AKT1 and breast cancer: However, other signaling pathways have also been activated by exosomes, such as gastric cancer cell-derived exosomes, which promote tumor cell proliferation through the PI3K (phosphoinositide 3-kinase)/Akt (protein kinase B) and MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) signaling pathways, and exosomes released from stromal cells that activate the Notch3 signaling pathways in breast cancer cells [75,76].