HER2-positive Breast Cancer Patients Research Articles

HER2/neu 655 polymorphism, trastuzumab-induced cardiotoxicity, and survival in HER2-positive breast cancer patients.

HER2 overexpression in breast cancer correlates with poor outcomes. The incorporation of Trastuzumab into the treatment regimen has notably improved patient prognoses. However, cardiotoxicity emerges in approximately 20% of patients treated with the drug. This study aims to investigate the association between the HER2 655 A > G polymorphism, Trastuzumab-induced cardiotoxicity, and patient survival. The study involved 88 patients treated with Trastuzumab. Cardiotoxicity, defined as a reduction in left ventricular ejection fraction (LVEF) from baseline or the emergence of clinical signs of congestive heart failure, was identified during treatment follow-up. Genotyping of HER2 655 A > G employed TaqMan SNP technology. Genotype frequencies of HER2/neu 655 (53 AA, 32 AG, and 3 GG) were consistent with Hardy-Weinberg equilibrium. No significant differences were observed in mean baseline LVEF between patients who developed cardiotoxicity and those who did not. Within these groups, neither AA nor AG genotypes showed an association with changes in mean baseline or reduced LVEF levels. Logistic regression analysis, adjusted for hormonal status and anthracycline treatment, revealed that AG genotype carriers face a significantly higher risk of cardiotoxicity compared to AA carriers (OR = 4.42; p = 0.037). No association was found between the HER2/neu 655 A > G polymorphism and disease-free or overall survival, regardless of whether the data was adjusted for stage or not. HER2 655 A > G polymorphism is significantly linked to an increased risk of Trastuzumab-induced cardiotoxicity but does not correlate with variations in disease-free survival or overall survival rates.

GDF-15 is a potential candidate biomarker for an elevated risk of cardiotoxicity in breast cancer patients receiving neoadjuvant dual anti-HER2 therapy

ObjectiveGrowth differentiation factor 15 (GDF-15) is a stress-responsive cytokine that regulates myocardial injury, cardiac overloading pressure, and inflammation and is related to the risk of cardiovascular diseases and events. The current study aimed to investigate the correlation of GDF-15 levels with clinical features, biochemical indices, and especially the risk of cardiotoxicity in breast cancer patients receiving neoadjuvant dual anti-HER2 therapy.MethodsA total of 103 HER2-positive breast cancer patients who underwent neoadjuvant dual anti-HER2 therapy (trastuzumab and pertuzumab plus chemotherapy) were included. Serum GDF-15 levels before neoadjuvant treatment were detected by enzyme-linked immunosorbent assay. Cardiotoxicity was evaluated during neoadjuvant therapy by referring to a decline of ≥10 percentage points in the left ventricular ejection fraction from baseline to an absolute level less than 50%.ResultsGDF-15 exhibited a skewed distribution, with a median level of 714 (range: 207–1805) pg/mL. GDF-15 was positively correlated with age (p = 0.037), diabetes (p = 0.036), and the N-terminal pro-brain natriuretic peptide level (p = 0.013) and positively correlated with the total cholesterol level (p = 0.086) and troponin T level (p = 0.082), but these correlations were not statistically significant. A total of 6.8% of patients experienced cardiotoxicity during neoadjuvant therapy. By comparison, the GDF-15 level was greater in patients who experienced cardiotoxicity than in those who did not (p = 0.008). A subsequent receiver operating characteristic curve revealed that GDF-15 predicted cardiotoxicity risk, with an area under the curve of 0.803 (95% CI: 0.664–0.939). After multivariate adjustment, GDF-15 independently predicted a greater risk of cardiotoxicity (p = 0.020).ConclusionGDF-15 is a candidate biomarker for increased risk of cardiotoxicity in breast cancer patients receiving neoadjuvant dual anti-HER2 therapy.

Abstract PO4-16-06: From Real-World Data to Improved Outcomes: Examining the Impact of Trastuzumab Disparities on Pathological Complete Response and Long-Term Survival in HER-2 Positive Breast Cancer Patients within the Brazilian Public Health System

Abstract Introduction: Equitable access to healthcare is a fundamental principle of public health, aiming to ensure that all individuals have the opportunity to receive effective treatments. However, disparities in access to healthcare still persist in many countries, including Brazil. These disparities can have significant impacts on the health and well-being of patients, particularly in the case of breast cancer treatment. Neoadjuvant chemotherapy (NAC) has been increasingly used for the treatment of breast cancer, encompassing conditions ranging from locally advanced tumors to early-stage triple-negative and HER-2 positive tumors. Objectives: The aim of this study is to evaluate the impact of disparities in the use of trastuzumab (Herceptin) within the Brazilian public health system on pathological complete response (pCR), overall survival (OS), and disease-free survival (DFS). We aim to investigate whether variations in access to trastuzumab treatment influence the achievement of pCR and impact long-term survival outcomes in breast cancer patients. Methods: This retrospective, multicenter cohort study included female patients over 18 years of age with a diagnosis of non-metastatic breast cancer undergoing NAC. pCR was defined as the absence of residual invasive or in situ tumor in the breast and axilla. As an exploratory real-world data study, no confirmatory hypothesis was established, thus no corrections for multiple comparisons were necessary. Overall survival (OS) and disease-free survival (DFS) were estimated using the Kaplan-Meier method, calculated at five years. The study was approved by the Research Ethics Committee with registration number CAAE 64633422.4.0000.5463. Results: Between 2011 and 2020, a total of 1,891 patients were included in the study, of whom 454 (22.9%) were HER-2 positive. The pCR rate was 25.7%. Trastuzumab was accessed by 291 (64.1%) patients (p < 0.001). Among those who received trastuzumab, pCR was observed in 105 (36.1%) patients, compared to 12 (7.6%) in those who did not have access to trastuzumab (p < 0.001). OS in HER-2 positive patients was 90.1% with pCR and 64.5% without pCR (log-rank p < 0.001), while DFS was 89.2% with pCR and 68.2% without pCR (log-rank p = 0.003). Evaluating OS and DFS in patients who received trastuzumab versus those who did not, OS with trastuzumab and pCR was 94.3% and without pCR was 89.5% (log-rank p < 0.001); OS without trastuzumab and pCR was 83.3% and without pCR was 58.2% (log-rank p < 0.001). DFS in patients who received trastuzumab and achieved pCR was 94.5% and without pCR was 90.5% (log-rank p = 0.05), whereas without trastuzumab and pCR was 79.9% and without pCR was 62.1% (log-rank p = 0.001). Conclusion: These findings underscore the significant impact of disparities in trastuzumab utilization within the Brazilian public health system on pCR rates and long-term survival outcomes in HER-2 positive breast cancer patients. Access to trastuzumab was associated with higher pCR rates and improved overall and disease-free survival rates. Ensuring equitable access to targeted therapies is crucial for improving treatment response and long-term outcomes in breast cancer patients. Table 1 Clinicopathological characteristics of patients Legend: AJCC, American Joint Committee on Cancer; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; HR hormonal receptor. Table 2 - NAC schemas and correlation with pCR. AC-T, doxorubicin + cyclophosphamide – taxane; AC-TH, doxorubicin + cyclophosphamide – taxane+herceptin. Citation Format: Marcelo Antonini, Andre Mattar, Gabriel Pannain, Fernanda Grace Bauk Richter, Andressa Amorim, Marina Diogenes, Odair Ferraro, Luiz Gebrim, Reginaldo Coelho Lopes, Juliana Real. From Real-World Data to Improved Outcomes: Examining the Impact of Trastuzumab Disparities on Pathological Complete Response and Long-Term Survival in HER-2 Positive Breast Cancer Patients within the Brazilian Public Health System [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 PO4-16-06.

