Molecular predictors of efficacy of adjuvant weekly paclitaxel in early breast cancer.

Treatment with fluororacil, epirubicin, and cyclophosphamide followed by weekly paclitaxel (FEC-P) yielded superior disease-free survival than FEC in the adjuvant breast cancer trial GEICAM 9906. We evaluate molecular subtypes predictive of prognosis and paclitaxel response in this trial. Two molecular subtype classifications based on conventional immunohistochemical and fluorescent in situ hybridization determinations were used: #1: Four groups segregated according to the combination of hormone receptor (HR) and HER2 status; #2: Intrinsic subtype classification (Triple Negative (TN), HER2, Luminal B and Luminal A).

Results: Both subtype classifications yielded prognostic and predictive information. HR +/HER2- patients (and Luminal A patients) had a significantly better outcome than the other subgroups of patients. The superiority of FEC-P over FEC was clearly more marked in HR-/HER2- patients (TN patients), particularly in the subset with basal phenotype (TN and either EGFR+ or cytokeratins 5/6+). The Luminal A subtype also achieved a significant benefit with FEC-P. The molecular-defined subgroup of TN was clearly predictive of better response to treatment with FEC-P. Luminal A patients had the best prognosis and also have a better outcome with weekly paclitaxel.