Stromal cells in the tumour microenvironment secrete CXCL12, which in turn binds to the CXCR4 receptor on the cancer cell and activates many signalling pathways (e.g., PI3K/AKT and MAPK) that promote tumour cell proliferation, tumour cell migration, the EMT, and even metastasis (Figure 3) [57]. The gene discussed is PIK3CA; the disease is cancer.