Abstract PO3-01-01: Dysregulation of Phenylalanine-tyrosine Metabolic Signaling Pathway and Neoadjuvant Response in HER2-positive Breast Cancer

Abstract Background: Although trastuzumab and tyrosine inhibitors combined with neoadjuvant chemotherapy could significantly improve patients' pathological complete response (pCR) rate, nearly half of the patients could not achieve complete remission. Our objective was to explore the relationship between metabolic signaling pathway changes and therapeutic efficacy in patients receiving neoadjuvant therapy for HER2-positive breast cancer. Methods: Core needle biopsy specimens from HER2-positive breast cancer patients who underwent neoadjuvant therapy and radical mastectomy at Fudan University Shanghai Cancer Center between January 2017 and December 2021 were collected for RNA sequencing. According to pathological evaluation, samples (n=133) were divided into pCR and non-pCR groups. Gene differences between the two groups were further evaluated for KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis. The TCGA (The Cancer Genome Atlas, n=1091) and the HAN ethnic GEO datasets (GSE162228, GSE206, GSE48391, n=305) were used to analyze the metabolic differences between tumors and normal tissues with patients’ prognosis. Consensus clustering analysis was performed to divide patients for low and high phenylalanine-tyrosine metabolism dysregulation to analyze patients’ outcomes. The IC50 value of cell lines was tested using CCK-8 experiments. Western blot was performed to analyze the protein level changes in mTOR and glycolysis pathway. Results: We found that phenylalanine-tyrosine metabolism was significantly enriched in HER2-positive breast cancer patients. Consensus clustering analysis of TCGA and the HAN ethnic GEO datasets showed that patients with low phenylalanine-tyrosine catabolism had a significantly worse survival outcome than patients with high tyrosine metabolism (P= 0.017). In our cohort, phenylalanine-tyrosine pathway metabolic enzyme DDC was upregulated while MAOA was downregulated in non-pCR patients compared to pCR patients, suggesting the increased production of dopamine and reduced catabolism of dopamine (DA) in non-pCR tumors. In vitro experiments showed that dopamine and the knockdown of MAOA decreased cell sensitivity to pyrotinib. In addition, dopamine and clorgyline- an MAOA inhibitor, promoted the proliferation of HER2-positive cell lines under the treatment of pyrotinib. The GSEA analysis of our neoadjuvant cohort and TCGA datasets revealed that MAOA expression was associated with an inverse enrichment of the mTORC1 and glycolysis pathways. Western blot experiment results showed that dopamine or the knockdown of MAOA could activate the mTOR and glycolysis pathway Conclusions: Phenylalanine-tyrosine metabolism was significantly enriched in HER2-positive breast cancer patients. The phenylalanine-tyrosine signaling pathway may be dysregulated in HER2-positive breast cancer and patients with low phenylalanine-tyrosine catabolism have a worse prognosis. Low expression of MAOA promotes tumor resistance to HER2-targeted drugs and could serve as a therapeutic biomarker in breast cancer. Citation Format: Chih Wan Goh, Bingqiu Xiu, Jingyan Xue, Yayun Chi, Jiong Wu. Dysregulation of Phenylalanine-tyrosine Metabolic Signaling Pathway and Neoadjuvant Response in HER2-positive 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 PO3-01-01.

Abstract PO3-08-10: Somatic mutations of a multigene panel in Chinese HER2-positive patients undergoing neoadjuvant therapy and impact on prognosis based on TP53 status:a single-institution retrospective cohort

Abstract Background: Gene mutations and copy number variations (CNVs) are associated with the occurrence and development of tumors. Neoadjuvant therapy (NAT) has shown greater clinical benefit in the treatment of HER2-positive breast cancer (BC). The impact of genetic mutations on NAT efficacy in BC has been frequently reported, but the relationship between genetic mutations and NAT efficacy and the long-term prognosis in HER2-positive BC patients still requires more high-quality studies. Methods: This retrospective cohort study was conducted patients receiving NAT between September 2017 and March 2021 in the Department of Breast Surgery of Fudan University Shanghai Cancer Center (FUSCC). The genomic characteristics of 513 cancer-related genes from the archived tumour blocks were assessed by next-generation sequencing (NGS). The relationship between tumour mutated gene and the postoperative pathological complete response (pCR) as well as prognosis of the disease-free survival (DFS) were further explored.Statistical methods included Chi-square test, fisher's exact test, Kaplan-Meier survival analysis, all of which were completed by SPSS 20.0. Results: 208(47.8%) patients achieved pCR after HER2-targeted NAT and 40(9.2%) patients encountered DFS events. The frequency of somatic alterations in TP53(60%), PIK3CA (15%) and ERBB2(11%) was highest in women with HER2-positive breast cancer. KMT2C (P= 0.036) and TP53(P=0.037) mutations were significantly increased in patients with DFS events. In the HER2+/HR- cohort, patients who achieved pCR had significantly benefit in prognosis (HR=3.605, P=0.002), and CCND1 amplifications(p=0.014), ATM(p=0.016) and GATA3(p=0.016) mutations were more frequent. ERBB2 mutations were significantly associated with younger ages of diagnosis(p=0.018). TP53 mutations were associated with worse DFS (HR=3.242, P=0.0110) as well as more DFS events(p=0.048). Furthermore, TP53 mutations had significant prognostic importance in HER2-positive BC patients with HR-negative (HR=3.712, P=0.0266), pCR (HR=6.253, P=0.0268) and who received trastuzumab-only targeted therapy (HR=4.145, P=0.0105). Conclusions: Regard to diverse hormone receptor status or neoadjuvant efficacy, the genetic mutation maps of Chinese HER2+ patients receiving NAT are disparate. Our study found that TP53 mutations have significant prognostic value in patients with NAT for HER2-positive BC and patients benefit differently depending on HR status, neoadjuvant regimens and response. Citation Format: Min Xiong, Liren Wangxu, Jingyan Xue, Benlong Yang, Jiong Wu. Somatic mutations of a multigene panel in Chinese HER2-positive patients undergoing neoadjuvant therapy and impact on prognosis based on TP53 status:a single-institution retrospective 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 PO3-08-10.

