Treatment Of Metastatic Breast Cancer Research Articles

Vitreoretinal Traction Syndrome, Nitrituria and Human Epidermal Growth Factor Receptor Negative Might Occur in the Aromatase-Inhibitor Anastrozole Treatment

Background. Anastrozole has been approved for treatment of hormone receptor-positive advanced or metastatic breast cancer by FDA. This study was to assess Anastrozole-related adverse events (AEs) of real-world through data mining of the US Food and drug administration adverse event reporting system (FAERS). Methods. Four different disproportionality analyses, including the reporting odds ratio (ROR), the proportional reporting ratio (PRR), the Bayesian confidence propagation neural network (BCPNN) and the multiitem gamma Poisson shrinker (MGPS) algorithms were employed to quantify the signals of Anastrozole-associated AEs. Results. A total 25 system organ class (SOCs) and 300 significant disproportionality Preferred Terms (PTs) were found in this study. The top 5 most significant SOCs were Eye disorders, renal and urinary disorders, respiratory, thoracic and mediastinal disorders, investigations, and cardiac disorders. Unexpected significant AEs was vitreoretinal traction syndrome (ROR = 1108.22, PRR = 1103.98, IC025 = 9.51, EBGM05 = 389.98), nitrituria (ROR = 3561.82, PRR = 3557.28, IC025 = 10.38, EBGM05 = 318.83) and human epidermal growth factor receptor negative (ROR = 675.04, PRR = 674.01, IC025 = 9, EBGM05 = 204.57). Conclusion. The Unexpected significant AEs associated with anastrozole were identified in this study, warrants urgent clarification through additional prospective studies.

Abemaciclib for the Treatment of HR+HER2− Metastatic Breast Cancer: An Institutional Experience

(1) Background: Abemaciclib combined with endocrine therapy is a standard first- or later--line of treatment for HR+/HER2− metastatic breast cancer (MBC). The aim of this retrospective cohort study was to describe the outcomes of patients treated in a real-world setting, with particular focus on elderly patients. (2) Patients and methods: Patients treated with abemaciclib between November 2019 and February 2022 were included in the study. Data were collected from electronic medical records. The primary objective was to determine real-world progression-free survival (rwPFS), and secondary objectives included median overall survival (mOS) and safety. (3) Results: Analysis included 134 patients, with a median follow-up of 42 months. Median age was 62 years, with 29.9% aged 70+ years. A total of 51.5% of patients received abemaciclib in first-line, predominantly with aromatase inhibitor (68.1%). Median rwPFS was 21 in first-line and 20 months in the second-line, with no significant difference between treatment lines (HR 0.96; p = 0.88). Patients treated in the third- or later-line had a significantly shorter rwPFS, at 7 months (HR 1.48, p = 0.003). mOS was not reached in the first-line setting. For second- and third- or later-lines, mOS was 29 and 19 months, respectively. There was no significant difference in mOS between first- or second-line (HR 1.37, p = 0.36). In the 70+ group, median rwPFS was 15 months and mOS was 25 months with no significant difference compared to younger patients (rwPFS HR 1.1; p = 0.65; OS HR 1.4; p = 0.21). Most common adverse events (AEs) were diarrhoea (68.7%), anaemia (64.9%), and increased serum creatinine (63.4%). Grade 3/4 AEs were reported in 21.6% of patients. Dose reductions occurred in 30.6% of patients and were more frequent in patients 70+ (40%) compared to younger patients (28%); the difference was not significant (p = 0.22). At study cut-off, 64.9% of patients discontinued abemaciclib, primarily due to disease progression (73.5%). (4) Conclusions: Our study provides valuable insights into the effectiveness and safety of abemaciclib for the treatment of MBC. We observed comparable outcomes in terms of rwPFS and OS between the first two lines, suggesting consistent effectiveness across treatment lines. In addition, our findings suggest that older age (70+) does not significantly impact the effectiveness and tolerability of abemaciclib, although the careful monitoring and management of AEs are warranted.

Iterative Development of an Interactive Website to Support Shared Decision-Making in Metastatic Breast Cancer.

Recent treatment advances have resulted in significantly increased survival times following metastatic breast cancer (MBC) diagnosis. Novel treatment approaches-and their related side effects-have changed the landscape of MBC treatment decision-making. We developed a prototype of an online educational tool to prepare patients with MBC for shared decision-making with their oncologists. We describe the five phases of tool development: (1) in-depth, semi-structured qualitative interviews and (2) feedback on storyboards of initial content with patients with MBC and oncology providers. This was followed by three phases of iterative feedback with patients in which they responded to (3) initial, non-navigable website content and (4) a beta version of the full website. In the final phase (5), patients newly diagnosed with MBC (N = 6) used the website prototype for 1week and completed surveys assessing acceptability, feasibility, treatment knowledge, preparation for decision-making, and self-efficacy for decision-making. Participants in Phase 1 characterized a cyclical process of MBC treatment decision-making and identified key information needs. Website content and structure was iteratively developed in Phases 2-4. Most participants in Phase 5 (n = 4) accessed the website 2-5 times. All participants who accessed the website at least once (n = 5) felt they learned new information from the website prototype and would recommend it to others newly-diagnosed with MBC. After using the website prototype, participants reported high preparation and self-efficacy for decision-making. This multiphase, iterative process resulted in a prototype intervention designed to support decision-making for MBC patients.

Mitomycin C in the treatment of early triple-negative locally advanced BRCA-associated breast cancer

Rationale. BRCA1 associated triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer. At the same time, carcinomas that develop in carriers of BRCA1 mutations are characterized by extremely high sensitivity to DNA-damaging chemotherapy. Mitomycin C alone or in combination with platinum agents has already demonstrated promising results in the treatment of BRCA-associated ovarian cancer (OC) and metastatic breast cancer. In this article, we present the results of a retrospective study aimed at comparing standard neoadjuvant chemotherapy regimens (NACT) with mitomycin-based regimens for primary locally advanced BRCA1-associated TNBC.The aim of the study is to determine the effectiveness of the combination of mitomycin and platinum compounds during neoadjuvant therapy in patients with primary locally advanced BRCA1 – associated TNBC.Materials and methods. The study included 89 patients diagnosed with primary locally advanced BRCA1-associated TNBC. Patients were divided into three groups depending on the therapy: 1) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel (n = 48) (AC + T), 2) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel and carboplatin (n = 27) (AC + TCbP), 3) mitomycin C plus platinum followed by 12 weekly injections of paclitaxel (n = 14) (MR + T). Pathological complete response (pCR) rates were compared.Results. The pCR rate in the MP+T group was 10/14 (71%). In patients with BRCA1-associated breast cancer who received AC + T and AC + TCbP regimens as NACT, the pCR rate was 17/48 (35%) and 19/27 (70%), respectively. The difference in pCR rate between mitomycin-containing therapy and the standard AC + T regimen was statistically significant (p = 0.03); the frequency of regressions was comparable to the frequency in the AC + TCbP group. During the 20-month follow-up period, no relapses were observed in the MR + T group. Relapses were more frequent in the AC + T group compared with the AC + TCbP group (16/48 (33%) vs 1/27 (4%), p = 0.003, Fisher’s exact test). The toxicity profile of the mitomycin-containing regimen included hematologic adverse events, the most common of which were anemia and leukopenia. Compared to standard regimens, nausea was significantly less pronounced. No patients reported alopecia with this regimen.Conclusions. The addition of mitomycin C to neoadjuvant therapy for BRCA1-associated TNBC may be a promising treatment option for this category of patients and merits further study.

