Abstract
The bone marrow microenvironment is characterized by its multicellular nature, and perhaps less obviously by the high mobility of multiple transient and stationary cell lineages present in this environment. The trafficking of hematopoietic and mesenchymal cells between the bone marrow and blood compartments is regulated by a number of bone marrow-derived factors. It is suspected that transformed metastatic cells "hijack" these processes to engraft into the skeleton and eventually cause the skeletal complications associated with metastatic disease. In this short review, experimental and association data supporting the contribution of a less recognized cell type of the bone marrow - the nerves of the sympathetic nervous system - to early events of the breast cancer bone metastatic process, are summarized.