Abstract PO5-18-10: Omission of SLNB in triple-negative and HER2-positive breast cancer patients with radiologic and pathologic complete response in the breast after NAST: a single-arm, prospective surgical trial (EUBREAST-01 trial, GBG 104)

Abstract Background: Currently, axillary surgery for breast cancer is considered a staging procedure that does not seem to influence breast cancer mortality since the risk of developing metastasis depends mainly on the biological behavior of the primary (seed-and-soil model). Based on this, postsurgical therapy should be considered based on biological tumor characteristics. Retrospective data of cancer registry trials showed a strong correlation between breast pathologic complete response (pCR) and nodal pCR depending on intrinsic subtypes. Improvements in systemic treatments for breast cancer have increased the rates of pCR in patients receiving neoadjuvant systemic therapy (NAST), offering the opportunity to decrease, and perhaps eliminate, surgery in patients who have a pCR. Trial design: The EUBREAST network designed a clinical trial (NCT04101851) in which only patients with the highest likelihood of having a pCR after NAST (triple-negative or HER2-positive breast cancer) will be included, and type of surgery will be defined according to the response to NAST rather than on the classical T and N status at presentation. In the ongoing trial, axillary surgery will be eliminated (no axillary sentinel lymph node biopsy [SLNB]) for initially clinical node-negative (cN0) patients with radiologic complete remission (rCR) and a breast pCR (ypT0/ypTis) as determined in the lumpectomy specimen. The trial design is a multicenter single-arm study with a limited number of patients (N=440 as the screening population with an expected 80% pCR-rate) which might give practice-changing results in a short period, sparing the time and the costs of a randomized comparison. Patients will be recruited in European countries (Austria, Germany, Italy, and Spain) over 48 months. Inclusion criteria: -Written informed consent -Histologically confirmed unilateral primary invasive carcinoma of the breast (core biopsy). Multifocal or multicentric tumors are allowed if breast-conserving surgery (BCS) is planned. -Age at diagnosis at least 18 years -imaging techniques with estimated tumor stage between cT1-T3 before NAST -triple-negative (TNBC) or HER2-positive invasive breast cancer -TNBC is defined by: ER-negative (< 10% positive cells in IHC) and PgR-negative (< 10% positive cells in IHC), HER2-negative -clinically and sonographically tumor-free axilla before core biopsy (cN0/iN0) -in cases with cN0 and iN+, a negative core biopsy or fine-needle aspiration biopsy of the sonographically suspected lymph node is required -no evidence for distant metastasis (M0) -standard NAST with rCR -planned BCS with postoperative external whole-breast irradiation (conventional fractionation or hypofractionation) Primary objective: 3-year rate of axillary recurrence-free survival (ARFS) after BCS Statistics: The calculated total case number for per-protocol analysis is N=350, and the expected total number of screened patients is N=440. The assumption for acceptable 3-year ARFS ≥98.5% in the experimental arm is based on previous study findings. Timelines: -First patient in: January 2021 -Last patient in: December 2024 -Primary outcome analysis: Q1/2027 Current accrual: In June 2023, 255 patients were recruited; the majority of them in Germany. Contact: Prof. Dr. Toralf Reimer (eubreast-01@kliniksued-rostock.de), study chair Dr. Oreste D. Gentilini (gentilini.oreste@hsr.it), study co-chair Funding by Else Kroener-Fresenius Foundation, German Society of Senology, University of Rostock (Germany), and San Raffaele Hospital (Milan, Italy). Citation Format: Toralf Reimer, Bernd Gerber, Thorsten Kuehn, Nikola Bangemann, Anke Kleine-Tebbe, Andrea Stefek, Ulrike Doerste, Carolin Hammerle, Oliver Hoffmann, Alexander Hein, Isabel Rubio, Florentia Peintinger, Keyur Mehta, Sibylle Loibl, Edoardo Botteri, Oreste Gentilini. Omission of SLNB in triple-negative and HER2-positive breast cancer patients with radiologic and pathologic complete response in the breast after NAST: a single-arm, prospective surgical trial (EUBREAST-01 trial, GBG 104) [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 PO5-18-10.

Abstract PO5-24-10: Clinical significance and immune landscape analyses of the immune related genes based prognostic signature for HER2 positive breast cancer

Abstract Objective: To date, significant breakthrough has yet to be achieved in immunotherapy for HER2-positive breast cancer (HPBC). In this study, we aimed to construct a risk model for predicting prognosis and therapy response and evaluating the tumor immune landscape in HPBC patients. Methods: Differentially expressed immune-related genes (IRGs) were used as input to weighted correlation network analysis (WGCNA) to identify modules of highly correlated gene. An optimal prognostic TPBC-IRGs signature were constructed by least absolute shrinkage and selection operator (LASSO) cox regression. Survival analysis and ROC curves were analyzed to identify the predictive value in a training cohort and external validation cohorts. With three GEO datasets and samples from our center, the anti-HER2 therapeutic efficacy in HPBC patients was predicted through this prognostic model. Additionally, the immunotherapy outcome was forecasted using IMvigor210 dataset. We also investigated the connection between high and low-risk populations and immune checkpoints and analyzed immune infiltration levels of these populations with several algorithms. Ultimately, we develop a combined model and nomogram by integrating the risk score with clinical factors. Results: 11 key genes associated with overall survival (OS) in the blue module were selected for further analysis. A 3-gene signature (CX3CL1, RARB, TANK) based prognostic risk model was developed. The Kaplan-Meier survival curve revealed that patients with high-risk score had shorter OS compared with the low-risk group. The AUC of the training cohort at 1-, 3- and 5-year were 0.718, 0.784 and 0.767. The performance of the risk model was validated with GSE25066 and GSE55348. It’s showed that the risk scores of HPBC who were resistant to trastuzumab were significantly higher than those of patients who were sensitive to trastuzumab. The results indicated that the levels of immune checkpoints expression (such as PD-1, CTLA4 and TIGIT) and immune infiltration were higher in low-risk group than in high-risk group. The combined model showed better prognostic prediction accuracy compared to the clinical model or gene signature alone (1-year AUC=0.910;3-year AUC=0.832;5-year AUC=0.882). Conclusion: The immune gene-based risk profile and combined prognostic model in this study may hold promise for clinical use in predicting the prognosis and treatment efficacy of HPBC patients. figure3. Construction of HPBC-IRGs signature based prognostic model. Citation Format: Xiaofen Li, Wenfen Fu, Yushuai Yu, Jie Zhang, Chuangui Song. Clinical significance and immune landscape analyses of the immune related genes based prognostic signature for HER2 positive 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 PO5-24-10.

Role of Early Left Atrial Functional Decline in Predicting Cardiotoxicity in HER2 Positive Breast Cancer Patients Treated With Trastuzumab

Trastuzumab is widely used in HER2 breast cancer. However, it may cause left ventricular (LV) dysfunction. A decrease in LV global longitudinal strain (GLS) has been previously demonstrated to be a good predictor of subsequent cancer therapy related dysfunction (CTRCD). Left atrial morphological remodeling during Trastuzumab therapy has also been shown. The aim of this study is exploring the relationship between early changes in left atrial function and the development of Trastuzumab-induced cardiotoxicity. Consecutive patients with diagnosis of HER2+non-metastatic breast cancer treated with Trastuzumab were prospectively enrolled. A clinical, conventional, and advanced echocardiographic assessment was performed at baseline and every three months, until a one-year follow-up was reached. One-hundred-sixteen patients completed the 12 months follow-up, 10 (9%) cases of CTRCD were observed, all after the sixth month. GLS and LVEF significantly decreased in the CTRCD group at 6 months of follow-up, with an earlier (3 months) significant worsening in left atrial morpho-functional parameters. Systolic blood pressure, early peak atrial longitudinal strain (PALS), peak atrial contraction (PACS) and left atrial volume (LAVI) changes resulted independent predictors of CTRCD at multivariable logistic regression analysis. Moreover, early changes in PALS and PACS resulted good predictors of CTRCD development (AUC 0.85; p = 0.008, p < 0.001 and 0.77; p = 0.008, respectively). This prospective study emphasizes that the decline in PALS and PACS among trastuzumab-treated patients could possibly increase the accuracy in identifying future CTRCD in non-metastatic HER2 breast cancer cases, adding predictive value to conventional echocardiographic assessment.

