Proteomic studies on PTC tissue from humans have suggested NTRK1, metalloproteinases (MMP-1, MMP-9 and MMP-13) and Cathepsins (-W and -X), NF-KB and other apoptosis associated proteins as radiation-induced PTC biomarkers, together with SPANXA as an important protein for thyroid cancer development [51–56]. Here, MMP9 is linked to thyroid cancer.