Case report: Treatment with Phesgo® in a patient receiving hemodialysis

IntroductionPatients with metastatic HER2-positive breast cancer have multiple therapeutic options. However, most are not studied in the renal replacement therapy (RRT) setting.Case reportWe report the use of Phesgo® (subcutaneous fixed-dose combination of trastuzumab and pertuzumab) combined with exemestane as a first-line treatment of metastatic HER2-positive breast cancer in a hemodialysis patient with multiple comorbidities. Partial response was attained, with disease progression after 8 months without evidence of significant toxicity.DiscussionsThis case report is, to our knowledge, the first published case documenting the use of Phesgo® in a hemodialysis patient. No new safety signs were seen, and activity was documented, adding support to the use of this drug combination in such a patient population.

Racialized economic segregation and inequities in treatment initiation and survival among patients with metastatic breast cancer.

Racialized economic segregation, a form of structural racism, may drive persistent inequities among patients with breast cancer. We examined whether a composite area-level index of racialized economic segregation was associated with real-world treatment and survival in metastatic breast cancer (mBC). We conducted a retrospective cohort study among adult women with mBC using a US nationwide electronic health record-derived de-identified database (2011-2022). Population-weighted quintiles of the index of concentration at the extremes were estimated using census tract data. To identify inequities in time to treatment initiation (TTI) and overall survival (OS), we employed Kaplan-Meier methods and estimated hazard ratios (HR) adjusted for clinical factors. The cohort included 27,459 patients. Compared with patients from the most privileged areas, those from the least privileged areas were disproportionately Black (36.9% vs. 2.6%) or Latinx (13.2% vs. 2.6%) and increasingly diagnosed with de novo mBC (33.6% vs. 28.9%). Those from the least privileged areas had longer median TTI than those from the most privileged areas (38 vs 31days) and shorter median OS (29.7 vs 39.2months). Multivariable-adjusted HR indicated less timely treatment initiation (HR 0.87, 95% CI 0.83, 0.91, p < 0.01) and worse OS (HR 1.19, 95% CI 1.13, 1.25, p < 0.01) among those from the least privileged areas compared to the most privileged areas. Racialized economic segregation is a social determinant of health associated with treatment and survival inequities in mBC. Public investments directly addressing racialized economic segregation and other forms of structural racism are needed to reduce inequities in cancer care and outcomes.

Abstract PO1-05-13: Drop-out rates from line to line of treatment in metastatic breast cancer (MBC): Results from the Austrian AGMT_MBC-Registry

Abstract Background: In metastatic breast cancer (MBC) continuous treatment with sequentially administered cancer drugs is the standard of care. Lines of treatment (LoT) consisting of single drugs or drug combinations are usually administered until disease progression or unacceptable toxicity. To provide as many patients as possible access to the most effective therapies, the “best treatment first” strategy has been established as a subset of patients will be lost from LoT to LoT. To investigate drop-out rates in all subsequent LoT, high-quality real-world data are needed. Here, we present data from the Austrian Study Group of Medical Tumor Therapy (AGMT) MBC-Registry, a multicenter nationwide ongoing retrospective and prospective registry for MBC patients in Austria. Patients and methods: Patients with known hormone-receptor (HR) and HER2 status, available survival data and at least one LoT were included. Therapies administered between diagnosis or disease progression and subsequent disease progression were counted as one LoT. All types of antitumor drugs (endocrine therapy, targeted therapy, chemotherapy, immunotherapy) were considered. Results: As of 16-May-2023, 2,484 patients were included in the registry. Out of 2,044 evaluable patients, 1,330 (65.1%) were HR+/HER2-, 251 (12.3%) were HR+/HER2+, 146 (7.1%) were HR-/HER2+ and 317 (15.5%) were triple-negative, respectively. The median number of treatment-lines in the overall cohort was 3 (range 1-14; 95%CI 3-3). In patients with HR+/HER2-, HR+/HER2+, HR-/HER2+ and triple-negative tumors the median LoT were 3 (range 1-14; 95%CI 3-4), 4 (range 1-13; 95%CI 3-4), 3 (range 1-10; 95%CI 3-4) and 2 (range 1-9; 95%CI 2-3), respectively. Overall, 641 patients were still on treatment at data cut off. The estimated percentage of patients being treated in each LoT and the corresponding drop-out rates from 1st- to 5th-line are provided in Table 1. Conclusion: Relevant drop-out rates even in the early treatment lines support a “best treatment first” strategy. An accelerated investigation of promising cancer drugs in early treatment lines in patients with MBC is warranted. Drop-out-Rate 1st-line 2nd-line 3rd-line 4th-line 5th-line All n 2044 1281 869 558 344 Drop-out-Rate / 23.8% 24.8% 30.9% 34.0% HR+/HER2- n 1,330 854 586 380 244 Drop-out-Rate / 19.6% 23.0% 29.6% 30.7% HR+/HER2+ n 251 157 109 72 48 Drop-out-Rate / 23.4% 20.4% 25.0% 28.4% HR-/HER2+ n 146 78 59 37 24 Drop-out-Rate / 36.6% 16.9% 36.2% 33.3% Triple-negative n 317 192 115 69 28 Drop-out-Rate / 34.0% 38.2% 39.5% 57.6% Citation Format: Simon Gampenrieder, Gabriel Rinnerthaler, Angelika Pichler, Walter Herz, Andreas Petzer, Clemens Dormann, Marija Balic, Christoph Suppan, Sonja Heibl, Lukas Scagnetti, Margit Sandholzer, Clemens Schmitt, August Zabernigg, Daniel Egle, Petra Pichler, Christopher Hager, Florian Roitner, Johannes Andel, Kathrin Strasser-Weippl, Rupert Bartsch, Michael Hubalek, Michael Knauer, Christian F. Singer, Richard Greil. Drop-out rates from line to line of treatment in metastatic breast cancer (MBC): Results from the Austrian AGMT_MBC-Registry [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-05-13.

