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DOI: 10.1055/s-0045-1807783
Pathologic response in er-low early-stage breast cancer treated with neoadjuvant pembrolizumab plus chemotherapy
Authors
Background: Estrogen receptor-low (ER-low) breast cancer (BC) exhibits a tumor biology more similar to basal-like tumors than to luminal-like tumors. Despite patients with ER-low breast cancer having been excluded from the Keynote-522 study, they were included in trials evaluating neoadjuvant pembrolizumab (Keynote-526 trial) and nivolumab (CheckMate 7FL) for hormone receptor-positive BC. Although the ER-low subgroup was small, a benefit from neoadjuvant immunotherapy was suggested, with pathologic complete response (pCR) rates of 55.9% and 55.6% in the immunotherapy arms compared to 30.2% and 28.6% in the control arms, respectively.
Objective: To evaluate the outcomes of ER-low BC treated with neoadjuvant P+CT.
Methods: The real-world data (RWD) Neo-Real/GBECAM 0123 study is collecting data on patients with BC treated with neoadjuvant P+CT since July 2020 across ten Brazilian cancer institutions. In this analysis, we evaluated the clinical characteristics and efficacy outcomes of patients with ER-low BC, focusing on the rates of pCR and residual cancer burden (RCB) 0-1. ER-low was defined as estrogen receptor expression lower than 10% in immunohistochemistry.
Results: Among 410 patients included in this cohort to date, 14 had ER-low BC; 9 (64.3%) had stage II and 5 (35.7%) had stage III disease. The median age was 39.7 years (range 28 - 61). The majority of patients had grade 3 tumors (n = 13, 92.8%), and the median Ki67 index was 77% (range 30% - 90%). Thirteen patients completed the neoadjuvant therapy and underwent surgery. Among these, 8 (61.5%) achieved a pCR. The RCB 0-1 rate was also 61.5%; all five patients (38.5%) who did not achieve a pCR had RCB 2. Among 325 patients with ER-negative BC included in the same RWD study who had already undergone surgery, the pCR rate was 62.1%. With a median follow-up of 15.6 months, one patient in the ER-low group with residual disease had a recurrence. No recurrence was observed among the ER-low patients with a pCR.
Conclusion: In this cohort, ER-low BC represented a small subgroup enriched by tumors of high grade and high proliferative index. The pCR rates with neoadjuvant P+CT were comparable to those observed in TNBC. These results support the use of neoadjuvant immunotherapy for the ER-low subgroup.
Corresponding author: Renata Rodrigues da Cunha Colombo Bonadio (e-mail: rrccbonadio@gmail.com).
No conflict of interest has been declared by the author(s).
Publication History
Article published online:
06 May 2025
© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution 4.0 International License, permitting copying and reproduction so long as the original work is given appropriate credit (https://creativecommons.org/licenses/by/4.0/)
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Renata Colombo Bonadio, Flávia Cavalcanti Balint, Isadora Martins de Sousa, Ana Carolina Marin Comini, Monique Celeste Tavares, Fernanda Madasi, José Bines, Rafael Dal Ponte Ferreira, Daniela Dornelles Rosa, Candice Lima Santos, Zenaide Silva de Souza, Daniele Assad-Suzuki, Júlio Antônio Pereira de Araújo, Débora de Melo Gagliato, Carlos Henrique dos Anjos, Bruna M. Zucchetti, Anezka Ferrari, Mayana Lopes de Brito, Maria Marcela Fernandes Monteiro, Renata Cangussu, Paulo M. Hoff, Maria del Pilar Estevez-Diz, Laura Testa, Romualdo Barroso-Sousa. Pathologic response in er-low early-stage breast cancer treated with neoadjuvant pembrolizumab plus chemotherapy. Brazilian Journal of Oncology 2025; 21.
DOI: 10.1055/s-0045-1807783