MMP14 and breast cancer: Additionally, analysis of MT1-MMP protein levels in the 21 T cell lines mammary tumour progression series demonstrated that breast cancer cells which represent ADH and DCIS mammary tumours produce high levels of active MT1-MMP protein, whereas invasive 21MT-1 IMC cells produce undetectable levels of MT1-MMP, an observation that is consistent with our findings using MCF-7 C3 cells and our overall conclusion that low levels of MT1-MMP may better represent metastatic cancer.