Abstract PO1-04-05: Effectiveness and safety of inetetamab + pyrotinib + vinorelbine in ≥second-line treatment of HER2-positive metastatic breast cancer

Abstract Background: In real-world settings, Patients with HER2-positive metastatic breast cancer (MBC) who cannot receive antibody-drug conjugates (ADCs) as standard second-line therapy due to cost–benefit ratios and who have no preferred options as ≥third-line regimen by NCCN guidelines, require new regimens to meet their clinical needs. This study aims to explore the effectiveness and safety of inetetamab + pyrotinib + vinorelbine for ≥second-line treatment of HER2-positive MBC. Methods: Patients with HER2-positive MBC who received ≥second-line treatment at our hospital from June 2020 to December 2022 were enrolled. Progression-free survival (PFS), objective response rate (ORR), clinical benefit rate (CBR) and adverse reactions were assessed. Patients received inetetamab + pyrotinib + vinorelbine until disease progression or unacceptable toxicity were evaluated every two cycles according to the RECIST 1.1 criteria. Results: 89 patients were included based on the inclusion and exclusion criteria. Among them, 45 patients received second-line treatment who couldn't use T-DM1 or T-DXd, and 44 patients received ≥third-line treatment. The median PFS of the second-line treatment subgroup was 17months, the ORR and CBR were 60.0% and 86.7%, respectively, which were significantly higher than those in the ≥third-line treatment subgroup and numerically superior to T-DM1 as a second-line treatment option. Additionally, the ORR and CBR of patients with baseline brain metastasis who did not receive radiotherapy were 27.3% and 72.7%, respectively. The most common adverse events observed were leukopenia (37.1%), neutropenia (42.7%), anemia (34.8%) and diarrhea (67.4%). The incidence of grade 3-4 leukopenia, neutropenia, anemia and diarrhea were 11.2%, 15.7%, 55.6% and 27.0%, respectively. A total of 8 patients (8.9%) discontinued medication due to adverse reactions. Conclusions: Inetetamab + pyrotinib + vinorelbine demonstrates good efficacy and controllable toxicity as a second-line treatment for HER2-positive MBC. This therapeutic regimen provides a viable alternative option for patients who are unable to receive ADCs as the second-line treatment. Citation Format: Fan Wu, Mulan Chen, Weiwei Huang, Lili Wang, Nani Li, Xiufeng Wu, Xinhua Chen, Yi Hong, Lin Lin, Kan Chen, Jian liu. Effectiveness and safety of inetetamab + pyrotinib + vinorelbine in ≥second-line treatment of HER2-positive metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-04-05.

Abstract PO4-04-07: Efficacy, safety and translational study of pyrotinib combined with albumin-bound paclitaxel as firstline treatment of HER-2 positive metastatic breast cancer

Abstract Objective: Breast Cancer is one of the most common malignant tumors in women. HER-2 is a driver gene for poor prognosis in breast cancer. Anti-HER-2 drugs have significantly improved the prognosis of patients with HER-2 positive metastatic breast cancer. There is still a lack of exploration of first-line anti-HER2 treatment options and translational studies only for patients with metastases after adjuvant and/or neoadjuvant trastuzumab therapy. This study is based on our previous clinical trial of pyrotinib in combination with albumin-bound paclitaxel in first line for patients with HER-2-positive metastatic breast cancer after adjuvant and/or neoadjuvant trastuzumab therapy, with the aim of exploring the efficacy and adverse events in the enrolled patients. And to explore the markers associated with Progression Free Survival (PFS) by using Olink technique to detect blood samples from patients. To provide a better screening of the benefit population and provide guidance for the treatment of HER-2 positive metastatic breast cancer. Methods: From December 2019 to July 2023, our previous clinical trial prospectively enrolls 27 patients with HER-2-positive metastatic breast cancer after adjuvant and/or neoadjuvant trastuzumab therapy. Pyrotinib (400 mg, po, qd) combined with albumin-bound paclitaxel (200 mg, ivdrip, d1, d8, q21d) was used as the first-line treatment regimen. Patients were evaluated for efficacy. Survival analysis was performed by using the Kaplan-Meier method. Blood samples were collected during treatment. We selected 21 blood samples from patients, and dynamically detected plasma protein changes by Olink technique. Differential protein analysis between groups according to hormone receptor status, trastuzumab primary/secondary resistance, and the presence of visceral metastases. And the proteins associated with PFS were analyzed. Results: Among the 27 patients whose efficacy had been evaluated, 7 patients were evaluated as CR, 18 patients as PR, and 2 patients as SD. The objective response rate was 92.6%, and the disease control rate was 100%. The median follow-up was 17.8 months and the median PFS has not yet been reached. Diarrhea is the most common adverse event. Grade 3 or higher adverse events include diarrhea, leukocytopenia, neutropenia, and hand-foot syndrome. The progression free survival was significantly worse in patients with visceral metastases (P=0.01). Results of Olink protein dynamic assay showed a significant downregulation of CEACAM5, TXLNA, PVRL4and ERBB2. Differential proteins between groups showed that there were no significant differential proteins between the hormone receptor-positive and negative groups at the baseline node, but 7 proteins were upregulated in the hormone receptor-positive group compared with the negative group at the progression node, with EMS-1, WIF-1, and hK14 being the most significant. Compared to primary resistance, trastuzumab secondary resistance appeared 4 proteins upregulated at the baseline node, with hK14 and CYR61 being the most significantly; and 33 proteins were upregulated at the progression node, with CYR61, CXL17, FURIN, and ABL1 being the most significantly. Patients with high expression of TLR3 and low expression of RET at the baseline node had longer PFS. Conclusions: This study demonstrates that pyrotinib in combination with albumin-bound paclitaxel as a first-line treatment regimen shows good efficacy and a manageable safety for patients with HER-2-positive metastatic breast cancer after adjuvant and/or neoadjuvant trastuzumab therapy. PFS was shorter in patients with visceral metastases. TLR3 and RET were the proteins that significantly associated with PFS in patients. Citation Format: Huihui Li, Xiaochu Man, Sha Yin, Dongdong Zhou, Baoxuan Zhang, Shu Fang, Fangchao Zheng, Chao Li, Xinzhao Wang, Wei Huang, Linlin Wang, Qingqing He, Hui Fu, Yan Zhang, Changrui Liu, Lin Dong, Xianguang Zhao, Liang Xu, Xiao Sun, Bingjie Fan, Lihua Song, Zhengbo Zhou, Qiaorui Tan, Jinming Yu. Efficacy, safety and translational study of pyrotinib combined with albumin-bound paclitaxel as firstline treatment of HER-2 positive metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-04-07.

