To investigate the diagnostic significance of Interleukin 12 (IL-12) in breast cancer (BC) and its correlation with other tumor markers including cancer antigen 15-3 (CA 15-3), carcinoembryonic antigen (CEA), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinases-1 (TIMP-1), and MMP9/TIMP1 ratio. The gene discussed is MMP9; the disease is breast cancer.