Abstract PO2-16-12: Real world evidence of neoadjuvant chemotherapy for breast cancer treatment in a Brazilian multicenter cohort: correlation of pathological complete response and overall survival

Abstract Introduction: Breast cancer is the most common malignancy among women in Brazil and worldwide. Neoadjuvant chemotherapy (NAC) has been increasingly used for the treatment of breast cancer conditions ranging from locally advanced tumors to early-stage triple-negative and HER-2 positive tumors. Nowadays only 5% of breast cancer patients are enrolled in clinical trials. Real-world data is important to evaluate how clinical trial treatments behave in the real world with all the heterogeneous patient characteristics of those treated differently from the homogeneity of clinical trials. Objectives: To evaluate the rates of pathological complete response (pCR) in patients undergoing neoadjuvant chemotherapy (NAC) for the treatment of breast cancer (BC) To examine the differences in pathological complete response (pCR) rates between HER-2 positive breast cancer patients with and without trastuzumab treatment, and between triple-negative breast cancer (TNBC) patients with and without platinum-based treatment, Additionally, we aim to assess the impact of pCR on overall survival (OS) and disease-free survival (DFS) using real-world data (RWD). Methods: This was a retrospective, multicentric cohort study, that included female patients over 18 years of age, with a diagnosis of non-metastatic breast cancer undergoing NAC. As an exploratory real-world data study, no confirmatory hypothesis was established, so no corrections for multiple comparisons were necessary. Overall survival (OS) and disease-free survival (DFS) were estimated by the Kaplan-Meier method calculated at five years. Additionally, we conducted a multivariate analysis to identify significant associations with pathologic complete response (pCR) and overall survival (OS). We employed a forest plot to visually represent these associations Results: From 2011 to 2020, 1,891 patients were included in the study, and 421 (22,3%) achieved pCR (ypT0 ypN0) and considering the presence of residual in situ carcinoma (DCIS) the pCR was seen in 467 patients (23,5) without significant difference (p=0,567) . The pCR rate varied between the subtypes: luminal A 17,0%, luminal B 21,3%, luminal HER2 23,0%, TNBC 22,5% and HER2 28,5% (p = 0,057). The type of neoadjuvant chemotherapy (NAC) regimen was correlated with pathological complete response (pCR). Among HER2-positive patients, those who received Trastuzumab had a significantly higher rate of pCR compared to those who did not receive it (p &amp;lt; 0.0001). Similarly, in patients with TNBC, those who underwent treatment with platinum-based regimens also showed higher rates of pCR (p &amp;lt; 0.0001). There were 694 deaths, and the 5-year OS rate was 62.9%. OS was also grouped according to pCR status, and pCR OS rate was 88,3% and non-pCR 58.1% significant difference observed (p &amp;lt; 0.0001). Five-year DFS of pCR was 92.2% and non-pCR 64.3% (p &amp;lt; 0.0001). Conclusion: this real-world data study evaluated the rates of pathological complete response (pCR) in breast cancer patients undergoing neoadjuvant chemotherapy (NAC). The results revealed varying pCR rates among different breast cancer subtypes, with HER2-positive and triple-negative subtypes showing higher rates. The use of Trastuzumab in HER2-positive patients and platinum-based regimens in triple-negative patients correlated with significantly higher pCR rates. Furthermore, achieving pCR was associated with improved overall survival (OS) and disease-free survival (DFS). These findings emphasize the importance of considering individual tumor characteristics and tailoring treatment strategies for breast cancer patients to optimize outcomes. Clinicopathological characteristics of patients AJCC, American Joint Committee on Cancer; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; TNBC triple negative breast cancer. NAC schemas and correlation with pCR. AC-T, doxorubicin + cyclophosphamide – taxane; AC-TPlatinum, doxorubicin + cyclophosphamide – taxane+carboplatin; AC-TH, doxorubicin + cyclophosphamide – taxane+herceptin. Citation Format: Marcelo Antonini, Andre Mattar, Fernanda Grace Bauk Richter, Gabriel Pannain, Andressa Amorim, Marina Diogenes, Odair Ferraro, Luiz Gebrim, Reginaldo Coelho Lopes, Juliana Real. Real world evidence of neoadjuvant chemotherapy for breast cancer treatment in a Brazilian multicenter cohort: correlation of pathological complete response and overall survival [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 PO2-16-12.

Abstract PO1-16-05: Matched multi-analyte and multi-omic liquid biopsy of cell-free DNA, circulating tumor cells and extracellular vesicles in HER2-positive metastatic breast cancer patients

Abstract Background: Liquid biopsy, specifically cell-free DNA (cfDNA) mutation analysis, has recently entered clinical practice for treatment decision-making in hormone receptor (HR)-positive (+)/HER2-negative (-) metastatic breast cancer (mBC) patients. However, we showed that the analysis of multiple liquid biopsy analytes in the course of treatment in this BC subgroup has additive value. Since no multi-analyte studies are currently available for the subgroup of HER2+ mBC patients, we here studied multiple analytes [cfDNA, circulating tumor cells (CTCs) and extracellular vesicles (EVs)] and utilized our multi-omics perspective (CpG island methylation, mutations and mRNA expression) to get insight into their utility in therapy management of HER2+ mBC. Methods: 2x 9 ml blood was drawn from 21 HER2+ (HR+ n=16 and HR- n=5) mBC patients at the time of disease progression and at two consecutive staging time points. CTCs and their mRNA were isolated from 2x5 ml blood by positive immunomagnetic selection targeting EpCAM, EGFR and HER2 (AdnaTest EMT2/StemCell Select/Detect). Plasma of CTC-depleted blood was used for cfDNA isolation, while mRNA from EVs was isolated from 4 ml pre-filtered plasma by affinity-based binding to a spin column (exoRNeasy) using the remaining blood. The mRNA purified from CTCs and EVs by Oligo-dT beads was reverse transcribed, pre-amplified and analyzed by a multi-marker (18 genes) qPCR panel. qPCR data was normalized to CD45 (for CTC analysis) and data of 20 healthy female donor controls to identify BC specific overexpression signals with a specificity of &amp;gt;90% for all targets. Variants in the cfDNA were analyzed with a customized QIAseq Targeted DNA Panel with unique molecular indices (UMIs) and high coverage (mean 22.000x), while CpG island methylation in the cfDNA was analyzed with a customized QIAseq Targeted Methyl Panel with UMIs covering 9786 CpG sites (mean 900x). Consumables: QIAGEN, Germany. Results: In general, substantial differences occurred between the CTC and EV mRNA profiles. Transcripts involved in the PI3K pathway (mTOR, AKT2, PIK3CA) as well as ERBB2 signals were significantly more prevalent in CTCs compared to EVs and mTOR, ERCC1, SRC, AKT2 und PIK3CA CTC overexpression signals were found in &amp;gt;50% of these patients. In contrast, PARP1, AURKA, SRC und ERCC1 signals were significantly more prominent in the EVs and detected in &amp;gt;50% of the patients. ERCC1 signals were present in EVs with highest prevalence whereas ERBB2 signals were only present in CTCs. ERBB3+ CTCs were only detected in patients showing disease progression. Currently, cfDNA mutations as well as cfDNA CpG island methylation are under evaluation and the complete multi-analyte and multi-omic data set as well as their relation to clinical outcome will have been finalized to be presented at the meeting. Conclusion: We successfully established a workflow for parallel isolation of multiple liquid biopsy analytes from a minimized blood volume in HER2+ mBC. Preliminary mRNA profile results for CTCs and EVs show the complementary nature of these two liquid biopsy analytes. Besides the multi-analyte nature of this workflow, the pending results for genomic and epigenomic information will show which one of the analytes, alone or in combination, will help to optimize therapy management in HER2+ mBC patients. Citation Format: Sabine Kasimir-Bauer, Markus Storbeck, Ioanna Andreou, Siegfried hauch, Oliver Hoffmann, Rainer Kimmig, Corinna Keup. Matched multi-analyte and multi-omic liquid biopsy of cell-free DNA, circulating tumor cells and extracellular vesicles in HER2-positive metastatic breast cancer patients [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 PO1-16-05.

