Extracellular factors are imperative to support the colonization and outgrowth of metastasizing tumour cells.39 Inflammatory cytokines or chemo-attractants have been reported to pre-determine and maintain metastasis in a variety of tumour models.40,41 In LM cells, GSEA analysis of DEGs showed that cytokine signaling, particularly TNFα-NF-κB signaling, was activated (Fig. 6a and Supplementary Fig. 9a–g), indicating that TNFα probably facilitated metastasis of LM cells. This evidence concerns the gene NFKB1 and neoplasm.