Abstract Purpose: Neoadjuvant chemotherapy is standard for high-risk HR+/HER2–breast cancer (BC). This study evaluates whether 12 months of letrozole plus abemaciclib could be an alternative. Patients and Methods: The phase II, open-label CARABELA trial randomized HR+/HER2− stage II-III BC patients with Ki-67 ≥20% to receive letrozole/abemaciclib for 12 months or chemotherapy for 6 months. Patients were stratified by menopausal status, TNM stage, and Ki-67 index (30% vs. ≥30%). The primary endpoint was the rate of residual cancer burden (RCB) 0–I. Secondary endpoints included clinical response rate (CRR) and correlations of Ki-67 and Recurrence Score® (RS) with tumor response. A Bayesian design aimed to assess treatment similarity. Results: 200 patients (median age 53 years, 57% postmenopausal, 79% stage II, 77% Ki-67 ≥30%, 58% RS ≥26) were randomized. RCB 0-I was achieved in 13% (letrozole/abemaciclib, 95% Credible Intervals (CrI): 7.4% − 20.5%) vs. 18% (chemotherapy, 95% CrI: 11.5% − 26.4%), failing to show similarity between treatment arms. The CRRs were 78% (letrozole/abemaciclib) vs. 71% (chemotherapy) (P=0.26). Tumors with Ki-67 ≥30% and/or RS results ≥26 showed a trend toward higher RCB 0–I rates with chemotherapy (23% vs. 17%, P=0.52). RCB 0-I rates were similar between treatments for tumors with Ki-67 30% or RS 26. Conclusions: CARABELA trial results suggest that 12 months of letrozole/abemaciclib may not offer similar efficacy to that of chemotherapy in achieving RCB 0–I. However, in less proliferative tumors (RS 26 or Ki-67 30%), outcomes were comparable, suggesting that letrozole/abemaciclib could replace (neo)adjuvant chemotherapy in selected patients.
Martín et al. (Fri,) studied this question.
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