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

Background. Differences in the efficacy of various chemotherapies in patients with estrogen receptor (ER)⁺ 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 in terms of the response rate and progression-free survival (PFS) time was analyzed according to ER expression in four randomized trials comparing a docetaxel-based regimen with a nontaxane regimen that included a total of 1,631 patients. The odds ratio for tumor response was estimated with logistic regression and a hazard ratio (HR) for PFS was estimated with Cox proportional hazards models. Findings. ER expression was assessable in 1,037 patients included in these trials (64%). ER was expressedin 601 tumors (58%). Docetaxel was associated with a similarlyhigherresponserateinbothpatientswithER (odds ratio, 2.90; 95% confidence interval [CI], 1.72-4.87) and patients with ER (odds ratio, 2.55; 95% CI, 1.44-4.51) disease. The lower hazard for disease progression with docetaxel was also similar in ER (HR, 0.82; 95% CI, 0.67-1.00) and ER (HR, 0.86; 95% CI, 0.70-1.07) cancers. The effect of docetaxel was not different in ER⁺ and ER^- disease, in terms of both the response rate and PFS time (interaction test, p.77andp.93).Interpretation. Docetaxel produces a higher response rate and lower risk for disease progression to a statistically similar extent in both patients with ER⁺ and patients with ER^- metastatic breast cancer.