ in other cancers either [24–26]. In the same way, no correlation had been observed with circulating endothelial cells (CECs) or circulating endothelial progenitors (CEPs) at only early stage, where RCC is rare to be diagnosed [27]. In summary, identiﬁcation of predictive biomarkers for this treatment failed even though hypertension is thought to be a good candidate as a predictive marker of outcome with BVZ plus INF as the ﬁrst-line treatment in advanced RCC [15, 28] as well as sunitinib in metastatic RCC treated patients [29]. 3. Different Biological Effects Depending on Ligands and/or Receptors Involved VEGF binds to its receptors, which then form either homodimers or heterodimers. Following the dimerization, the receptors are transphosphorylated and the downstream signalling pathways are activated. Furthermore, the kinase domain of each type of receptor is not the same and consequently, signalling will diﬀer depending on the receptor involved. Thus, in the case of heterodimerization, the kinase domain of VEGFR1 will phosphorylate diﬀerent tyrosine sites than VEGFR2 for example [30]. The same observations are also found with VEGFR2, and VEGFR3 [31]. Further- more, depending on the ligand bound to the receptor, the signalling pathway can be rather diﬀerent as has been well- described previously by Autiero et al. [32]. The situation is also complicated by the fact that neuropilin-1 a co-VEGFR is overexpressed on RCC cells and induces a speciﬁc activation of the PI3 Kinase pathway [33]. Whereas VEGFR are not expressed on RCC cells, neuropilin overexpression mediates potent proliferative and invasive capacities. 4. Implication of VEGFxxxb Isoforms VEGF-A is the ﬁrst form of VEGF that was described twenty years ago for which the codiscoverer Napoleone Ferrara was awarded the Lasker Prize [34]. The pre-mRNA of VEGF-A undergoes alternative splicing leading to diﬀerent isoforms Journal of Nucleic Acids noted as VEGFxxx (xxx stands for the number of amino acids present in proteins minus the signal peptide). The major ones are VEGF165, VEGF189, and VEGF121. There are also a few minor isoforms spliced from the pre-mRNA, which are VEGF206, VEGF183, VEGF145 and VEGF148, and VEGF111 although their functions remain less clear (Figure 1) [35–40]. In 2002 Bates et al. identiﬁed a splice variant of VEGF165, VEGF165b that is expressed in most normal tissues and downregulated in cancers especially in RCC [41]. Furthermore, this ﬁnding could put a full stop to the paradox of a high level of VEGF in podocytes where angiogenesis is not upregulated. As suggested by Bates and Harper, the codiscoverers of VEGFxxxb, the existence of anti-angiogenic forms of VEGF “needs reinterpretation or at worst, require repeating the experiment with reagent that diﬀerentiate between isoforms families” [42]. In light of the discovery of Bates et al., these forms of VEGF may be anti-angiogenic forms [41, 43]. After the identiﬁcation of VEGF165b, a new sub-family of VEGFxxxb isoforms were identiﬁed (VEGF189b, VEGF121b) (Figure 1) [42]. Since then, a few publications assessed the anti- angiogenic or at least a less angiogenic outcome of VEG- Fxxxb isoforms by, in particular, the downregulation of VEGFR signalling pathway and a decrease of tumour growth [44–46]. These results have been achieved in vitro on proliferation and migration of endothelial cells along with in vivo studies on tumour volume of RCC, prostate, melanoma, and colorectal cancers and on experimental choroidal neo- vascularization [44, 47–50]. Moreover, the downregulation of VEGF165b expression leads to metastatic melanoma while VEGF165b expression prevents metastasis of malignant melanoma [51]. We can hypothesize that the ratio between the pro- and the anti-angiogenic or the less angiogenic isoforms may be crucial for the angiogenic balance. Recent results strongly suggest that VEGFxxxb may act as an anticancer therapy [45, 47, 48] and as an eﬃcient therapy of eye pathologies associated with exacerbated angiogenesis [52]. 5. VEGFxxxb Isoforms as an Explanation for the Failure of Anti-Angiogenic Treatments The identiﬁcation of VEGFxxxb isoforms has complicated the initial notion that targeting the pro-angiogenic forms of VEGF would be beneﬁcial for the treatment of diseases associated with abnormal angiogenesis. Therefore, BVZ can recognize and bind VEGFxxxb as well as VEGFxxx isoforms since BVZ recognition motif is located in VEGFR-binding domain of VEGF [53]. Hence, the concomitant presence of VEGFxxx and VEGFxxxb isoforms may contribute to the inhibition of the anti-angiogenic eﬀect of BVZ on tumour growth [45]. This hypothesis is particularly striking since we have detected VEGFxxx and VEGFxxxb isoforms in 70% of the RCC we have tested (Gre´pin, R and Page`s, G personal communication). Thus, BVZ can trap the VEGFxxxb isoforms that are, by themselves, capable of decreasing the activation of the angiogenic pathway.