Abstract PO1-18-01: Patient Preferences for HR+/HER2- Metastatic Breast Cancer Treatments in Italy: A Qualitative Assessment

Abstract Objectives: Factors that influence treatment preferences of patients with hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (mBC) are being investigated using discrete choice experiment (DCE) methodology. Appropriate attributes for the ongoing quantitative online survey phase were identified by this initial qualitative pilot study. Methods: To generate hypotheses and inform variables of the quantitative survey, the pilot phase consisted in online telephone interviews with patients with a diagnosis of Stage IV HR+/HER2- breast cancer at various stages of treatment. Interviews focused on exploring patients' perspectives on their interaction with physicians, preferences, and treatment experiences. Transcripts were coded using NVivo software to identify key themes. The ongoing DCE online survey aims to recruit patients meeting the same selection criteria as in the qualitative phase, also at various stages of treatment. Results: Fifteen mBC patients (median age, 43 years [range, 29-64]), including nine chemotherapy-treated and six without chemotherapy exposure, were enrolled in the pilot qualitative study. Eight and four patients reported receiving little information about their treatment plan and their risk status beyond the risk of relapse, respectively. Most participants did not know what to expect from their therapy but expressed trust in their physician’s decision in terms of treatment goals. Few patients (n=3) looked for a second opinion before starting treatment. Four out of fifteen patients declared that they were actively involved in their treatment plan decision, although all relied on their physician’s knowledge and decision. Reduced symptoms and improved quality of life (QoL) were patients’ main treatment goals, and side-effects and efficacy of treatment were their main concerns. When asked about the degree of acceptability of certain side effects, some participants considered hair loss and vomiting as unacceptable side effects, regardless of severity, while others considered them to be the most acceptable. This discrepancy is to be interpreted in the light of participants’ own treatment journey. Severity and duration of side-effects were mentioned by three patients as acceptability factors. In a choice task, patients were asked to express preferences between two hypothetical treatments. Efficacy (n=9) and administration mode (n=6) were spontaneously deemed important for treatment selection. While assessing the difference in risk between the two hypothetical treatments, ten patients explained that the main choice feature was extended progression-free survival (PFS) rate. Risk of infection and neutropenia (n=12) were concerns expressed by most patients in the post-COVID-19 period. Considering their substantial impact on QoL, alopecia (n=9) and vomiting (n=9) were presented by patients as particularly important, regardless of their degree of severity; whereas almost all patients reported that only severe fatigue (n=12), diarrhea (n=13) or nausea (n=13) would be an issue. These results allowed selection of the following attributes for further quantification of their preference weights in a DCE: PFS, risk of neutropenia, risk of alopecia, risk of vomiting, risk of diarrhea, risk of grade 3/4 side effects and mode of administration. Conclusions: This qualitative pilot study allowed for identification of what matters most to patients when selecting a treatment for mBC, which will be further assessed in the DCE. It also highlighted the need of patients with HR+/HER2- mBC for information about their treatment, potential side-effects, and health management. This research suggests that there is a need for patients to be more involved in treatment plans, and that taking patient preferences into account may help improve the treatment selection experiences. Citation Format: Grazia Arpino, Carmine De Angelis, Lorenzo Gerratana, Matteo Lambertini, Sarah Igidbashian, Martina Bellini, Serena Giuntoli, Xavier Guillaume, Julie Behillil, Claire Graziani-Taugeron. Patient Preferences for HR+/HER2- Metastatic Breast Cancer Treatments in Italy: A Qualitative Assessment [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-18-01.

Abstract PO4-04-04: A Multicenter, Retrospective, Real World Study of Inetetamab Combined with Pyrotinib and Vinorelbine as Treatment for HER2-positive Metastatic Breast Cancer

Abstract Background Inetetamab, a new human epidermal growth factor receptor 2 (HER2) targeted antibody to optimize the ADCC effect, has shown great effectiveness in treating HER2-positive metastatic breast cancer. Pyrotinib, another HER2 targeted drug, is a typical representative of TKI drugs, which not only has a strong HER2 antagonistic effect but also can synergize with monoclonal antibodies to amplify the ADCC effect. Here, we investigated the efficacy and safety of inetetamb combined with pyrotinib and vinorelbine as treatment or HER2-positive metastatic breast cancer. Methods From Jan 2020 to July 2023, 77 HER2-positive metastatic breast cancer patients received inetetamb combined with pyrotinib and vinorelbine were enrolled in this study. Progression-free survival (PFS), overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR), and safety profiles were reported. Results The patients’ median age at enrollment was 53 years, 35 patients (45.5%) had hormone receptor-positive disease and 54 patients (70.1%) had visceral metastasis. The median PFS was 10.03 months (95% confidence interval [CI] 6.66 to 13.41 months). ORR was 62.3% (48/77) and CBR reached 77.9% (60/77). The most common adverse event (AE) was diarrhea, occurring in 36 patients (46.8%). While the most common grade III/IV AEs included neutropenia (9[11.7%]), leukopenia (8[10.4%]) and diarrhea (5[6.5%]). No treatment-related serious adverse events or treatment-related deaths occurred. Conclusion The combination regimen of inetetamab combined with pyrotinib and vinorelbine showed an encouraging efficacy and favorable safety in patients with HER2 positive metastatic breast cancer. Citation Format: Yongmei Yin, Wei Li, Xiang Huang, Nan Jin, Xinyu Wu, Chunxiao Sun, Yijia Hua. A Multicenter, Retrospective, Real World Study of Inetetamab Combined with Pyrotinib and Vinorelbine as Treatment for HER2-positive Metastatic Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-04-04.

Abstract PO4-14-06: Impact of Serum HER2 Extracellular Domain in Metastatic Breast Cancer Patients Treated with Trastuzumab Deruxtecan (T-DXd)

Abstract Background: Trastuzumab deruxtecan (T-DXd) is a standard of care as 2nd line and after prior chemotherapy for HER2 positive and low metastatic breast cancer (MBC), respectively, based on Destiny Breast03 and 04 results. However, biopsies over time during treatment have shown that HER2 expression is variable. The predictive factors of trastuzumab deruxtecan (T-DXd) for MBC with HER2 positive and low are unclear. The HER2 extracellular domain (HER2-ECD) has been confirmed as a prognosis marker and predictive marker of treatment for HER2-positive MBC. Especially, HER2-ECD is considered a promising biomarker in cases where HER2 expression in metastases is unconfirmed. We hypothesized that HER2-ECD could serve as a biomarker for T-DXd. Patients and methods: A retrospective study of consecutively treated patients in a single center between 2019-2023 with HER2-low and HER2-positive MBC was performed using chart review. HER2 status was diagnosed according to 2020 ASCO-CAP guidelines. HER2-ECD high was defined as &amp;gt;15.0 ng/ml. HER2-ECD was collected prior to T-DXd treatment. We compared overall response (ORR), progression-free survival (OFS), overall survival (OS), and disease control rate (DCR) at HER2-ECD high and low groups. Cox regression analyses were performed to assess the ORR. We used the Kaplan-Meier method to estimate the PFS and OS and the log-rank test to compare each treatment group. Results: A total of 41 MBC patients were included in this study. Patients with HER-positive and HER2-low were 34 and 7, respectively. Among HER2 positive (n=34), HER2-ECD high and low are 14 (41%) and 20 (59%) patients, respectively. Among HER2 low (n=7), HER2-ECD high and low are 3 (43%) and 4 (57%) patients, respectively. Twenty-six patients received T-DM1 prior to T-DXd treatment for MBC with HER2 positive, but no patients received CPT-11 before T-DXd for MBC with HER2 positive and low. The ORR of T-DXd was 89% and 52% in the HER2-ECD high and low groups, respectively (p&amp;lt; 0.001). All 6 cases with CR were HER2-ECD high. Among HER2 low group (n=7), ORR of T-DXd was 67% (2/3) and 25% (1/4) in HER2-ECD high and low groups, respectively. The median PFS in the HER2-ECD high group showed longer than the HER2-ECD low group, 21.8 vs. 8.0 months (HR 0.31; 95%CI, 0.13-0.78, p=0.012). Although there were no significant differences in OS, HER2 ECD high group tended to show longer OS (HR 0.23; 95%CI, 0.04-1.16, p=0.07). The DCR was 100% in the HER2 ECD high group and 87% in the low group. Conclusion: T-DXd showed significantly better response and prolonged PFS in the group with high HER2-ECD. HER2-ECD has the potential to become a biomarker for T-DXd. Further study is warranted to assess the HER2-ECD as a biomarker, especially for HER2 low MBC patients treated with T-DXd. Table. Association between the response and the HER2 status or HER2-ECD status Citation Format: Kazuki Nozawa, Maho Kusudo, Nari Kureyama, Akira Nakakami, Rie Komaki, Yuka Endo, Ayumi Kataoka, Haruru Kotani, Akiyo Yoshimura, Masaya Hattori, Masataka Sawaki, Hiroji Iwata. Impact of Serum HER2 Extracellular Domain in Metastatic Breast Cancer Patients Treated with Trastuzumab Deruxtecan (T-DXd) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-14-06.

