CXCR4 and neoplasm: Funnel plots evaluating hypoxia marker prevalence rates according to tumor grade showed no evidence for publication bias for GLUT1 and CXCR4 (all Egger’s tests p > 0.25), but indicated that smaller studies showed a larger increase in CAIX prevalence for grade III versus I and a larger decrease in IGF1R prevalence for grade II versus grade I tumors (i.e. more extreme effects in small studies; Egger’s tests p = 0.044 and p = 0.023, respectively).