Therefore, the physiological relevance of extreme changes in expression levels, such as our ~17,000 fold change in MT1-MMP mRNA seen in our transient transfectants, or ~1500 fold change in stable cell lines, would be difficult to reconcile with primary human breast cancers which have a ~1.7 to 3.2 fold change in MT1-MMP mRNA expression. This evidence concerns the gene MMP14 and breast carcinoma.