BDNF and pancreatic adenocarcinoma: BDNF expression was significantly correlated with CCL2-CCR2 (CCL2, r = 0.35, p < 0.01; CCR2, r = 0.28, p < 0.01, Figure 5(b)) signaling axis in PAAD, which has been proven to be associated with Th2 polarization and infiltration [34].