DDR2 and ovarian cancer: Activation of the PI3K/AKT/mTOR/HIF-1α axis promoted the expression of Twist, a transcription factor that increases discoidin domain receptor 2 (DDR2), which is activated by collagen I (102), and then upregulates the expression of membrane type 1-matrix metallopeptidase 14 (MT1-MMP) and LOX, which is an essential factor in the invasion of ovarian cancer (103, 104) (Figure 3).