Abstract PO4-05-01: Clinical outcomes of breast cancer and its relationship with access to health care in Brazil: prospective study in HER2 negative/hormone receptor positive metastatic disease - BREAST (BRazilian outcomE for metAStatic breasT cancer)

Abstract Background: Cancer survival is one of the key measures of the effectiveness of cancer services and captures whether people have access to effective treatment. The survival rate of breast cancer in low and middle-income countries is notably different from high-income countries; this disparity in survival reflects limited access to first-line systemic therapy for advanced and metastatic tumors. Recent studies have shown benefit of combining cyclin-dependent kinase 4 and 6 inhibitors (CDK 4/6) with endocrine therapies in hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced or metastatic breast cancer. However, in Brazil, the population has limited access to these drugs, mainly in the public health service. The commercialization of CDK 4/6 inhibitors was only released in the national territory in 2018, but until nowadays it is not accessible for most patients. Objective: The aim of this project is to assess whether patients without private health insurance may experience worse outcomes compared to women with private insurance, primarily due to limited access to a specific class of medication during their treatments. The study seeks to gain insights into the clinical outcomes of patients with HR+ HER2- metastatic breast cancer based on their access to health insurance coverage within a real-world setting. Methods: Multicenter, prospective observational study, with patients divided into two groups: one with patients from the public health system and the second with patients treated at the private service. Whereas that the hazard ratio for the primary outcome in the private system compared to the public health system is like that observed in the PALOMA study (0.58), and that event rates after 18 months of follow-up are also similar (approximately 45% and 35%), then a total of 298 patients will provide the study power of 80%, significance level of 5%. This calculation considers a sample size ratio of 1 patient in the private health system for every 2 patients in the public health system. The inclusion criteria specify women with HR+ HER2- metastatic breast cancer who initiated first-line treatment from 2019. Patients will be followed for 24 months and stratified based on the use or non-use of CDK 4/6 inhibitors. The study was approved by the local ethics committee and registered with Clinical Trials (NCT05559528). Results: A total of 300 patients were evaluated, with 199 (66.3%) in the public health system and 101 (33.7%) in the private service. The mean age was 58 years, and 76.2% were postmenopausal. In terms of metastasis site, 84.7% had non-visceral disease, predominantly with bone metastasis (75.7%), which is an expected characteristic of this type of tumor. The use of CDK 4/6 inhibitors at any point in the treatment of metastatic disease was 7.0% in the public health system versus 90.1% in the private service. As a preliminary outcome, with a median time since the diagnosis of metastatic breast cancer of 22.8 months, a mortality rate of 10% was identified in the public health system group compared to 5% in the private service group. Conclusions: The results of our study highlight the disparity in the treatment of metastatic breast cancer among patients in relation to access to healthcare. Patients dependent on the public health system experience higher mortality rates. These findings are crucial for supporting discussions on improving local policies regarding access to medications that have been proven to enhance the prognosis of these patients. Citation Format: Vanessa Sanvido, Lucíola Pontes, Rachel Machado, Marina Nicola, Jackeline Gomes, Letícia Barbante, Nanci Valeis, Alexandre Cavalcanti, Afonso Nazário. Clinical outcomes of breast cancer and its relationship with access to health care in Brazil: prospective study in HER2 negative/hormone receptor positive metastatic disease - BREAST (BRazilian outcomE for metAStatic breasT cancer) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-01.

Abstract PO2-05-14: Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort

Abstract Background: HER2-negative breast cancers expressing low (1-9 %) immunohistochemistry levels of hormone receptors (HR, estrogen and progesterone receptors), remain an uncertain category, being considered either as triple negative breast cancers (TNBC) or HR-positive (HR+) tumors across guidelines or approvals. The issues regarding this clinical subgroup are both prognostic, with the need of a better definition of their clinical outcome, as well as predictive. Methods: The ESME database is a French National cohort of all consecutive patients who initiated a first-line treatment for metastatic breast cancer (MBC) from 2008 on, in one of the 18 French Comprehensive Cancer Centers. Patients with HER2-negative (0 to 2+, ISH negative) MBC and known estrogen receptor (ER) and progesterone receptors (PR) expression levels were selected. Primary objective was to evaluate crude overall survival (OS) in HER2-/HR-low (ER and PR 0-9 and not TNBC) MBC pts compared with those with TNBC and HR+ disease defined by ER and PR &amp;lt; 1%, and ER ± PR ≥ 10%, respectively. In these 3 populations, predefined secondary objectives were to evaluate PFS under first line chemotherapy (CT), to describe clinical characteristics and the distribution of genetic abnormalities identified at the time of MBC diagnosis. Results: Out of 30,459 patients in the ESME database initiating their MBC treatment between 01/2008 and 01/2021, 19109 patients (2113 TNBC; 228 HR-low; 16768 HR+) were eligible for this analysis. Median follow-up was 58.0 months (95%CI [56.6; 59.0]). Median OS were 15.7 months [15.0-16.8], 19.1 months [15.5-22.4] and 44.6 months [43.8-45.5] in the TNBC, HR-low and HR+ subgroups, respectively. The multivariable analysis adjusted on age at MBC diagnosis, pathological grade and subtype, metastatic-free interval, number and sites of metastases and HER2 status (0 vs. 1-2+), identified no significant OS difference between HR-low and TNBC subgroups (HR=0.95, 95%CI 0.79-1.14), while HR+ patients had a better OS than TNBC patients (reference) (HR=0.50, 95%CI 0.47-0.53). Of these 19109 pts, 8910 received first-line CT regimen (1960 TNBC; 195 HR-low; 6755 HR+): taxanes-based: 66.7%, anthracyclines-based: 32.9%, capecitabine: 18%. Median PFS under first line CT were 5.3 (5.1-5.6), 5.1 (4.1-6.2) and 10.2 months (9.9-10.6) for TNBC, HR-low and HR+ subgroups, respectively. In the multivariable analysis adjusted on the same variables, the HR-low subgroup had a statistically poorer PFS compared to TNBC (HR=1.24, 95% CI 1.04-1.49). On the other hand, the HR+ subgroup had a better PFS than the TNBC (HR=0.74, 95%CI [0.70; 0.78]). Baseline germline BRCA1 mutations (at MBC diagnosis) were present in 4.5% of the TNBC cases, 2.6% of the HR-low cases, and 0.4% of the HR+ cases. The distribution of germline BRCA2 mutations was more homogeneous between the three groups (0.9% of TNBC cases, 1.3% of HR-low cases and 1.1 % of HR+ cases). Conclusions: In this large cohort, patients with HER2-negative, HR-low MBC seem to share similar general prognosis, oncogenetic features and PFS under standard chemotherapy treatment with TNBC patients. Citation Format: Marie Alexandre, Ludovic Gauthier, Audrey Mailliez, Thibault DE LA MOTTE ROUGE, Thomas Bachelot, Monica Arnedos, Florence Dalenc, Etienne Brain, Jean-Marc Ferrero, Vincent Massard, Isabelle Desmoulins, Marie-Ange Mouret-Reynier, Christelle Levy, Anthony Gonçalves, Marianne Leheurteur, Thierry Petit, Jean-Sébastien Frenel, Lise Bosquet, Suzette Delaloge, William Jacot. Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-14.

