Using an intraperitoneal ovarian tumor model (ID8-T) enriched for CD44+CD117+ cells with a cancer stem cell-like phenotype,6 we showed that intraperitoneal delivery of the CXCR4-A-armed vaccinia was more efficacious in inhibiting tumor growth compared with treatment with the soluble CXCR4-A (sCXCR4-A) counterpart or a systemic injection of the armed virus because of higher accumulation of the antagonist in tumors rather than in systemic tissues. This evidence concerns the gene CXCR4 and cancer.