CXCL9 and breast cancer: Next, we conducted the PPI network to construct and identify the hub genes (high confidence = 0.7), where the first 10 genes were CD8A, PTPRC, CD2, CD19, CCR7, CXCR3, LCK, CXCL9, IL7R and PRF1, which occupied an essential role in occurrence and development of BC (Additional file 1: Fig. S1G, H).