Abstract PO4-06-12: Distinction of basal-like and triple-negative basal-like breast cancers utilizing a novel comprehensive single-cell liquid biopsy-based test

Abstract Introduction: Breast cancer is a highly heterogeneous disease and is a leading cause of death for women worldwide. Triple-negative breast cancer (TNBC), the most aggressive form of the disease, is clinically defined by the lack of expression of estrogen receptor (ER) and progesterone receptor (PR), as well as lack of over-expression of human epidermal growth factor receptor-2 (HER2). Approximately 70% of all TNBC cases exhibit basal-like cells, characterized by high basal expression of keratins as well as extensive genomic instability with copy number gains and losses across most chromosomes. In this study we show that novel single cell genomic evaluation coupled with immunofluorescence (IF) protein analysis of CTCs can detect TNBC with basal-like genomic features as well as basal-like tumors with expression of ER and HER2. Materials and Methods: Epic Sciences’ DefineMBC™ liquid biopsy test characterizes CTC proteomics and genomics as well as ctDNA for the treatment of metastatic breast cancer. Blood samples from 813 metastatic breast cancer patients, with either newly diagnosed or progressing disease, with historical tissue subtype [HR(+)HER2(-), HR(+/-)HER2(+), and TNBC] supplied by the referring physician were collected and tested. Up to 5 CTCs were selected and isolated from each sample based on morphology and IF signal. DNA was extracted from individual cells, and whole genome amplified and sequenced at low coverage. Copy number analysis was performed to determine copy number gains and losses across chromosomes, as well as large scale-state transitions (LSTs) and ERBB2 amplification. CTCs characterized with high chromosomal instability (e.g., exhibiting &amp;gt;30 LSTs; 1Q firestorm and 8Q stair step) and high levels of cytokeratin expression (mean fluorescence intensity signal &amp;gt;10K) were categorized as basal-like. Results: By previous metastatic tissue biopsy, 77% were HR(+), 8% were HER2(+), and 12% were TNBC. CTCs categorized in DefineMBC as basal-like subtype (9.8 % of all samples tested) showed to be highly present in patients called as TNBC (79% basal-like). Additionally, 54% of HR(+) and 23% of HER2(+) had basal-like CTCS. Patients characterized with TNBC by metastatic tissue biopsy and by DefineMBC exhibited basal-like cells in 88% of the cases. Conclusion: The results show a novel clinical assay which utilizes CTC protein detection as well as single-cell genomic analysis to identify tumors driven by basal-like cells. Generally, TNBC is classified with negative biomarker expression. We show that CTCs in TNBC display genomically basal-like cells. CTCs from HR(+) and HER2(+) tumors may express basal-like features with preserved ER and HER2 expression. The comprehensive nature of DefineMBC™ utilizing genomic analysis of detected CTCs has provided a new tool to diagnose both basal-like TNBC and basal-like hormone receptor positive and HER2 over-expressing tumors. Citation Format: Alessandra Cunsolo, David Bourdon, Ernest Lam, Giuseppe Di Caro, Nilesh Dharajiya, Timothy Pluard, Lee Schwartzberg. Distinction of basal-like and triple-negative basal-like breast cancers utilizing a novel comprehensive single-cell liquid biopsy-based test [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-06-12.

Abstract PO2-05-12: Retrospective analysis on therapeutic efficacy and predictive indicators of eribulin plus anti-angiogenic drugs for metastatic breast cancer

Abstract Background: Eribulin has been widely used for the treatment of metastatic breast cancer (MBC). It has been found that eribulin can work in synergy with Bevacizumab or Anlotinib to achieve anti-angiogenic effects and possible synergistic enhancement. To optimize the efficacy of eribulin usage in late-line MBC patients, it is essential to delve deeper into the effects of combined treatments and gather more real-world clinical outcomes. Therefore, we evaluated the efficacy and safety of eribulin plus the anti-angiogenic drugs in late-line MBC patients. Objective: This study aims to retrospectively analyze the therapeutic efficacy and safety of eribulin plus anti-angiogenic drugs in treating metastatic breast cancer and explore predictive indicators of the therapeutic efficacy of eribulin in treating MBC. Methods: A retrospective review study was performed. 40 Patients diagnosed with MBC and treated with eribulin in Xi’an international medical center hospital from May 2020 to May 2021 were enrolled in this study. Patients were evaluable for this study and divided into two groups based on whether they received eribulin monotherapy or combined therapy. 22 patients were treated with eribulin monotherapy, and 18 were treated with eribulin and anti-angiogenic drugs (Bevacizumab and Anlotinib). Patients’ treatment parameters and characteristics were recorded. The Kaplan-Meier method was used to calculate the median PFS and corresponding 95% confidence interval (CI), and the Cox regression model was used for multivariate analysis of predictive indicators. The Fisher exact probability test was used to compare the difference in adverse reactions between the two groups, with a level of significance set at p-value &amp;lt; 0.05. Results: All study patients have an average of 5 treatment lines and a median progression-free survival (mPFS) of 4.2 months. The eribulin plus anti-angiogenic drug treatment group had a significantly prolonged mPFS compared to the group without anti-angiogenic drug treatment (7.0 months vs 2.0 months, p &amp;lt; 0.001, log-rank). Multivariate analysis identified that the combination of anti-angiogenic therapy (HR = 0.043, p = 0.004) and the occurrence of grade 3-4 neutropenia after treatment were two predictive factors for longer PFS (HR = 0.322, p = 0.009). In contrast, prior resistance to taxanes was predictive of shorter PFS (HR = 4.583, p = 0.019). Other factors, including age, Eastern Cooperative Oncology Group (ECOG) performance status, hormone receptor (HR) type, expression status, human epidermal growth factor receptor-2 (HER-2) expression status, Ki-67 level, number of metastatic lesions, and number of prior lines of Eribulin therapy, were not significantly associated with PFS. The results of Fisher’s exact test show that there was no significant increase in treatment-related adverse events (all grades) after combination with anti-angiogenic drugs. Conclusion: A combination of eribulin and anti-angiogenic therapy has significantly prolonged mPFS in the treatment of MBC patients. Other factors such as prior non-taxane resistance, grade 3-4 neutropenia occurrence after treatment, and combined anti-angiogenic therapy can be used as biomarkers for predicting treatment efficacy. The adverse events are manageable and the safety of combined therapy can be guaranteed. Therefore, the eribulin plus anti-angiogenic combination may act as a potential therapy for late-line MBC patients with clinically beneficial therapeutic effects. Keywords: metastatic breast cancer, eribulin, anti-angiogenic therapy, retrospective analysis Citation Format: Junmei Zhang, Xuezheng Wang, Hongjuan Du, Yan Xue. Retrospective analysis on therapeutic efficacy and predictive indicators of eribulin plus anti-angiogenic drugs for metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-12.

