Analysis of CXCR4 and CXCR7 in cell lines and clinical data on association with recurrence of oestrogen receptor–positive breast cancer. wt-MCF7, MCF7-LTED, wt-SUM44 and SUM44-LTED cells were transfected with siCXCR4 (A) or siCXCR7 (B) versus sicontrol × exogenous oestradiol (E2) (1 nM). Cells were cultured for 6 days. Cell survival was measured using CellTiter-Glo. The data are expressed as fold changes relative to sicontrol. Each treatment was carried out with eight replicates. The data shown are representative of a minimum of five independent experiments. Bars represent × standard error of the mean (SEM). *P <0.05, **P <0.01, ***P <0.001. (C) Kaplan-Meier analysis of the influence of CXCR4 and CXCR7 on relapse-free survival (RFS) in patients with oestrogen receptor–positive (ER+) breast cancer (BC), who were either treatment-na–ve or treated with tamoxifen, whose data were derived from publicly available clinical BC data sets collected over 12 years . Data were stratified by the highest quartile versus the rest. CXCR, Chemokine C-X-C receptor; DCC, Dextran-coated charcoal; LTED, Long-term oestrogen deprivation; si, Small interfering; wt, Wild type.