['Although there is evidence for interaction between epidermal growth factor receptor (EGFR) and estrogen receptor (ER), it is still not clear how this affects response to endocrine therapies like tamoxifen. Here we assess the relationship between EGFR expression and tamoxifen response, with a new quantitative technology.', 'A tissue microarray was constructed from breast cancer from a cohort of 564 patients enrolled in a randomized clinical trial for adjuvant tamoxifen treatment in early breast cancer, with a median follow-up of 14 years. EGFR expression was measured using automated quantitative analysis, a fluorescence-based method for quantitative analysis of in situ protein expression.', 'In ER-positive patients, tamoxifen-treated patients with low EGFR expression (n = 113) showed a significant effect by 2 years of adjuvant tamoxifen (P = .01), in contrast to no treatment effect in the EGFR-high group (n = 73, P = .69). The untreated group showed 49% v 57% 10-year recurrence-free survival for EGFR low versus high (P = .466) in the corresponding group of ER-positive patients. A significant beneficial effect of tamoxifen treatment was seen in the EGFR-low group (hazard ratio [HR] = 0.43 (95% CI, 0.22 to 0.84; P = .013) in contrast to no effect in the EGFR-high group (HR = 1.14; 95% CI, 0.59 to 2.22; P = .7) by using a Cox model.'] Is quantitative measurement of epidermal growth factor receptor a negative predictive factor for tamoxifen response in hormone receptor positive premenopausal breast cancer?