Abstract PO4-04-06: Exploring the use of tyrosine kinase inhibitors (TKIs) in the management of HER2-positive metastatic breast cancer post trastuzumab emtansine (T-DM1) therapy failure: Insights from a real-world study

Abstract Background Trastuzumab emtansine (T-DM1) is the established standard second-line treatment for HER2-positive metastatic breast cancer (MBC) patients who have previously received trastuzumab. However, there is ongoing debate regarding the subsequent therapeutic options following T-DM1 failure. This study aimed to evaluate the efficacy and safety of tyrosine kinase inhibitors (TKIs)-based therapy in HER2-positive MBC patients with resistance to T-DM1. Methods During the period from September 2018 to October 2021, a multicenter real-world study was conducted, enrolling a total of 53 patients diagnosed with HER2-positive metastatic breast cancer (MBC). These patients underwent TKIs-based therapy following the failure of T-DM1 treatment. The primary focus of the study was on evaluating progression-free survival (PFS) as the main endpoint. Secondary endpoints encompassed objective response rate (ORR), overall survival (OS), clinical benefit rate (CBR), and safety assessments. Results A total of 53 patients received TKIs-based therapy as a second-line or later treatment. The median progression-free survival (PFS) for TKIs-based therapy was 11.9 months (95% CI 7.9-15.9). The objective response rate (ORR) and clinical benefit rate (CBR) were found to be 19.6% and 72.5%, respectively. Among patients with brain metastasis (n=12), a median PFS of 10.5 months (95% CI 7.5-13.5) and an intracranial ORR of 33.3% were observed. Patients treated with pyrotinib (n=21) showed improved PFS compared to those treated with lapatinib (n=30), as well as patients who had derived favorable benefit from T-DM1 (PFS ≥ 6 months). Hormone receptor status (HR) and response to T-DM1 were identified as independent factors affecting the effectiveness of TKIs-based therapy. The most frequently reported adverse events included thrombocytopenia (23.6%), diarrhea (15.7%), leucopenia (15.7%), and hand-foot syndrome (15.7%). Conclusion TKIs-based therapy demonstrated favorable effectiveness and safety in HER2-positive metastatic breast cancer (MBC) patients who had previously received T-DM1 but experienced treatment failure. This includes patients with brain metastases. Notably, individuals who derived favorable benefits from prior T-DM1 treatment displayed significantly prolonged progression-free survival (PFS) when undergoing subsequent TKIs-based therapy. Citation Format: Yongmei Yin, Chunxiao Sun, Yijia Hua, Nan Jin, Wei Li, Xiang Huang. Exploring the use of tyrosine kinase inhibitors (TKIs) in the management of HER2-positive metastatic breast cancer post trastuzumab emtansine (T-DM1) therapy failure: Insights from a real-world study [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 PO4-04-06.

Abstract PO1-04-02: ACE-Breast-03: A phase 2 study of ARX788, a novel next-generation anti-HER antibody-drug conjugate in HER2-positive metastatic breast cancer patients previously treated with trastuzumab deruxtecan

Abstract Background: HER2 overexpression and/or amplification confers aggressive tumor behavior and decreased survival in patients with breast cancer. Targeting of HER2 is a validated therapeutic strategy, and trastuzumab deruxtecan (T-DXd) has emerged as a preferred treatment in the second-line setting. However, effective treatment following progression on T-DXd remains a major unmet medical need. ARX788 is a next-generation antibody-drug conjugate (ADC) using a technology platform whereby a HER2-specific monoclonal antibody is conjugated to amberstatin 269 (AS269), a potent cytotoxic tubulin inhibitor. Site-specificity, high homogeneity, and stable covalent conjugation of ARX788 leads to the slow release and prolonged peak of serum pAF-AS269, which may contribute to the lower systemic toxicity and increased targeted delivery of payload to tumor cells, at a lower effective dose compared with other HER2 ADCs. Methods: ACE-Breast-03 (NCT04829604) is a global, phase 2 study designed to assess anticancer activity and safety in approximately 40 patients with unresectable or metastatic HER2 positive breast cancer who have been previously treated with T-DXd. Eligibility criteria include measurable disease by RECIST v1.1, radiographically stable brain metastases, no more than three prior lines of treatment in the metastatic setting, and HER2 positivity as determined by central review. If recently progressed on T-DXd or trastuzumab emtansine (T-DM1), a new biopsy for HER2 status is required. Patients will be administered 1.5 mg/kg of ARX788 every three weeks. Efficacy will be assessed using RECIST v1.1 at nine-week intervals after starting ARX788 until progression or start of new cancer treatment. Objective response rate is the primary endpoint, with disease control rate, progression-free survival, overall survival, best overall response, duration of response, and time to response as additional endpoints. The safety and tolerability profile will also be evaluated. PK analysis will determine serum concentrations of ARX788, total antibody, and pAF-AS269. Potential predictive and/or prognostic biomarkers will be analyzed for exploratory purposes. Descriptive statistics will be used to evaluate anticancer activity, safety, and tolerability. The study is currently recruiting patients. Citation Format: Kashif Ali, Laila Agrawal, Anu Thummala, Kevin Kalinsky, Sami Ali, Sibel Blau, Margaret Block, Michael Danso, Denise Yardley, Jay Andersen, Adrienne Gropper-Waks, Priya Jayachandran, Igor Makhlin, Petros Nikolinakos, Joyce O'Shaughnessy, Sandra Aung, Colin Hessel, Hope Rugo, William Gradishar, Debu Tripathy. ACE-Breast-03: A phase 2 study of ARX788, a novel next-generation anti-HER antibody-drug conjugate in HER2-positive metastatic breast cancer patients previously treated with trastuzumab deruxtecan [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 PO1-04-02.

