It is evident in our results that there are differences in the expression levels and their association with clinicopathological variables and survival outcomes when comparing the results from the centre versus periphery of the tumour mass. Effects of the sampling site on associations with tumor protein expression have been noted previously. For example, in an evaluation of biomarkers in ovarian cancer, Permuth-Wey et al reported sampling variability in protein expression analysis using tissue microarrays . The authors concluded that, for ovarian cancer at least, more reliable data were obtained from the TP than from the TC. This was attributed to optimal exposure to fixatives at the periphery of the processed tissues, although the effect of tumor heterogeneity on sampling variation should also be considered. For instance, TCs in general are more liable to hypoxia and necrosis compared to TP, and ischaemic injury may be another potential source for the biological differences seen within the same tumour.