Metastasis to bone is common in lung, kidney, breast and prostate cancers. However, prostate cancer is unique in that bone is often the only clinically detectable site of metastasis, and the resulting tumours tend to be osteoblastic (bone forming) rather than osteolytic (bone lysing). The interaction between host cells and metastatic cancer cells is an important component of organ-specific cancer progression. How can this knowledge lead to the development of more effective therapies?