Effect of dose-dense adjuvant chemotherapy in hormone receptor positive/HER2-negative early breast cancer patients according to immunohistochemically defined luminal subtype: an exploratory analysis of the GIM2 trial.

Background: Luminal A-like and luminal B-like subtypes have different sensitivity to (neo)adjuvant chemotherapy, but their role in predicting dose-dense (DD) efficacy in the high-risk setting is unknown. In this exploratory analysis of the Gruppo Italiano Mammella 2 (GIM2) trial, we investigated DD efficacy according to luminal-like subtypes.
Methods: Patients with node-positive early breast cancer were randomised to receive either DD or standard-interval (SI) anthracycline-based chemotherapy followed by paclitaxel. In our analysis, luminal A-like cohort was identified as having a Ki67 < 20% and a progesterone receptor (PgR) ≥ 20%; luminal B-like cohort as having a Ki67 ≥ 20% and/or a PgR < 20%.
Results: Out of 2003 patients enrolled in the GIM2 trial, 412 had luminal A-like and 638 luminal B-like breast cancer. After a median follow-up of 7.9 years, disease-free survival (DFS) was 80.8% (95% confidence interval [CI] 76.4-84.5) and 70.5% (66.5-74.2) in luminal A-like and luminal B-like cohorts; overall survival (OS) was 91.6% (88.2-94.1) and 85.1% (81.7-87.9), respectively. We found no significant interaction between treatment and luminal subtype (interaction p = 0.603 and 0.535 for DFS and OS, respectively). When DD efficacy was investigated separately in each cohort, luminal-B like cohort appeared to benefit more from the DD schedule both in terms of DFS (unadjusted hazard ratio [HR] 0.72 [95% CI 0.54-0.96]) and OS (unadjusted HR 0.61 [95% CI 0.40-0.94]), compared with the luminal A-like cohort (unadjusted HR for DFS 0.89 [95% CI 0.59-1.33]; unadjusted HR for OS 0.83 [95% CI 0.45-1.54]).
Conclusions: No significant interaction between luminal-like subtype and treatment was observed. Patients in the luminal B-like cohort seemed to benefit more from DD schedule.
Competing Interests: Conflict of interest statement L.D.M. declares honoraria from Roche, Pfizer, Ipsen, Eli Lilly, Eisai, Novartis, Takeda and MSD and Seattle Genetics; a consulting and advisory role for Roche and Eli Lilly and fees for travel, accommodation and expenses from Roche, Pfizer and Celgene outside the submitted work. M.L. served as a consultant for Teva and received speaker honoraria from Theramex outside the submitted work. O.G. received personal fees from Celgene, Eisai, Pfizer, Amgen, Eli Lilly and Novartis; travel and accommodation expenses from Celgene, Roche and Pfizer and research funding from Eisai outside the submitted work. F.P. received honoraria for advisory boards, activities as a speaker, travel grants, research grants from Agmen, Celgene, Eli Lilly, Ipsen, MSD, Novartis, Pierre-Fabre, Pfizer and Takeda and received research funding from Astrazeneca, Eisai and Roche outside the submitted work. M.D.L. declares consulting fees from Pfizer, Novartis, Eli Lilly, Roche, Eisai and Celgene outside the submitted work.
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