The findings from this study might also lead to the hypothesis that, of the two MMPs, MMP9 is the predominant regulator of proBDNF proteolysis (Figure 6 and Figure 7) and resulting effect on cytotoxicity (Figure 8) and suggest that proteolytic cleavage of proBDNF by MMP9 represents a mechanism (Figure 9) by which the opposing actions of proBDNF and mBDNF may be regulated in the media of lung cancer cell lines. This evidence concerns the gene BDNF and lung carcinoma.