CCL21 and lung cancer: Cochrane’s Q test did not provide evidence of heterogeneity between CCL14 (p = 0.916), CCL19 (p = 0.446), CCL20 (p = 0.130), CCL21 (p = 0.878), CCL27 (p = 0.762), CXCL9 (p = 0.340) and CXCL13 (p = 0.770) and lung cancer.