Estrogen receptorpositive, progesterone receptor-negative breast cancer: Association with growth factor receptor expression and tamoxifen resistance

Background: Clinical data indicate that estrogen receptor – positive/progesterone receptor – negative (ER + /PR − ) breast cancers are less sensitive to tamoxifen than are ER + /PR + tumors. It has also been reported that tamoxifen may be less effective in tumors that overexpress either HER-2 or HER-1 (epidermal growth factor receptor) and that signaling through these receptors reduces PR expression in experi-mental models. We hypothesized that ER + /PR − breast tumors are more likely than ER + /PR + breast tumors to have an aggressive phenotype, to express HER-1 and overexpress HER-2, and are less likely to benefi t from tamoxifen adju-vant therapy. Methods: Clinical and biological features of 31 415 patients with ER + /PR + tumors were compared with those of 13 404 patients with ER + /PR − tumors. Association between disease-free survival (DFS) and HER-1 and HER-