During prostate cancer metastasis, a CXCL12-rich niche is reported to facilitate colonization at a secondary site (particularly in the bone) and CXCR4-CXCL12 signaling plays a key role in mediating tumor–stroma interactions required for prostate cancer cells to grow in the presence of chemotherapeutic agents [189,284,287]. The gene discussed is CXCR4; the disease is prostate cancer.