Abstract PO5-15-07: Integrative proteomics, phosphoproteomics, and RNA profiling revealed novel timeline-dependent vulnerabilities in HER2-positive breast cancer

Abstract Background: Most personalized breast cancer therapies leverage biomarkers identified in the pre-treatment setting. They do not always reflect the dynamic nature of early indicators of treatment response/resistance. Herein, we have a unique cohort of newly diagnosed HER2-positive breast tumors treated with a single low dose of trastuzumab (50mg), and the corresponding residual tumors that did not achieve pathologic complete response (pCR) to HER2-targeted neoadjuvant therapy. We hypothesize that integrative molecular profiling with proteomics and transcriptomics of these breast tumors could reveal novel time-course dependent contributors of therapy response and resistance. Method: This correlative biomarker study was a secondary objective of a parent study that evaluated 64uc-DOTA-trastuzumab PET imaging to predict response to trastuzumab and pertuzumab-based neoadjuvant therapy in HER2-positive breast cancer patients. Eighteen newly diagnosed breast cancer patients were enrolled, and pCR was achieved in 13 patients (72%). This correlative biomarker study was performed on breast tumors collected within 72 hours following administering a low dose trastuzumab (50mg) to the subjects prior to imaging and neoadjuvant therapy. Deep expression proteomics and phosphoproteomics data acquisition were performed on a Thermo Orbitrap Eclipse mass spectrometer. RNA profiling was performed using Nanostring breast cancer profiler. Results: Our multi-omic approach identified increased abundance or activity in the pCR group on the following (p &amp;lt; 0.05): Her2 protein and ERBB2 transcript levels, increased phosphorylation of ERBB2 (T1052), increase in Golgi trafficking activities, posttranslational modification with protein glycosylation, and lipid biosynthesis. Interestingly, compared to the non-pCR group, the pCR group showed lower activity level in ERBB2’s downstream pathways, such as MAPK, SRC, and PI3K. In the non-pCR group, the residual tumor showed decrease in the following (p &amp;lt; 0.05): Golgi trafficking, glycosylation, antigen processing, and Her2 protein and phosphorylation (T1166). The pCR group had a negative enrichment for SGK1, a kinase which mediates PI3K pathway independently of AKT. SGK1 abundance was highest in residual tumors following neoadjuvant therapy. Conclusion: Using integrative proteomic and RNA profiling, we identified several in-vivo biological pertubations following administration of low dose trastuzumab. Increased Her2 abundance and ERBB2 transcript levels are associated with pCR, in keeping with previous reports of known pCR predictors. Decreased abundance of ERBB’s downstream signaling proteins in the pCR group suggests that early treatment response to trastuzumab may be a predictor of pCR. Our integrative approach identified other dynamic biomarkers. For example, compared to non-pCR group, Golgi trafficking is more active in pCR group tumors, and lowest in residual tumors following neoadjuvant therapy. This suggests that novel Golgi-targeting agents may be best utilized in neoadjuvant setting. Further, we identified SGK1 may be an important kinase for mediating therapy resistance early in treatment course, since its level is higher in non-pCR group following early exposure to trastuzumab compared to pCR group, with highest level detected in the residual tumors. These findings warrant orthogonal validation using in-vitro functional assays. Citation Format: Christina Wei, Lixin Yang, Krystine Mansfield, Jessica Liu, Ritin Sharma, Russell Rockne, Raju Pillai, Patrick Pirrotte, Joanne Mortimer. Integrative proteomics, phosphoproteomics, and RNA profiling revealed novel timeline-dependent vulnerabilities in HER2-positive 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 PO5-15-07.

Abstract PO4-01-04: Clinical significance of Circulating tumor DNA (ctDNA) analysis in predicting pathologic complete remission in HER2-positive Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy

Abstract Background: Neoadjuvant chemotherapy (NACT) combined with dual anti-HER2 agents followed by surgical resection is the standard treatment for stage II-III HER2-positive breast cancer. Despite the availability of effective therapies as an adjuvant treatment such as ado-trastuzumab emtansine (T-DM1) and neratinib, pathologic complete remission (pCR) strongly predicts survival. This study aimed to investigate the role of ctDNA analysis in predicting pCR and clinical outcome using comprehensive ctDNA analysis. Methods: A total of 34 HER2-positive breast cancer patients who underwent NACT combined with dual anti-HER2 agents and surgical resection were enrolled, including 22 clinical stage II and 12 III patients. Plasma samples were collected at four-time points: before neoadjuvant chemotherapy, after 3 cycles, at the completion of neoadjuvant chemotherapy, and after surgery. low-pass whole-genome sequencing (lpWGS) and whole exome sequencing (WES) in evaluating blood copy-number burden (bCNB), genomic alterations, mutational signatures, blood tumor mutational burden (bTMB). Mutations selected from the baseline sample were monitored for Molecular residual disease (MRD) monitoring. lpWGS yielded negative results, targeted NGS sequencing was conducted. Results: Among the enrolled patients (N=34), 21 patients (61.8%) had nodal metastasis and 22 patients (64.7%) were hormone receptor-positive. A total 26 patients (76.5%) achieved pCR. Positive ctDNA was detected in 20 patients (58.8%) at baseline. Higher nodal stage was significantly associated with ctDNA positivity at baseline. After surgery, MRD positivity was observed in 3 patients (8.8%). Among the 26 patents who acheived pCR, only 1 patient (3.8%) showed MRD positivity, while 2 non-pCR patients (25%) demonstrated MRD positivity. Conclusion: The presence of MRD was significantly associated with non-pCR status. The presence of ctDNA at baseline was associated with a higher nodal stage, suggesting its potential as a prognostic marker. Further studies with larger cohorts are warranted to validate these findings and explore the utility of ctDNA analysis for personalized treatment decisions in HER2-positive breast cancer. Citation Format: Byeongju Kang, Soo Jung Lee, Jeeyeon Lee, In Hee Lee, Jee-Young Park, Ho Yong Park, Tiantian Zheng, Lu Tan, Liam Il-Young Chung, Shidong Jia, Pan Du, Young Kwang Chae, Yee Soo Chae. Clinical significance of Circulating tumor DNA (ctDNA) analysis in predicting pathologic complete remission in HER2-positive Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy [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 PO4-01-04.

Abstract PO1-17-03: Real-world evidence of Trastuzumab biosimilars in HER2-positive breast cancer: Evaluating utilization, efficacy, and safety in Taiwan

