TGFB1 and gastric cancer: Because TGF-β1 is at least partly activated by proteolytic cleavage, we evaluated the total and active TGF-β1 levels for correlations with likely candidate proteinases involved in TGF-β1 activation and with PAI-1, a presumed secondary marker of TGF-β1 activity, in the gastric cancer homogenates (Table 3).