Abstract HER2-15: HER2-15 Retrospective Study to Estimate the Prevalence and Describe the Clinicopathological Characteristics, Treatment Patterns, and Outcomes of HER2-Low Breast Cancer

Background: About 60% of breast cancers (BCs) traditionally categorized as HER2 negative (HER2-neg; immunohistochemistry [IHC] 0, IHC 1+ or IHC 2+/in situ hybridization [ISH]–) express low levels of HER2 (HER2-low; IHC 1+ or IHC 2+/ISH–; Schettini, NPJ Breast Cancer 2021). In the phase 3 DESTINY-Breast04 trial (NCT03734029), trastuzumab deruxtecan (T-DXd) showed significantly longer progression-free survival and overall survival (OS) vs physician’s choice of chemotherapy in patients (pts) with HER2-low metastatic BC (mBC) who previously received chemotherapy (Modi, NEJM 2022). As HER2-low becomes a clinically relevant HER2 status among pts with BC, greater understanding of pts with HER2-low disease is needed, including identification of these pts using conventional IHC assays. Our objectives were to assess the prevalence of HER2-low among HER2-neg mBC based on rescored HER2 IHC slides, to describe characteristics of pts with HER2-low mBC, and to characterize concordance between historical HER2 scores and rescores. Methods: This global, multicenter, retrospective study (NCT04807595) included pts with confirmed HER2-neg (HER2 IHC 0, 1+, or 2+/ISH−) unresectable/mBC diagnosed from 2014 through 2017. HER2 IHC-stained slides were rescored after training on low-end expression scoring using Ventana 4B5 and other assays by local laboratories at 13 sites in 10 countries blinded to historical HER2 scores. BCs were categorized as HER2-low (IHC 1+ or IHC 2+/ISH−) or HER2 IHC 0 (IHC 0 or >0< 1+). Prevalence of HER2-low and concordance between historical HER2 scores and rescores were assessed. Demographics, clinicopathological characteristics, treatment patterns, and outcomes were examined via data from medical charts/health records. Results: HER2 rescores were obtained for 781 pts with HER2-neg mBC. HER2-low prevalence was 67.1% overall; 71.1% in hormone receptor (HR)–positive (HR+) and 52.5% in HR–negative (HR−) subgroups. There were no notable differences in characteristics (Table) or treatment patterns between pts with HER2-low and HER2 IHC 0. The most frequent therapies used in the first treatment in the metastatic setting were endocrine therapy (64.1%) for pts with HR+ mBC and chemotherapy (94.4%) for pts with HR− mBC. Among pts with HR+ mBC, 10.2% received cyclin-dependent kinase 4/6 inhibitors as part of their first treatment. There were no statistically significant differences in clinical outcomes between the HER2-low and HER2 IHC 0 groups within each HR subgroup. For pts with HR+ mBC, median time to first subsequent treatment was 10 and 8 months for the HER2-low and HER2 IHC 0 groups, respectively. Overall, concordance was 81.2% (kappa=0.582). Concordance between historical HER2 scores and rescores was 87.3% for HER2-low and 70.1% for HER2 IHC 0 samples. Conclusions: The prevalence of HER2-low (67.1%) among pts previously categorized as HER2-neg mBC in this study was similar to that of an earlier study (≈60%). No obvious differences in patient characteristics or clinical presentation were seen between pts with HER2-low and HER2 IHC 0 mBC. Overall percentage agreement between rescored and historical HER2 scores was 81.2%; agreement was numerically greater for HER2-low than HER2 IHC 0. As HER2-targeted therapies such as T-DXd for the treatment of pts with HER2-low BC are emerging, a greater understanding of pts with HER2-low expression who may benefit from these therapies is important.

Citation Format: Giuseppe Viale, Mark Basik, Naoki Niikura, Eriko Tokunaga, Sara Brucker, Frédérique Penault-Llorca, Naoki Hayashi, Joo Hyuk Sohn, Rita Teixeira de Sousa, Adam M. Brufsky, Ciara S. O’Brien, Fernando Schmitt, Gavin Higgins, Della Varghese, Gareth D. James, Akira Moh, Andrew Livingston, Victoria de Giorgio-Miller. HER2-15 Retrospective Study to Estimate the Prevalence and Describe the Clinicopathological Characteristics, Treatment Patterns, and Outcomes of HER2-Low Breast Cancer [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 HER2-15.

