CXCR4 and ovarian cancer: Frequencies of MDSCs closely correlated with CXCL12 and PGE-2 levels in ascitic fluid, and inhibition of COX-2 or PGE-2 receptors in MDSCs suppressed CXCR4 expression, and thus MDSC responsiveness to CXCL12 or ovarian cancer ascites (Obermajer et al., 2011).