**1. Introduction**

Angiogenesis is a process that is important to the growth of cancers. It refers to when new blood vessels sprout from existing ones. This multi-step process is imperative to the physiological maintenance of the body such as tissue repair [1]. It is also thought to be a critical process that tumours depend on for the delivery of oxygen and nutrients, in order to facilitate growth and progression [2]. Both pro-angiogenic factors and anti-angiogenic factors play a role in modulating tumour neovascularisation. Notably, vascular endothelial growth factors (VEGF) and catecholaminergic signalling pathways have been shown to be key factors in angiogenesis, invasion and metastases [3]. Investigations into catecholaminergic signalling from the sympathetic nervous system have shown to increase VEGF and matrix metalloprotease (MMP) levels, promoting tumour growth, invasion and metastasis [4]. Since tumour angiogenesis requires the up-regulation of these factors, anti-angiogenic agents have now been developed. A multitude of trials have investigated the effect of anti-angiogenic agents on the progression of cancer as well as combination therapies to improve the current standard of care. However, not all patients respond to these, leading to studies that aim at elucidating the mechanisms of resistance.
