Prostate cancer most commonly spreads to bone. Despite newer therapies which prolong the survival of patients with bone metastasis, they remain incurable. Patients newly diagnosed with prostate cancer can already have tumor cells in their bones, but some of these patients never develop bone metastasis, while others do develop tumor growth in their bone but many years later. This suggests that the bone environment normally does not permit tumor cells to grow and keeps prostate cells in a ‘dormant state’. Certain types of cells or biological processes in the bone may talk to prostate tumor cells and keep them ‘dormant’ thereby preventing their growth. However, prostate tumors eventually bypass these blocks in part by activating processes such as new blood vessel growth to feed the growing tumor, activating bone degradation to release factors that support tumor cell growth, and by retraining immune cells so they cannot recognize and kill tumor cells. We have identified apathway in prostate tumor cells that may regulate this cell communication and reprograming in the bone, and we will test how this pathway allows prostate tumor cells to ‘reprogram’ the bone environment to support tumor growth.