537 Background: It has been suggested that estrogen receptor (ER) expression is associated with relative resistance to adjuvant chemotherapy. The efficacy of adjuvant chemotherapy is still matter of controversy in this subset of patients. The aim of the present study was to assess the efficacy of docetaxel according to ER expression in adjuvant treatment trials. Patients and Methods: The efficacy of docetaxel according to ER expression was assessed in a pooled analysis of two randomized studies (BCIRG001 and PACS01) that included overall 3,490 patients with axillary node positive breast cancer. These studies compared either 3 (PACS01) or 6 (BCIRG001) cycles of a docetaxel-containing regimen, to a chemotherapy that did not contain docetaxel. Hazard ratios (HR) for death were determined by a Cox model adjusted for clinical characteristics (age, T size and number of lymph node involved). Interaction between docetaxel efficacy and ER expression was tested. Results: ER status was assessable in 3,329 patients (95%). The median age was 49 years old (range, 23–70). ER was expressed in 2,493 tumors (74%). In patients with assessable ER status (n=3329), docetaxel was associated with a significant reduction in the risk of death (HR=0.69; 95%CI: 0.51–0.92, p=0.01). Docetaxel therapy was associated with a 30% reduction in the risk of death in ER-positive disease (HR=0.70; 95%CI: 0.54–0.91) and a 31% reduction in the risk of death in ER-negative disease (HR=0.69; 95% CI: 0.52–0.94). Test for interaction did not detect any statistically significant difference in the relative effect of docetaxel according to ER status (HR for interaction=1.03; p=0.87). Conclusion: In this pooled analysis of two randomized trials, the relative effect of docetaxel on overall survival in adjuvant setting was not different between ER-positive and ER-negative disease. Docetaxel was associated with a significant risk reduction of death in patients with ER-positive disease. No significant financial relationships to disclose.