S100A9 and neoplasm: We next detected neutrophil infiltration in the premetastatic niche and metastatic lung of WT and EMCNecko mice by immunofluorescence staining and found that Ly6G+ and S100A9+ (neutrophil marker) cells were significantly recruited in the lungs of EMCNecko tumor-bearing mice compared with WT tumor-bearing mice (Fig. 4G, Additional file 3: Fig. S3E).