Correlation Map. The Spearman rank correlation coefficient rho for the supervised list of differentially expressed genes, evaluated between all different pairs of tumour samples. The results are plotted using the levelplot function of R. The colour legend on the right hand side of the figure indicates that bright yellow corresponds to a value of rho nearly equal to one, whereas bright blue is assigned to values of rho close to 0.85. No values of rho less than 0.85 are obtained. The resistant patients are given patient identifiers between 1 and 12, whereas the sensitive patients are given patient identifiers between13 and 28. This pair-wise display of all 28 samples clearly shows the similarity in expression profiles of all tumours within the 12 tumour resistant group, which can clearly be distinguished from the similarities of expression of all tumours within the 16 tumour sensitive group. The high degree of homogeneity within each of these two groups, and the dissimilarities between the resistant and sensitive tumour groups, provides strong evidence for the robustness of the identification and statistical evaluation of the 204 differentially expressed genes.