Immunohistochemistry (IHC)

MET IHC evaluation was performed using Confirm anti-Total c-MET (SP44) rabbit monoclonal antibody (Ventana Medical Systems, USA). IHC was carried out on the VENTANA Benchmark XT stainer using Ultraview detection system according to the manufacturer's instruction. The expression level of MET protein was recorded with the H-score assessment combining staining intensity (0–3) and the percentage of positive cells (0–100%) [29]. There were four staining scores as follows: 3+ (≥50% of tumor cells staining with strong intensity); 2+ (≥50% of tumor cells with moderate or higher staining but <50% of tumor cells with strong intensity); 1+ (≥50% of tumor cells with weak or higher staining but <50% of tumor cells with moderate or higher intensity); 0+ (no staining or <50% of tumor cells with any staining intensity). Score 2+ and score 3+ were defined as positive MET IHC or MET protein overexpression. Otherwise, a tumor was defined as negative MET IHC. IHC findings were analyzed by two independent investigators.