We have prepared tissue micoarrays (TMAs) and performed IHC analyses of ER, PR, COX-2 and aromatase in primary tumor tissue from 88 of the 907 patients who participated in the multicenter randomized phase III P025 trial which compared first-line tamoxifen or letrozole treatment in postmenopausal women with locally advanced or metastatic breast cancer [2,3]. Here, ESR1 is linked to neoplasm.