Cancer cells secrete soluble factors and chemokines that recruit bone marrow derived cells (BMDC) toward sites of future metastasis formation. Recently, not only soluble factors but also small vesicles (exosomes, 30-100 nm) were described, which contain mRNAs, miRNAs and polypeptides from their cell of origin. These exosomes from the cancer cells are instrumental for BMDCs to prepare the premetastatic niche.