NFKB1 and post-transplant lymphoproliferative disease: A study comprising 6 monomorphic PTLD of which 5 were EBV-positive demonstrated upregulation of NFKB, PI3K, Akt, mTOR, MAPK and PKC pathways, cell cycle regulation, endoplasmic reticulum homeostasis (HSP90), and apoptosis-related proteins (caspase 7-8 and MAP2K4).