Estrogen receptor expression and docetaxel efficacy in patients with metastatic breast cancer: A pooled analysis of four randomized trials

Abstract

1046 Background:Differences in the efficacy of various chemotherapies in patients with estrogen receptor (ER) positive metastatic breast cancer are not well understood. In the present study, we assessed the efficacy of docetaxel in patients with metastatic breast cancer according to ER expression.Methods: The efficacy of docetaxel on response rates and progression-free survival were analyzed according to ER expression in four randomized trials that included a total of 1,631 patients. Odds-ratio for tumor response was estimated with logistic regression and hazard ratio for progression-free survival was estimated with Cox proportional hazards models. Results: ER expression was assessable in 1,037 patients included in these trials (64%). ER was expressed in 601 tumors (58%). Overall, docetaxel was associated with an increased response rate (odds ratio: 2.66, 95% CI: 1.83 to 3.87) and decreased hazard of disease progression (hazard ratio: 0.85, 95% CI: 0.73 to 0.97) compared to non-docetaxel containing therapy. Docetaxel was associated with similar improvement in response rate both in patients with ER-positive (odds ratio: 2.90, 95% CI: 1.72 to 4.87) and ER-negative disease (odds ratio: 2.55, 95% CI: 1.44 to 4.51). Among all ER-positive patients, tumor response rate was 31.1% among patients who did not receive docetaxel and 46.8% among patients who did receive docetaxel. Decreased hazard of disease progression due to docetaxel was also similar in ER-positive (HR: 0.82, 95% CI: 0.67–1.00) and ER-negative cancers (HR: 0.86, 95% CI: 0.70–1.07), but these results were heterogeneous among trials. The effect of docetaxel was not different in ER-positive and ER-negative disease, both in terms of response rates and progression-free survival (interaction test, p = 0.77 and p = 0.93). Conclusions: Docetaxel increases response rates and decreases the risk of disease-progression in a statistically similar extent both in patients with ER-positive and ER-negative metastatic breast cancer. No significant financial relationships to disclose.