MMP13 and neoplasm: Untreated high density mono-cultures of HCT116 expressed MMP-13, however compared to HCT116 high density tumor microenvironment co-cultures, expression was markedly lower (Fig. 5:a). These results are in agreement with other studies that expression of MMPs is known to be up-regulated in the tumor microenvironment [17]–[19], [41], known to be regulated by transcription factor NF-κB [36], [42].