Similarly, our recent data demonstrate that CXCL12 binding to CXCR4 transactivates HER2 in PC cells to initiate chemo-invasive signaling and promotion of bone tumor growth, suggesting that this pathway is not only involved in initial seeding of bone metastases but also plays a key role in subsequent osseous expansion of metastases [10]. The gene discussed is CXCR4; the disease is bone neoplasm.