Abstract Purpose Biosimilars have emerged as a promising alternative to reference biologic products for the treatment of cancers and immunological diseases. With regard to breast cancer, trastuzumab, a reference monoclonal antibody biologic, has been the standard of care for early and advanced HER2-positive breast cancer since 1998. Trastuzumab biosimilars, which provide comparable efficacy at a lower cost, have the potential to reduce financial burden on patients and healthcare systems and improve patient access to HER2-targeted therapy. This study aimed to evaluate the utilization, efficacy, and safety of trastuzumab biosimilars in HER2-positive breast cancer patients at Kaohsiung Veterans General Hospital. Methods A total of 113 HER2-positive breast cancer patients were enrolled between February 2020 and December 2022 and treated with trastuzumab biosimilars (OGIVRI®, trastuzumab-dkst). Of these, 44 were in the neoadjuvant group, 27 in the adjuvant group, and 42 in the metastatic group. Clinical outcomes were evaluated, including pathological complete response (pCR) rate in the neoadjuvant group, objective response rate (ORR) and clinical benefit rate (CBR) in the metastatic group, and safety profile in all groups. Results In the neoadjuvant group, 18 out of 44 evaluable patients achieved pathological complete response after surgery, resulting in a pCR rate of 40.90%. In the metastatic group , the ORR was 57.14% and the CBR was 90.47%. Furthermore, in the metastatic group, treatment with dual blockade using biosimilars resulted in an better ORR of 62.96%. No adverse events of cardiac toxicity were reported in any group. In the adjuvant group, longer follow-up is needed to assess efficacy. Conclusions Our real-world experience suggests that trastuzumab biosimilars are a safe and cost-effective alternative to reference trastuzumab in the treatment of HER2-positive breast cancer. Biosimilar trastuzumab demonstrated efficacy in the neoadjuvant setting, while dual blockade with biosimilars resulted in better disease control in the metastatic setting. Further follow-up is necessary to evaluate the efficacy of trastuzumab biosimilars in the adjuvant setting. Citation Format: Yi-Hung Lo, Yen-Dun Tzeng. Real-world evidence of Trastuzumab biosimilars in HER2-positive breast cancer: Evaluating utilization, efficacy, and safety in Taiwan [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 PO1-17-03.

Abstract PO2-04-05: FINAL OUTCOME ANALYSIS FROM THE PHASE II TUXEDO-1 TRIAL OF TRASTUZUMAB-DERUXTECAN IN HER2-POSITIVE BREAST CANCER PATIENTS WITH ACTIVE BRAIN METASTASES

Abstract Background Brain metastases (BM) are a severe complication of HER2-positive metastatic breast cancer. In the absence of any immediate indication for local therapy, the tyrosine-kinase inhibitor tucatinib combined with trastuzumab and capecitabine (TTC) is regarded as the preferred systemic treatment option for active BM, while data on the activity of antibody-drug conjugates (ADC) is limited. In the primary outcome analysis of TUXEDO-1, an intracranial response rate (RR) of 73.3% was reported with the ADC trastuzumab-deruxtecan (T-DXd). Here, we report final progression-free survival (PFS) and overall survival (OS) results of this study. Patients and Methods: TUXEDO-1 is a prospective, single-centre, single-arm phase 2 trial. Adult patients with HER2-positive BC and active BM (newly diagnosed untreated or progressing after prior local therapy), prior treatment with trastuzumab and pertuzumab, ECOG performance status 0 or 1 without indication for immediate local therapy were accrued and received T-DXd until progression, inacceptable toxicity, or withdrawal for any other reason. The primary endpoint was intracranial RR centrally assessed by Response Assessment in Neuro-Oncology (RANO)-BM criteria in the intention-to-treat population; secondary endpoints included PFS, OS, safety, quality-of-life (QoL), and neurocognitive function. PFS and OS were estimated with the Kaplan-Meier method and analysed in the per-protocol population (PPP). Results A total number of 15 patients were accrued; one patient was found to have dural metastases only upon restaging, resulting in a PPP of 14 patients. Patients had received a median number of two prior treatment lines (range, 1-5), 60% had progressive brain metastases and 60% had received prior T-DM1. At 26.5 months median follow-up, median PFS was 21 months (95% CI 13.3-n.r.) and median OS was not reached (95% CI 22.2-n.r.). A total of 238 cycles of T-DXd were administered (median 11.5 cycles; range 4-42). With longer follow-up, no new safety signals were observed. The most common grade 3 adverse event (AE) was fatigue (n=3; 20%). A total of 8 serious AEs were reported in 8 patients. Grade 2 interstitial lung disease and a grade 3 symptomatic drop of left-ventricular ejection fraction were observed in one patient each. QoL and neurocognitive functioning were maintained over the entire treatment duration and a significant deterioration of global QoL was observed upon progression (p=0.036). Most patients received TTC (n=5) or local therapy (n=4) as next subsequent treatment line. Ancillary biomarker studies are ongoing, and results will be presented at the meeting. Discussion In TUXEDO-1, T-DXd yielded prolonged intra- and extracranial disease control in patients with active HER2-positive breast cancer BM. The safety profile was consistent with previous reports. T-DXd did not impair QoL and neurocognitive functioning was maintained. Results therefore support the concept of ADCs as systemic therapy for active BM. Citation Format: Rupert Bartsch, Anna Sophie Berghoff, Julia Furtner, Maximilian Marhold, Elisabeth Sophie Bergen, Sophie Roider-Schur, Angelika Maria Starzer, Maximilian Mair, Heidrun Forstner, Beate Rottenmanner, Marie-Bernadette Aretin, Karin Dieckmann, Zsuzsanna Bago-Horvath, Helmuth Haslacher, Georg Widhalm, Aysegül Ilhan-Mutlu, Christoph Minichsdorfer, Thorsten Fuereder, Thomas Szekeres, Leopold Oehler, Birgit Gruenberger, Georg Pfeiler, Christian F. Singer, Ansgar Weltermann, Luzia Berchtold, Matthias Preusser. FINAL OUTCOME ANALYSIS FROM THE PHASE II TUXEDO-1 TRIAL OF TRASTUZUMAB-DERUXTECAN IN HER2-POSITIVE BREAST CANCER PATIENTS WITH ACTIVE BRAIN METASTASES [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 PO2-04-05.

Abstract PO1-04-07: Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy and in combination with tucatinib in preclinical breast cancer models

Abstract Disitamab vedotin (DV, RC48-ADC) is an antibody-drug conjugate (ADC) that targets cancers expressing HER2. DV consists of an anti-HER2 monoclonal antibody, disitamab, conjugated with the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a cleavable vedotin linker. DV has multimodal antitumor mechanisms of action that include direct cytotoxicity of HER2-expressing cancer cells and bystander effect-based cytotoxicity of neighboring cells, both of which are mediated by the intracellular release of MMAE. Released MMAE can also induce immunogenic cell death, which promotes immune cell recruitment to the tumor. In addition, DV stimulates Fc-gamma receptor mediated antibody-dependent cellular cytotoxicity, which can lead to target cell death. DV also inhibits HER2-activated downstream signaling pathways, further blocking cell growth, survival, and proliferation. Previously, we showed the cytotoxic activity of DV against a panel of breast cancer cell lines with varying levels of HER2 expression, including the HER2-low range. Here, we sought to further characterize the preclinical antitumor activity of DV in patient-derived 3D models and patient-derived xenographs (PDX). In cultured breast cancer cells, DV was more potent and internalized to a greater magnitude than the HER2-directed ADCs trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd). In patient-derived 3D models, DV had superior activity compared to T-DXd. We further explored whether dual HER2 targeting with DV in combination with the HER2-selective oral TKI tucatinib improved the antitumor outcomes. In PDX models with varying HER2 IHC levels and models refractory to T-DXd, DV as a monotherapy and in combination with tucatinib showed significant tumor growth inhibition. This result is consistent with previous in vitro results that showed increased cytotoxicity of the combination of DV and tucatinib in cell lines with a wide range of HER2 expression, which may be mechanistically attributed to elevated HER2 cell surface levels upon treatment with tucatinib. Overall, these findings provide scientific rationale to explore DV in HER2-positive and HER2-low breast cancer patients as a monotherapy or in combination with tucatinib. Citation Format: Kelsi Willis, Renee Hein, Katie Snead, Robert Thurman, Anita Kulukian. Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy and in combination with tucatinib in preclinical breast cancer models [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 PO1-04-07.

