Based on the available data, the associations between CXCR4 over-expression and PFS were inconclusive in gastric cancer (1 studies, 26 patients, HR=3.42, 95% CI, 0.71-16.36) [53], head and neck cancer (1 studies, 71 patients, HR=1.19, 95% CI, 0.56-2.54) [56], lung cancer (2 studies, 233 patients, HR=1.05, 95% CI, 0.12-8.96) [8, 70], melanoma (2 studies, 103 patients, HR=1.42, 95% CI, 0.64-3.19) [73, 75], pancreatic cancer (1 studies, 71 patients, HR=1.28, 95% CI, 0.90-1.83) [85]. This evidence concerns the gene CXCR4 and head and neck cancer.