Based on our previous observations that primary breast cancers of molecularly defined subtypes differentially expressed members of the COX-2/PGE2 pathway at the mRNA level, we characterized a panel of breast cancer cell lines reflecting breast cancer subtypes to further test the hypothesis that aggressive, metastatic, and basal type breast cancers would display a pattern of COX-2 pathway expression leading to high PGE2 in the tumor microenvironment. This evidence concerns the gene PTGS2 and breast carcinoma.