SPON1 and cancer: Some of these genes such as Vascular Endothelial Growth Factor (VEGF), Vascular Endothelial Growth Factor Receptor 1 (VEGFR1), Spondin 1 (Spon1), Transforming Growth Factor beta (TGFβ) or Metalloproteinase 9 (MMP9) were exclusively upregulated in cancer cells from the peritoneal cavity (Figure 4C).