MT4 and breast cancer: In a study by Cabottaux et al, higher expression of MT4-MMP protein in breast cancer was related to metastatic lymph nodes.34 What is surprising is that in their functional study, higher expression of recombinant MT4-MMP in the breast cancer cell line (MDA-MB-231) did not influence cell proliferation or invasion but contributed to tumor growth and progression of lung metastases when inoculated in RAG-1 immunodeficient mice.