Wang RX, et al. - Whether it is clinically useful to monitor serum (sMMP-9) and histological MMP-9 (hMMP-9) during neoadjuvant chemotherapy (NAC) for triple-negative breast cancer (TNBC) was assessed in this study including 303 TNBC patients who received weekly paclitaxel plus carboplatin treatments before surgical resection. Using enzyme-linked immunosorbent assay (ELISA), sMMP-9 was measured at baseline and before surgery. Using immunohistochemistry, hMMP-9 expression in patients with residual tumors after NAC was identified. Findings revealed that TNBC patients who will respond to NAC and will display varying risks of disease relapse could be identified by monitoring serum MMP-9 and histological MMP-9. Therefore, MMP-9 could be a predictive and prognostic biomarker for customizing and adjusting NAC strategy for TNBC.