Abstract HER2-02: HER2-02 HER2-Low Status is Associated with Worse Clinical Outcomes in Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer Patients Treated With First-Line Cyclin-Dependent Kinase 4/6 Inhibitors Plus Endocrine Therapy

Abstract

Abstract Introduction: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) are the standard first-line treatment for patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (HR+/HER2- aBC). HER2-low BC, which is defined by an IHC score for HER2 of 1+ or 2+ with negative ISH assay, accounts for more than half of all HR+/HER2- aBC cases, and it is associated with remarkable clinical benefit from the novel anti-HER2 antibody drug conjugate (ADC) trastuzumab-deruxtecan. Evidence on the prognostic impact of HER2-low status is controversial in both limited-stage and advanced BC. Here, we sought to investigate the possible prognostic relevance of HER2-low status in a population of aBC patients treated with CDK4/6i plus ET. Methods: We conducted a retrospective-prospective study in six Italian Cancer Centers to investigate the impact of HER2 status (low vs. 0) on the progression-free survival (PFS) and overall survival (OS) of consecutive HR+/HER2- aBC patients treated with CDK4/6i plus ET (aromatase inhibitors or fulvestrant) as a first-line therapy. In the main study analysis, we considered HER2 status in the last tumor assessment (i.e., primary tumor, or, when available, a metastatic lesion). We also performed a subgroup analysis including only patients with HER2 status evaluation in a metastatic lesion collected before CDK4/6i plus ET therapy initiation. The association between HER2 status (low vs. 0) and PFS or OS was evaluated using log-rank test and Cox regression modeling. Results: We evaluated 767 consecutive HR+/HER2- aBC patients treated with CDK4/6i plus ET between January 2017 and January 2022. Of these, 436 patients (56.8%) received CDK4/6i plus ET as a first-line therapy, and they were included in this analysis. Median age was 63 years (range 27-87), and 362 patients (83.0%) were postmenopausal. The majority of patients were treated with palbociclib (68.3%), while 91 (20.9%) and 47 (10.8%) patients received ribociclib and abemaciclib, respectively. Regarding HER2 status, 269 (62.9%) patients had HER2-low tumors, while 159 (37.1%) patients had HER2-0 neoplasms. HER2-low status was associated with significantly lower PFS when compared to HER2-0 status [median PFS (mPFS) 23.6 vs. 32.3 months, respectively; p=0.014]. HER2-low status was also associated with significantly worse OS (mOS 48.7 vs 58.3 months, respectively; p=0.025). These results were confirmed in multivariable models adjusting the impact of HER2 status for clinically-relevant covariates, namely estrogen receptor status, Ki-67, age, number of metastatic sites, presence of liver metastases, disease free interval, ECOG Performance Status. In this analysis, HER2-low status, compared with HER2-0 status, was independently associated with worse PFS [adjusted Hazard Ratio (aHR): 1.62; 95% confidence interval (CI): 1.17-2.24; p< 0.01] and OS (aHR: 1.74; 95% CI: 1.09-2.76; p=0.019). Subgroup analysis conducted in the subset of 256 patients with available metastatic tumor samples collected before CDK4/6i plus ET initiation confirmed that HER2-low status (n=157), when compared to HER2-0 status (n=99), was independently associated with worse PFS (mPFS 24.5 vs 35.2 months, p=0.01; aHR 2.07; 95% CI: 1.28-3.34, p< 0.01) and worse OS (mPFS 48.7 vs 72.3 months, p=0.027; aHR 3.12; 95% CI 1.44-6.77, p< 0.01). Conclusions: This multicenter Italian study revealed that HER2-low status has independent, negative prognostic value in patients with HR+/HER2- aBC treated with CDK4/6i plus ET in the first-line setting. Our results suggest that HER2-low status might be associated with different clinical benefit from standard anticancer therapies in specific clinical settings. The definition of treatment algorithms also taking into account HER2 status is a clinical priority in patients with HR+/HER2- aBC. Citation Format: Emma Zattarin, Caterina Sposetti, Rita Leporati, Luigi Mariani, Alice Menichetti, Chiara Corti, Chiara Benvenuti, Giovanni Fucà, Riccardo Lobefaro, Francesca Ligorio, Daniele Presti, Leonardo Provenzano, Andrea Vingiani, Gaia Griguolo, Marianna Sirico, Ottavia Bernocchi, Antonio Marra, Paola Zagami, Elisa Agostinetto, Flavia Jacobs, Pierluigi Di Mauro, Andrea Esposito, Carlo Alberto Giorgi, Luca Lalli, Laura Boldrini, Pier Paolo Maria Berton Giachetti, Ambra Carnevale Schianca, Valentina Guarneri, Rebecca Pedersini, Agnese Losurdo, Alberto Zambelli, Daniele Giulio Generali, Giuseppe Curigliano, Giancarlo Pruneri, Filippo de Braud, Maria Vittoria Dieci, Claudio Vernieri. HER2-02 HER2-Low Status is Associated with Worse Clinical Outcomes in Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer Patients Treated With First-Line Cyclin-Dependent Kinase 4/6 Inhibitors Plus Endocrine Therapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-02.