IL6 and neoplasm: Our findings that vascular permeability is induced via secretion of IL-6 from IMs, and that blocking IL-6 results in a notable reduction in both vascular leakiness and metastasis in vivo, not only support established in vitro findings but also suggest a mechanistic basis for how tumour EVPs can prime and exploit cell populations within the pre-metastatic microenvironment to facilitate metastasis.