CXCR4 is expressed on lymphocytes, hematopoietic stem cells, endothelial and epithelial cells, as well as multiple types of cancer cells, including breast cancer, ovarian cancer, prostate cancer pancreatic cancer, melanoma, esophageal cancer, lung cancer, bladder cancer, osteosarcoma, neuroblastoma, leukemia, gastric cancer, and nasopharyngeal carcinoma [22, 23]. The gene discussed is CXCR4; the disease is breast carcinoma.