Several signaling pathways participate in breast cancer resistance to radiation therapy, such as Ras/phosphoinositide 3-kinase (PI3K)/PTEN/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) (Figure 2B) (25), and Ras/Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) (MAPK) (Figure 2B) (26, 27). Here, PTEN is linked to breast cancer.