CXCL12 and breast neoplasm: In previous study, we correlated SDF-1 expression in tumor tissue with presence of CTCs (manuscript submitted), and there was no correlation between epithelial CTCs and expression of SDF-1 in primary tumor tissue, nor correlation between plasma and tissue SDF-1 level (data not shown), suggesting, that source of plasma SDF-1, that attracts CTCs into circulation, is outside the primary breast tumor.