Abstract PO1-17-12: The impact of treatment sequence of CDK4/6 inhibitor therapy on Metastatic Breast Cancer treatment outcomes in Real-World practice in U.S

Abstract Background A retrospective study to describe the actual benefit of treatment sequence with Endocrine Therapy (ET) plus cyclin D/cyclin-dependent kinases 4 and 6 (CDK4/6) therapy including as 1st-line and 2nd -line treatment for Metastatic breast cancer (MBC) patients with hormone receptor positive (HR+) and HER2 negative. We examined the extent that treatment sequence of CDK4/6 inhibitor therapy is associated with progression-free survival, and overall survival under real-world conditions. Methods This study used the nationwide electronic health record-derived-Flatiron Health de-identified database to estimate the real-world progression-free survival (rwPFS) and overall survival (rwOS) of MBC patients under different treatment sequence of CDK4/6 inhibitors. A total of 2,771 patients with ≥ 3 months of follow-up received either CDK4/6 inhibitor plus ET in the first-line setting (n=2,170) or ET alone in the first-line and CDK4/6 inhibitor plus ET in the second-line setting (n=601) between February 3, 2015, and November 02, 2021. We performed inverse probability weighting (IPW) to balance the baseline demographic and clinical characteristics between patients in the two groups. Kaplan-Meier method and Cox proportional hazards were used to test for an association of CDK4/6 treatment line sequence on PFS as the primary outcome and OS as the secondary outcome, adjusting for patient characteristics (e.g., age, race, comorbidities, ECOG value, Tumor site, and health insurance). Results Median follow-up was 25.6 months (interquartile range [IQR], 12.7–41.3) for the group with CDK4/6 inhibitor plus ET in first-line treatment and 33.1 months (IQR, 18.1–50.4) in those taking ET alone in first-line and CDK4/6 inhibitor plus ET in the second-line treatment. CDK4/6 inhibitor combination with ET as the first-line treatment was associated with significantly longer median rwPFS compared to receiving ET alone on first line and CDK4/6 inhibitor plus ET in the second line (28.0 vs 13.1 months; hazard ratio [HR], 0.40; 95% CI, 0.35–0.44; P &amp;lt; 0.0001). Median rwOS was 52 months for the group with first line CDK4/6 inhibitor plus ET and 48 months for the other group who received CDK4/6 inhibitor in the second line of treatment. However, the difference was not statistically significant (HR=0.91, 95% CI, 0.78–1.09, P-value=0.33). A propensity scores matching analysis showed similar results. Conclusions In this “real-world” population of patients with HR+/HER2− MBC, receiving CDK4/6 inhibitor plus ET as first line of treatment was associated with improved progression free survival compared with patients treated with ET alone in the first-line and CDK4/6 inhibitor plus ET on the second line of treatment. Citation Format: Gretchen Kimmick, Asal PIlehvari, Wen You, Gloribel Bonilla, Roger Anderson. The impact of treatment sequence of CDK4/6 inhibitor therapy on Metastatic Breast Cancer treatment outcomes in Real-World practice in U.S [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-17-12.

Abstract RF02-05: Report on Cohort Expansion of Phase I Study to Investigate the Safety, Tolerability, Pharmacokinetics and Antitumor Activity of BB-1701 in Patients with Locally Advanced/Metastatic HER2 Low Breast Cancer

