After treatment of neo-adjuvant systemic therapy in decreased expressions of C-erbB2 and CXCR4 in breast cancer, the findings are also biologically plausible since these functional proteins (i.e., apoptosis, invasion, metastasis, drug resistance/metabolism, proliferation) may represent effect, sensitivity and resistance to chemotherapy. The gene discussed is CXCR4; the disease is breast carcinoma.