For example, in orthotopic tumor models of breast and colon cancer cells, GPR4 is activated after pH reduction and promotes tumor growth and pathological angiogenesis through p38-mediated secretion of interleukin-6 (IL-6), IL-8, and vascular endothelial growth factor-A (VEGF-A). The gene discussed is VEGFA; the disease is malignant colon neoplasm.