Guestini F, et al. - By analyzing a panel of molecules involved in key pathways of drug resistance and tumor progression before and after neoadjuvant chemotherapy (NAC) in triple-negative breast cancer (TNBC) patients, researchers intended to gain clarity on the underlying mechanisms. Participants were a total of 148 TNBC Japanese patients treated with anthracycline/taxane-based NAC. Before and after NAC, KI67, Topoisomerase IIα (TopoIIα), phosphatase and tensin homolog (PTEN), tumor protein 53 (p53), B-cell lymphoma 2 (Bcl2), vimentin, breast cancer resistance protein encoded by the gene ABCG2 (ABCG2/BCRP1), multidrug resistance 1 encoded by the gene ABCB1 (ABCB1/MDR1), and multidrug resistance protein 1 encoded by the gene ABCC1 (ABCC1/MRP1) were immunolocalized in surgical pathology materials. According to findings, treatment response and/or eventual clinical outcomes could be predicted by KI67, TopoIIα, PTEN, and ABCC1/MRP1 status. Insight into the mechanisms of drug resistance and relapse of TNBC patients receiving NAC was possible via these findings.