Expression data from six breast cancer microarray studies (L.D.M., B.M.F. Mow, L.A.V., and E.T.L., unpublished work and [36-40]) were mined for genes that were differentially expressed (p-value < 0.01 false discovery rate, ER+ vs ER-) in human breast tumor samples with respect to ER status. The gene discussed is ESR1; the disease is breast cancer.