"Cancer" is a disease that can spread to the other organs over time. The prognosis of cancer patients with metastasis is generally poor. Accordingly, there is an urgent need to establish a greater understanding of metastatic processes. It is highly likely that cancer stem cells (CSCs) are the key cells that mediate metastases, even while the cellular origin of CSCs remains unknown. Growing evidence has also revealed that the microenvironment has profound effects on the regulation of CSCs. Recently, it has been shown that bone metastatic cancer cells target the microenvironment or 'niche' which houses hematopoietic stem cells (HSCs). The major function of the HSC niche is to maintain 'stemness' of HSCs. These findings suggest that by targeting the HSC niche metastatic cells parasitize the very foundation of hematopoiesis to maintain their stemness. These observations suggest that there will be a need to target the HSC niche to provide effective therapies to eradicate metastatic CSCs.