Examples of metastatic niches during early colonization of distant organs. (a) Systemic changes induced by the primary breast tumor: mobilization of VEGFR1+ bone marrow-derived cells (BMDCs), recruitment to the lungs, extracellular matrix (ECM) remodeling and formation of a pre-metastatic niche [107, 108]. The pre-metastatic niche promotes the colonization of breast cancer cells in the lungs. (b) Prostate cancer cells enter the osteoblastic niche, competing with hematopoietic stem cells (HSCs) for niche interactions in bone . CXCL12 chemokine promotes colonization of prostate cancer cells in the bone niche via CXCR4 interaction . (c) Breast cancer cells bringing their own niche material, tenascin C (TNC), to a distant site thereby promoting early colonization of the lungs . (d) Activated myofibroblasts produce the metastatic niche components TNC and periostin (POSTN), resulting in enhanced metastatic outgrowth [119–121]. VEGFR, vascular endothelial growth factor receptor.