Immunohistochemistry (IHC) analysis was performed as previously reported.20 (link) In brief, paraffin-embedded sections were baked at 60 °C for 2 h followed by being deparaffinized in xylenes for 20 min and rehydrated in an ethanol gradient. The sections were submerged into EDTA buffer and boiled for 2 mins with high-pressure for antigenic retrieval. After natural cooling, the slides were treated with 3% H2O2 to quench endogenous peroxidase activity, followed by incubation with 1% bovine serum albumin (BSA) to block non-specific binding. The slides were incubated with the MMP-2 rabbit polyclonal antibody (catalog ab110186, dilution 1:500; AbCam) overnight at 4 °C. PBS buffer was used as negative controls, and colon cancer tissue was used as positive control. After PBS washing, the sections were reacted with the biotinylated secondary antibody (Zymed, San Francisco, CA). Sections were then visualized with 3,3′-diaminobenzidine (DAB) for 2 min, counterstained with hematoxylin and were mounted under a light microscopy. Pan-cytokeratin was used to distinguish neoplastic spindle cells from fibroblast cells or other stromal cells in NPC tissues.