Abstract Background: BB-1701 is an antibody-drug conjugate (ADC) consisting of a humanized IgG1κ monoclonal anti-HER2 antibody with the same sequence as trastuzumab and eribulin linked together by a cathepsin-cleavable valine-citrulline linker. Eribulin is an inhibitor of microtubule approved for the treatment of metastatic breast cancer and advanced liposarcoma, following prior therapies. When BB-1701 targets HER2 expressing cancer cells and it is internalized, free eribulin is cleaved from the ADC by cathepsin b and causes cytotoxicity to cancer cells. The neighboring cells were affected with bystander effects, like cytotoxicity on tumor cells and non-cytotoxic effects on microenvironment, by free eribulin released from dying cancer cells. Here, we report preliminary results from the ongoing cohort expansion of a phase I study of BB-1701 in patients with HER2 low breast cancer (ClinicalTrials.gov Identifier: NCT 04257110). Methods: Patients ≥ 18 years of age with confirmed locally advanced/metastatic HER2 low breast cancer (IHC 2+ and FISH negative or IHC 1+), that had progressed on at least two lines of prior standard therapies, with ECOG PS ≤ 2 and measurable disease (RECIST 1.1) were enrolled. HER2 expressions was determined by IHC and FISH before enrollment. Total of four dose levels of BB-1701 (1.0 mg/kg Q3W, 1.2 mg/kg Q3W, 1.4 mg/kg Q3W and 1.6 mg/kg Q3W) were administered during the cohort expansion. The safety, tolerability and preliminary anti-tumor activity of BB-1701 were assessed during study. Radiographic assessment was conducted every 6 weeks. Results: As of 30 June 2023, 40 patients with HER2 low breast cancer were enrolled in the four dose levels, 5 patients at 1.0 mg/kg Q3W, 20 patients at 1.2 mg/kg Q3W, 5 patients at 1.4 mg/kg Q3W and 10 patients at 1.6 mg/kg Q3W. Median age was 55 years (range 30-74), 97.5% were female, and 30.0%/70.0% patients were ECOG PS 0/1. The median prior lines of systemic therapy were 3 (range 2 – 9). All subjects experienced at least one treatment emergent adverse events and treatment-related adverse events (TRAEs) occurred in 30 subjects. The most common all grade TRAEs (≥20%) were peripheral neuropathy, aspartate aminotransferase increased, alanine aminotransferase increased, anemia, white blood cell count decreased. Grade 3 TRAEs were peripheral neuropathy (3 subjects), peripheral sensory neuropathy (2 subjects), neutrophil count decreased (2 subjects), platelet count decreased (1 subject), white blood cell count decreased (1 subject). There were no grade 4 or grade 5 events. The treatment related serious adverse events (SAEs) were peripheral sensory neuropathy (1 subject) and infusion related reaction (1 subject). There was no interstitial lung disease reported. No patients discontinued the study treatment due to AE. Of the 40 patients enrolled, 38 patients were evaluable for antitumor activity. At 1.0 mg/kg dose level, of 5 patients treated, 2 achieved partial response (PR), 2 had stable disease (SD), best overall response rate (BOR) was 40.0% (2/5) and disease control rate (DCR) was 80.0% (4/5). At 1.2 mg/kg dose level, of 18 patients treated, 5 achieved PR, 11 had SD with BOR of 27.8% (5/18) and DCR of 88.9% (16/18). At 1.4 mg/kg dose level, of 5 patients treated, 2 achieved PR, 2 had SD with BOR of 40.0% (2/5), and DCR was 80.0% (4/5). One patient who achieved PR was previously progressed on sacituzumab govitecan. At 1.6 mg/kg dose level, of 10 patients treated, 1 achieved CR, 3 achieved PR, 2 had SD with BOR of 40.0% (4/10), and DCR of 60.0% (6/10). Among these patients, the patient who achieved CR was previously treated by disitamab vedotin, and one patient who achieved PR was previously treated by trastuzumab deruxtecan. Conclusions: BB-1701 has demonstrated promising preliminary antitumor activity in HER2 low breast cancer including patients who received prior anti-HER2 ADCs, and a manageable safety profile. Citation Format: Fei Ma, Pamela Munster, Xiaoxiang Guan, Jingfen Wang, Herui Yao, Erika Hamilton, Xian Wang, Yehui Shi, Xinjun Liang, Nong Xu, Huoling Tang, Yuhong Zhou, Ziping Wei. Report on Cohort Expansion of Phase I Study to Investigate the Safety, Tolerability, Pharmacokinetics and Antitumor Activity of BB-1701 in Patients with Locally Advanced/Metastatic HER2 Low Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr RF02-05.

Abstract PO1-11-02: Reporting of Post-protocol Therapies in Metastatic Breast Cancer Registration Clinical Trials: A Systematic Review

Abstract BACKGROUND As the treatment for metastatic breast cancer (MBC) often includes sequential lines of therapy, data on post-protocol treatment in clinical trials are valuable in the assessment of long-term outcome. The objective of this study was to assess the reported data on post-protocol therapy in clinical trials supporting US Food and Drug Administration (FDA) approval of drugs for MBC. METHODS We identified all initial and subsequent published trials supporting FDA approved indications for MBC between 1/2000-2/2023. Collected data included study design, patient characteristics and whether reporting on post-protocol therapy was available. Differences in study design and population between studies with and without data on post-protocol therapy were evaluated. FINDINGS A total of 41 indications for MBC were identified. Supporting studies comprised 20,152 patients. Data were evaluated from 241 publications or abstracts. Reporting of post progression therapy was available for 21 (51%) indications. Of these, post-progression therapy data were often partial and the appropriateness of the therapy could not be evaluated. At the time of FDA approval, data on overall survival (OS) were reported only in 17 (41%) studies. Of these, in 8 studies OS was significantly improved, in 7 studies OS was not improved and 2 studies were single arm. Differences between studies with and without data on post progression therapy are presented in the Table. Studies with OS as their primary endpoints were associated with significantly higher reporting of post-protocol therapy, while studies with both OS and progression free survival (PFS) as their primary endpoint had low reporting rate. There were no other statistically significant differences. Reporting post-protocol therapy has not changed over time with reported data in 50% and 52% studies between 2000-2010 and 2011-2023, respectively. CONCLUSIONS Data on post progression therapy in trials supporting FDA approval of drugs for MBC are available in fewer than half of indications. Reported data are often partial and may not include sequential therapies consistent with standard of care. As subsequent lines of therapy may have a crucial role in patients' outcome, post protocol reporting should be included in the regulatory submission and be made available publicly. Differences between studies with and without data on post progression therapy Citation Format: Shlomit Shachar, Yasmin Korzets, Daniel Shepshelovich, Noa Zlotchover, Eitan Amir, Ariadna Tibau, Hadar Goldvaser. Reporting of Post-protocol Therapies in Metastatic Breast Cancer Registration Clinical Trials: A Systematic Review [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-11-02.

Abstract PO2-27-06: ANXA9 facilitates the exocrine secretion of S100A4 and promotes pleural metastasis in breast cancer

Abstract Metastasis to distant organs stands as the primary contributor to mortality in cases of breast cancer. While localized breast cancer boasts a 5-year survival rate of roughly 99%, this figure drastically declines to approximately 26% for patients afflicted with distant metastasis. Regrettably, the current therapeutic landscape lacks efficacious and targeted interventions for the treatment of metastatic breast cancer. Our investigation has revealed a significant upregulation of S100A4 in metastatic breast cancer tissues, with notably high expression observed in the malignant pleural effusion of patients in advanced stages of the disease. Upon acceptance of the effective treatment, the expression of S100A4 in malignant pleural effusion decreased, along with a decrease in several cytokines, including IL-6, IL-8, CCL2, and CCL5. The breast cancer cellular models demonstrated that ANXA9 has the ability to regulate the excretion of S100A4 from cells into the surrounding medium. Similarly, the mice model of pleural metastasis indicated that the downregulation of ANXA9 (sh-ANXA9) resulted in decreased levels of S100A4 and cytokines IL-6, IL-8, CCL2, and CCL5 in the mice's hydrothorax. Additionally, our findings suggest that ANXA9 regulates the excretion of S100A4 through phosphorylation of ANXA9. The cellular membrane harbored phosphorylated ANXA9, which exhibited two phosphorylation sites. Upon mutation of these sites, the level of ANXA9 phosphorylation decreased, leading to a reduction in the exocrine release of ANXA9 from cells into the medium. Our research further revealed the significant involvement of ANXA9 in facilitating the progression of breast cancer, thereby suggesting that therapeutic interventions targeting ANXA9 could prove efficacious in treating metastatic breast cancer. This work was supported by Shanghai Sailing Program to Dengfeng Li (No. 20YF1437800), grant from the National Natural Science Foundation of China to Dengfeng li (No. 82103454) and grant from the National Natural Science Foundation of China to Lin Fang (No. 82073204). Citation Format: Xiqian Zhou, Dengfeng Li, Lin Fang, Junyong Zhao. ANXA9 facilitates the exocrine secretion of S100A4 and promotes pleural metastasis in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-06.