Pairwise comparisons were made between PIN, GP3, GP4, GP5 and LN metastases and normal epithelium, respectively, using the limma package implemented in R to identify differentially expressed probe sets. Expression patterns of probe sets that are common or unique in GP3, GP4, GP5 and LN metastatic tissues are summarized in a 4 way Venn diagram. A detailed description of probe set tissue distribution is listed in Table S5.