Abstract PO1-01-02: Final analysis of neoadjuvant chemotherapy with pegylated liposomal doxorubicin/cyclophosphamide followed by taxanes with full-course trastuzumab/pertuzumab for HER2-positive breast cancer: a single-arm, phase II study

Abstract Background: The optimal neoadjuvant treatment regimen for HER2-positive breast cancer remains unclear, especially regarding the use of anthracycline. We conducted a prospective phase II study to evaluate sequential neoadjuvant chemotherapy with pegylated liposomal doxorubicin (PLD)/cyclophosphamide followed by taxanes in the presence of full-course trastuzumab/pertuzumab in HER2-positive early breast cancer patients. Methods: In this single-arm, open-label, multicenter, phase II study, eligible patients with confirmed HER2-positive early breast cancer were recruited from four independent hospitals. Patients received four cycles of PLD (35 mg/m2) and cyclophosphamide (600 mg/m2), followed by four cycles of taxanes (docetaxel, 100 mg/m2 or nab-paclitaxel, 260 mg/m2), concomitant with eight cycles of trastuzumab (8 mg/kg loading dose, then 6 mg/kg) and pertuzumab (840 mg loading dose, then 420 mg) every 3 weeks. The primary endpoint was total pathological complete response (ypT0/is ypN0, tpCR). Secondary endpoints included breast pCR (bpCR), objective response rate (ORR), disease control rate, the proportion of patients requiring breast-conserving surgery, and safety. For biomarkers analysis, tumor tissues were collected at baseline and evaluated for Topoisomerase 2 Alpha (TOP2A) expression assessed prospectively with immunohistochemistry (IHC) assay by independent pathologists. Results: Between May 27, 2020 and May 11, 2022, 78 eligible patients were treated and underwent surgery, of whom 42 (53.8%) patients underwent breast-conserving surgery. After neoadjuvant therapy, 47 (60.3%, 95% CI, 48.5%-71.2%) patients achieved a tpCR in the breast and axilla. The bpCR was observed in 49 (62.8%) patients. ORRs were 76.9% (95% CI, 66.0%-85.7%) and 93.6% (95% CI, 85.7%-97.9%) after 4-cycle and 8-cycle neoadjuvant therapy, respectively. All (100%) patients achieved disease control since the end of the first cycle. No correlations between clinicopathological variables and pathological response were observed. Grade 3 or worse AEs occurred in 35 (44.9%) patients. Nine (11.5%) patients experienced asymptomatic LVEF reduction (≥10% from baseline), but all with a minimum value of &amp;gt;55%. No treatment-related surgical delay or death occurred. For biomarkers analysis, the status of TOP2A was not found to be associated with pCR or 4th-cycle ORR. Conclusions: This dual HER2-blockade plus polychemotherapy as sequential neoadjuvant regimen demonstrates promising anti-tumor activity and acceptable tolerability for patients with HER2-positive breast cancer. Citation Format: Yaping Yang, Liang Jin, Yudong li, Fengxia Gan, Nanyan Rao, Jun Zhang, Ruifa Feng, Zhenzhen Liu, Qiang Liu. Final analysis of neoadjuvant chemotherapy with pegylated liposomal doxorubicin/cyclophosphamide followed by taxanes with full-course trastuzumab/pertuzumab for HER2-positive breast cancer: a single-arm, phase II study [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 PO1-01-02.

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 PS09-09: Multiomics profiling and molecular classification refine precision treatment strategies for HER2-positive breast cancer

Abstract Background: Anti-HER2 targeted therapy has achieved a series of breakthroughs. However, the current treatment strategy regarding HER2-positive breast cancer remains indiscriminate and lacks specificity, which limits the further improvement of overall treatment response and may lead to overtreatment and extra cost for some patients. Our study aims to reveal the molecular heterogeneity of HER2-positive breast cancer to guide a more precise treatment. Patients and methods: We selected HER2-positive breast cancer patients treated at Fudan University Shanghai Cancer Center between 2013 and 2014 and conducted genomic, transcriptomic, proteomic and metabolomic profiling. We then applied a non-negative matrix factorization algorithm on transcriptomic data to obtain an unsupervised classification. And we further studied the correlation between subtypes and corresponding treatment strategies in multiple cohorts of adjuvant and neoadjuvant therapy. For clinical accessibility, we developed convolutional neural network models through deep learning algorithm based on digital pathology to identify different subtypes. Additionally, we explored novel treatment strategies using the patient-derived organoids (PDOs) models. Results: We established a novel multiomics cohort of 180 HER2- breast cancer patients and classified them into four clinically significant molecular subtypes: (1) A classical HER2-enriched (HER2-CLA, N=51) subtype characterized by strong ERBB2 signaling and remarkable sensitivity to anti-HER2-targeted therapy (pathologic complete response with dual-targeted therapy: 93%). (2) an immunomodulatory (HER2-IM, N=36) subtype characterized by an immune-activated microenvironment and excellent prognosis with current treatment (no relapse in 97% of patients with a median follow-up of 86 months). Tumors of this subtype were therefore candidates for de-escalatory treatment. (3) A luminal-like (HER2-LUM, N=55) subtype distinguished by activated estrogen receptor signaling and (4) a basal/mesenchymal-like (HER2-BM, N=38) subtype enriched in activated receptor tyrosine kinase pathways. HER2-LUM and HER2- BM showed limited benefit from anti-HER2 therapy, and thus, add-on therapies might be needed. The overall area under the curve (AUC) of the convolutional neural network model based on digital pathology for identifying different subtypes is 0.77. In the exploration of novel treatment strategies, we found in the PDO model that the HER2-LUM subtype is more sensitive to a treatment regimen combining standard (chemotherapy and targeted therapy) with subsequent endocrine therapy and CDK4/6 inhibitors compared to other subtypes. Additionally, the HER2-BM subtype demonstrated greater sensitivity to treatment with a combination of EGFR inhibitors, PDGFR inhibitors or VEGFR inhibitors. Conclusion: We uncovered a high degree of molecular heterogeneity in HER2-positive breast cancer and illustrated its impact on treatment response. More precise treatment can be given according to the characteristics of different subtypes, which may achieve good efficacy and simultaneously reduce overtreatment and extra cost. The comprehensive profiling of HER2-positive breast cancers could also serve as an important resource for further exploration. Key Words: HER2-positive breast cancer cohort; molecular classification; targeted therapy; precision treatment; de-escalatory treatment. Citation Format: Yu-Wei Li, Ding Ma, Xiang-Rong Wu, Lei-Jie Dai, Shen Zhao, Yu-Zheng Xu, Xi Jin, Xiao Yi, Ying Wang, Cai-Jin Lin, Yi-Fan Zhou, Tong Fu, Wen-Tao Yang, Ming Li, Hong Lv, Yi-Zhou Jiang, Zhi-Ming Shao. Multiomics profiling and molecular classification refine precision treatment strategies for HER2-positive 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 PS09-09.