Just as the other oncogene we mentioned above, such as HER2, BRAF, when ROS1 is activated by its ligands, downstream signaling pathways such as the PI3K/AKT/mTOR, JAK/STAT, and MAPK/ERK signaling pathways are also activated, leading to the proliferation of lung cancer cells and tumor invasion (31). The gene discussed is PIK3CA; the disease is lung cancer.