Detailed study of the underlying molecular mechanisms reveal that cancer cell CXCR4 overexpression contributes to aggressive tumor behavior, tumor growth, invasion, angiogenesis, metastasis, relapse, and therapeutic resistance [33–35], and upregulated expression of CXCR4 was an independent prognostic predictor for patients with gastric cancer [36]. The gene discussed is CXCR4; the disease is gastric cancer.