Estrogen-responsive genes identified in cell-line studies were also differentially expressed in ER+ breast tumors compared to ER- tumors. Estrogen-responsive gene-expression profiles are compared to the composite expression ratio for those genes in each of the six breast tumor studies surveyed (L.D.M., B.M.F. Mow, L.A.V., and E.T.L., unpublished work and [36-40]). Differentially expressed genes were defined by p < 0.01 between ER+ and ER- tumor samples. Genes that responded similarly in ER+ tumors and in vitro following E2 treatment are highlighted in magenta.