Once educated by cancer cells, BM-MSCs secrete CXCL1, CXCL2, SDF1, IL-6, IL-8, TGFβ and microvesicles containing miRNA, such as miRNA-21 and miRNA-34a, all factors implicated in BC survival, progression and chemo-resistance (51, 52). Here, IL6 is linked to breast cancer.