Abstract OT1-01-01: A randomised phase II trial of palbociclib and fulvestrant vs standard endocrine therapy in patients with ER positive HER2 negative breast cancer and ctDNA detected molecular relapse during adjuvant endocrine therapy (TRAK-ER)

Background: Most patients with early stage oestrogen receptor positive (ER+) and HER2 negative breast cancer will be cured of their cancer. However, up to 20% of patients may experience disease recurrence in the first 10 years. Molecular relapse of ER+ breast cancer can be detected with circulating tumour DNA (ctDNA) before clinical relapse occurs. Palbociclib, a CDK4/6 inhibitor, plus fulvestrant, a selective oestrogen receptor degrader, is a standard first line therapy for patients with ER+ breast cancer who have relapsed on standard endocrine therapy. We designed TRAK-ER to establish a surveillance system for ctDNA detection and then to assess whether treating patients, who have ctDNA detected molecular relapse, with palbociclib and fulvestrant may defer or prevent relapse. Design: TRAK-ER is a phase 2 multi-centre, randomised, open-label parallel superiority trial in patients with ER+ early breast cancer, recruiting at centres in the UK and France. In the surveillance phase patients will be monitored for molecular recurrence with ctDNA testing. To be eligible for the surveillance phase patients must be aged 18 or over, have ER+ (≥10% or Allred score 6/8 or greater) and HER2 negative breast cancer and have completed their primary surgery, chemotherapy and radiotherapy. Standard endocrine therapy (GnRH analogues, aromatase inhibitors and tamoxifen) must have been received for a minimum of 6 months and a maximum of 7 years and be planned to continue for at least another 3 years. Inclusion criteria in patients who did not receive neoadjuvant chemotherapy are at least one of: (a) four or more involved axillary or positive supraclavicular lymph node; (b) tumour size >5cm; (c) one to three involved axillary lymph nodes together with at least one of: tumour size >3cm, grade 3 or a high genomic risk score. Patients who received neoadjuvant chemotherapy require at least one lymph node positive or a tumour size >3cm after chemotherapy. Invitae Personalized Cancer Monitoring (PCM TM) will be used for ctDNA analysis, a pan-cancer, tumour-informed liquid biopsy test that uses next-generation sequencing to detect minimal or molecular residual disease (MRD) in solid tumours. ctDNA analysis will be every 3 months for up to 3 years. Detection of ctDNA will trigger staging imaging. If no overt metastatic disease is identified, patients will be able to enter the treatment phase of the study, and be 1:1 randomised using minimisation to either remain on standard endocrine therapy or switch to palbociclib plus fulvestrant. Those who are allocated to remain on endocrine therapy are allowed to continue on the same therapy or change standard endocrine therapy. Duration of palbociclib and fulvestrant will be 2 years, or until relapse. Up to 1300 patients will enrol for tissue screening to allow 1100 patients to enter into ctDNA surveillance. 132 patients will enter the treatment part of the study. The primary endpoint of the surveillance phase is ctDNA detection rate. The primary endpoint of the treatment phase is relapse free survival (RFS). RFS will be calculated in the intention to treat population using Kaplan Meier methods from the date of randomisation to the date of recurrence or death from any cause. Secondary endpoints include relapse free interval, invasive disease free survival, distant recurrence free survival, overall survival and ctDNA clearance. (NCT04985266)

Citation Format: Nicholas Turner, Edward R. Phillips, Catey Bunce, Marie Robert, Caroline Bailleux, Isaac Garcia-Murillas, Komel Khabra, Iain Macpherson, Ciara S. O’Brien, Alicia F. Okines, Carlo Palmieri, Peter Schmid, Claire Swift, Sabrina Yara, Simon Connolly, Jérôme Lemonnier, Dymphna Lee, Fabrice Andre. A randomised phase II trial of palbociclib and fulvestrant vs standard endocrine therapy in patients with ER positive HER2 negative breast cancer and ctDNA detected molecular relapse during adjuvant endocrine therapy (TRAK-ER) [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 OT1-01-01.

