In addition, sympathetic nervous system activation can indirectly lead to the release of several protumour factors, including matrix metalloproteinase-9 (MMP-9), VEGF, TGF-β, IL-6 and IL-8, triggering a series of inflammatory responses to stimulate tumour recurrence and metastasis (48, 56). This evidence concerns the gene TGFB1 and neoplasm.