Purpose: Several adjuvant chemotherapy trials suggested that cytotoxic treatment is less effective in patients with estrogen receptor (ER)-positive breast cancers. The aim of the present study was to assess the efficacy of adjuvant docetaxel and anthracycline therapy according to ER expression in two randomized clinical trials.
Patients and methods: Pooled data from two randomized trials, BCIRG001 and PACS01, were examined. Hazard ratios for recurrence and survival were estimated by Cox proportional hazards models and were adjusted for clinical variables. Interaction between docetaxel and ER expression was tested.
Results: ER status was available for 3,329 patients (95% of all randomly assigned patients), of whom 75% (n = 2,493) were ER positive. Docetaxel therapy was associated with a 30% reduction in the risk of death (hazard ratio [HR] = 0.70; 95% CI, 0.54 to 0.91) in ER-positive patients and a 31% reduction (HR = 0.69; 95% CI, 0.52 to 0.94) in ER-negative patients. Docetaxel therapy was associated with a 21% reduction in the risk of recurrence (HR = 0.79; 95% CI, 0.66 to 0.93) in ER-positive patients and a 31% reduction (HR = 0.69; 95% CI, 0.54 to 0.97) in ER-negative patients. The interaction between docetaxel therapy and ER status was not statistically significant for either overall survival (P = .87) or disease-free survival (P = .30). ER expression was also not predictive for docetaxel efficacy when it was analyzed as a semi-continuous variable based on percent of positive cells by immunohistochemistry (test for heterogeneity, P = .56 and .86 for overall survival and disease-free survival, respectively).
Conclusion: In the pooled analysis of these two trials, docetaxel did not have a statistically significantly different effect on the risk of recurrence or death in ER-positive and ER-negative patients.