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 expressed in 601 tumors (58%). Docetaxel was associated with a similarly higher response rate in both patients with ER(+) (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 = .77 and p = .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.