Final 10-year results of the Breast International Group 2-98 phase III trial and the role of Ki67 in predicting benefit of adjuvant docetaxel in patients with oestrogen receptor positive breast cancer.

Aim: Breast International Group (BIG) 2-98 is a randomised phase III trial that tested the effect of adding docetaxel, either in sequence to or in combination with anthracycline-based adjuvant chemotherapy, in women with node-positive breast cancer (BC). Here, we present the 10-year final trial safety and efficacy analyses. We also report an exploratory analysis on the predictive value of Ki67 for docetaxel efficacy, in the BIG 2-98 and using a pooled analysis of three other randomised trials.

Patients And Methods: 2887 patients were randomly assigned in a 2×2 trial design to one of four treatments. The primary objective was to evaluate the overall efficacy of docetaxel on disease free survival (DFS). Secondary objectives included comparisons of sequential docetaxel versus sequential control arm, safety and overall survival (OS). Ki67 expression was centrally evaluated by immunohistochemistry.

Results: After a median follow-up of 10.1years, the addition of docetaxel did not significantly improve DFS or OS (hazard ratio (HR)=0.91, 95% confidence interval (CI)=0.81-1.04; P=0.16 and HR=0.88, 95% CI=0.76-1.03; P=0.11, respectively). Sequential docetaxel did not improve DFS compared to the sequential control arm (HR=0.86, 95% CI=0.72-1.03; P=0.10). In oestrogen receptor (ER)-positive tumours with Ki67⩾14%, the addition of docetaxel resulted in 5.4% improvement in 10-year OS (P=0.03, test for interaction=0.1). In a multivariate model, there was a trend for improved DFS and OS in ER-positive patients with high Ki67 and treated with docetaxel (HR=0.79, 95% CI=0.63-1.01; P=0.05 and HR=0.76, 95% CI=0.57-1.01; P=0.06, respectively). A pooled analysis of four randomised trials showed a benefit of taxanes in highly proliferative ER-positive disease but not in low proliferating tumours (interaction test P=0.01).

Conclusion: The DFS benefit previously demonstrated with sequential docetaxel is no longer observed at 10years. However, an exploratory analysis suggested a benefit of docetaxel in patients with highly proliferative ER-positive BC.