Abstract P3-07-28: SERENA-1: Updated analyses from a Phase 1 study of the next generation oral selective estrogen receptor degrader camizestrant (AZD9833) combined with abemaciclib, in women with ER-positive, HER2-negative advanced breast cancer

Background: SERENA-1 (NCT03616587) is a Phase 1, multi-part, open-label study of camizestrant in women with ER+/HER2− advanced breast cancer. Parts A/B and C/D (escalation/expansion) examined camizestrant as monotherapy and in combination with palbociclib respectively and have been presented previously.1,2 Here we present data from parts G/H which examined camizestrant in combination with abemaciclib. Methods: The primary objective was to determine the safety and tolerability of camizestrant 75 mg once daily (QD) in combination with abemaciclib 150 mg twice daily (BID). Secondary objectives included investigation of anti-tumor response and pharmacokinetics (PK). Participants were previously treated women of any menopausal status (pre-menopausal women received this combination alongside ongoing ovarian function suppressors). Prior treatment with ≤2 lines of chemotherapy in the advanced setting was permitted. There was no limit on the number of lines of prior endocrine treatment in the advanced setting; previous treatment with CDK4/6 inhibitors (CDK4/6i) and fulvestrant was permitted. Results: As of 1st June 2022, 24 patients had received camizestrant in combination with abemaciclib with a median 7.7 month follow up. Tolerability of the combination of camizestrant and abemaciclib was consistent with that of each drug individually. No patient required camizestrant dose reduction. All camizestrant-related heart rate decreases were Grade 1 (asymptomatic). PK data for camizestrant in combination with abemaciclib were consistent with camizestrant as monotherapy and published abemaciclib steady-state PK data, indicating no clinically relevant drug-drug interaction. In these heavily pre-treated patients (46% prior chemotherapy, 75% prior CDK4/6i, 54% prior fulvestrant; all in the advanced disease setting) and of whom 67% had visceral metastases, the objective response rate was 5/19 (26.3%), the clinical benefit rate at 24 weeks was 16/24 (66.7%) and the median progression-free survival had not been reached, with 8/24 patients experiencing a progression event. These data support the use of camizestrant 75 mg QD combined with the approved abemaciclib dose. Conclusions: Camizestrant 75 mg QD in combination with abemaciclib 150 mg BID was well tolerated with encouraging clinical activity. The inclusion of this regimen in the ongoing Phase 3, SERENA-6 trial 3, of camizestrant combined with CDK4/6i versus an aromatase inhibitor, will further clarify the role of this combination in the treatment of patients with ER+/HER2− advanced breast cancer with tumors expressing ESR1 mutations. References 1. Baird R, Oliveira M, Ciruelos Gil EM, et al. SABCS 2020 Virtual Meeting. Abstract PS11-05. 2. Oliveira M, Hamilton EP, Incorvati J, et al. J Clin Oncol 40, 2022 (suppl 16; abstr 1032). 3. SERENA-6 trial. Available at https://clinicaltrials.gov/ct2/show/NCT04964934 We acknowledge Helen Heffron, PhD, from InterComm International who provided medical writing support funded by AstraZeneca.

Citation Format: Nicholas Turner, Christos Vaklavas, Emiliano Calvo, Javier Garcia-Corbacho, Jason Incorvati, Manuel Ruiz Borrego, Chris Twelves, Anne Armstrong, Begoña Bermejo, Erika Hamilton, Mafalda Oliveira, Eva Ciruelos, Peter Kabos, Manish R Patel, Maria Borrell, Howard Burris, Bruno de Paula, Alejandro Falcon, Cristina Hernando, Irene Moreno, Ciara S. O’Brien, Elena Shagisultanova, Ivan Victoria Ruiz, Judy S. Wang, Mei Wei, Tim Brier, Danielle Carroll, Carmela Ciardullo, Lisa Gibbons, itziar irurzun-Arana, Tony Jack, bistra kirova, Teresa Klinowska, Justin Lindemann, Julie Maidment, Alastair Mathewson, Rhiannon Maudsley, Robert McEwen, Christopher Morrow, Andy Sykes, Richard D. Baird. SERENA-1: Updated analyses from a Phase 1 study of the next generation oral selective estrogen receptor degrader camizestrant (AZD9833) combined with abemaciclib, in women with ER-positive, HER2-negative advanced breast cancer [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 P3-07-28.