MMP9 and hepatocellular carcinoma: Promising proteomic biomarkers such as glypican-3 (GPC3), osteopontin (OPN), midkine (MDK), dickkopf-1 (DKK-1), alpha-l-fucosidase, squamous cell carcinoma antigen-1 (SCCA-1), Golgi protein-73 (GOLPH2), carcinoembryonic antigen (CEA), vascular endothelial growth factor (VEGF), and matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) along with genomic driver mutations, miRNAs, lncRNAs, circulating tumor DNA (ctDNA) and circulating exosomes are presently being extensively studied for HCC diagnosis and prognosis, and treatment monitoring [101,102,103,104,105,106,107,108,109].