Whereas Smollich et al.11 reported an association of NEP with disease-free survival and decreased metastasis, many other studies have implicated NEP as a potential biomarker of metastatic cancers.21, 22, 23, 24, 25 Our observation that NEP expression is suppressed in invasive breast cancer cells and IDC samples (Figure 1) and negatively regulates breast cancer invasion in vitro (Figure 2) are consistent with the clinical studies that correlate NEP expression with a better prognosis. Here, MME is linked to breast cancer.