IL1B and neoplasm: To identify the secretory factor(s) which stimulated JAG1 expression in the CM of brain metastatic cells, we performed a cytokine antibody array analysis and found that IL-1β, which is known to promote tumour growth, angiogenesis and invasion, was the most significantly enriched cytokine in the CM of 231BrM cells (Fig 2A; Supporting Information Fig S2A).