Human Epidermal Growth Factor Receptor Research Articles

Overexpressing S100A9 ameliorates NK cell dysfunction in estrogen receptor-positive breast cancer.

Estrogen receptor (ER) positive human epidermal growth factor receptor 2 (HER2) negative breast cancer (ER+/HER2-BC) and triple-negative breast cancer (TNBC) are two distinct breast cancer molecular subtypes, especially in tumor immune microenvironment (TIME). The TIME of TNBC is considered to be more inflammatory than that of ER+/HER2-BC. Natural killer (NK) cells are innate lymphocytes that play an important role of tumor eradication in TME. However, studies focusing on the different cell states of NK cells in breast cancer subtypes are still inadequate. In this study, single-cell mRNA sequencing (scRNA-seq) and bulk mRNA sequencing data from ER+/HER2-BC and TNBC were analyzed. Key regulator of NK cell suppression in ER+/HER2-BC, S100A9, was quantified by qPCR and ELISA in MCF-7, T47D, MDA-MB-468 and MDA-MB-231 cell lines. The prognosis predictability of S100A9 and NK activation markers was evaluated by Kaplan-Meier analyses using TCGA-BRAC data. The phenotype changes of NK cells in ER+/HER2-BC after overexpressing S100A9 in cancer cells were evaluated by the production levels of IFN-gamma, perforin and granzyme B and cytotoxicity assay. By analyzing scRNA-seq data, we found that multiple genes involved in cellular stress response were upregulated in ER+/HER2-BC compared with TNBC. Moreover, TLR regulation pathway was significantly enriched using differentially expressed genes (DEGs) from comparing the transcriptome data of ER+/HER2-BC and TNBC cancer cells, and NK cell infiltration high/low groups. Among the DEGs, S100A9 was identified as a key regulator. Patients with higher expression levels of S100A9 and NK cell activation markers had better overall survival. Furthermore, we proved that overexpression of S100A9 in ER+/HER2-cells could improve cocultured NK cell function. In conclusion, the study we presented demonstrated that NK cells in ER+/HER2-BC were hypofunctional, and S100A9 was an important regulator of NK cell function in ER+BC. Our work contributes to elucidate the regulatory networks between cancer cells and NK cells and may provide theoretical basis for novel drug development.

CDK4/6 inhibitors: The Devil is in the Detail.

Update on the most recent clinical evidence on CDK4/6 inhibitors (CDK4/6i) in the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor (HER)2-negative breast cancer. Over the past decade, CDK4/6i have become part of the standard of care treatment of patients with both metastatic and high-risk early HR + /HER2- breast cancers. The three available CDK4/6i (palbociclib, ribociclib and abemaciclib) have been extensively studied in combination with endocrine therapy (ET) in metastatic breast cancer (mBC) with consistent prolongation of progression free survival; however, ribociclib has emerged as the preferred first line agent in mBC given overall survival benefit over endocrine monotherapy. In early BC, abemaciclib is the only currently approved agent while ribociclib has early positive clinical trial data. Toxicities and financial burden limit the use of CDK4/6i in all patients and resource-poor settings, and optimal timing of their use in mBC remains unclear. There is considerable evidence for the use of CDK4/6i in metastatic and early HR + /HER2- breast cancer, but knowledge gaps remain, and further research is necessary to better define their optimal use.

Incidence and survival of primary metastatic breast cancer in Denmark; implication of breast cancer screening, classification, and staging practice.

Primary metastatic breast cancer (pMBC) accounts for 5-10% of annual breast cancers with a median survival of 3-4 years, varying among subtypes. In Denmark, the incidence of breast cancer increased until 2010, followed by a stabilisation. Several factors influencing pMBC incidence and survival, including screening prevalence, staging methods, and classification standards, remain pivotal but inadequately documented. This retrospective observational study involving pMBC patients diagnosed between 2000 and 2020 encompassed all Danish oncology departments. Data from the Danish Breast Cancer Group database and the National Patient Register included diagnosis specifics, demographics, treatment, and follow-up. Between 2000 and 2020, 3,272 patients were diagnosed with pMBC, a rise from 355 patients in 2000-2004 to 1,323 patients in 2015-2020. The increase was particularly observed in patients aged 70 years or older. Changes in tumour subtypes were observed, notably with a rise in human epidermal growth factor receptor 2 (HER2)-positive cases but a steady distribution of estrogen receptor (ER) status. Diagnostic practices changed over the two decades, with 6% evaluated with PET/CT (positron emission tomography-computed tomography) or CT (computed tomography) with a bone evaluation in 2000-2004 and 65% in 2015-2020. Overall survival (OS) improved from 23 months in 2000-2004 to 33 months in 2015-2020. In patients with ER-positive and HER2-positive disease, the multivariable model showed improved survival by year of diagnosis, and further, patients with ER-negative/HER2-negative disease fared worse the first 2 years after diagnosis. Our study delineates changes in the treatment and survival of pMBC over two decades. Stage migration, screening introduction, and changes in registration practice, however, prevent a valid assessment of a possible causal relationship.

Loss of copy numbers of retrotransposons (HERVK) on chromosome 7p11.2 impacts EGFR (Epidermal Growth Factor Receptor)-induced phenotypes for platinum sensitivity and long-term survival in ovarian cancer-A study from the OVCAD consortium.

We analyzed variations in the epidermal growth factor receptor (EGFR) gene and 5'-upstream region to identify potential molecular predictors of treatment response in primary epithelial ovarian cancer. Tumor tissues collected during debulking surgery from the prospective multicenter OVCAD study were investigated. Copy number variations in the human endogenous retrovirus sequence human endogenous retrovirus K9 (HERVK9) and EGFR Exons 7 and 9, as well as repeat length and loss of heterozygosity of polymorphic CA-SSR I and relative EGFR mRNA expression were determined quantitatively. At least one EGFR variation was observed in 94% of the patients. Among the 30 combinations of variations discovered, enhanced platinum sensitivity (n = 151) was found dominantly with HERVK9 haploidy and Exon 7 tetraploidy, overrepresented among patients with survival ≥120 months (24/29, p = .0212). EGFR overexpression (≥80 percentile) was significantly less likely in the responders (17% vs. 32%, p = .044). Multivariate Cox regression analysis, including age, FIGO stage, and grade, indicated that the patients' subgroup was prognostically significant for CA-SSR I repeat length <18 CA for both alleles (HR 0.276, 95% confidence interval 0.109-0.655, p = .001). Although EGFR variations occur in ovarian cancer, the mRNA levels remain low compared to other EGFR-mutated cancers. Notably, the inherited length of the CA-SSR I repeat, HERVK9 haploidy, and Exon 7 tetraploidy conferred three times higher odds ratio to survive for more than 10 years under therapy. This may add value in guiding therapies if determined during follow-up in circulating tumor cells or circulating tumor DNA and offers HERVK9 as a potential therapeutic target.

Analyzing Neoadjuvant Chemotherapy Effects in HER2-Low Breast Cancer: Real World Data.

Neoadjuvant chemotherapy (NAC) can be used as upfront therapy in aggressive breast cancer (BC). human epidermal growth factor receptor 2 (HER2)-low BC, defined as tumors scoring +1 or +2 on immunohistochemistry without HER2 gene amplification by in situ hybridization, lacks information on real-world data (RWD) outcomes, especially in the NAC setting. This subgroup, which does not reach the HER2 positive criteria due to its lower receptor expression, represents a distinct clinical category potentially requiring tailored therapeutic approaches. The objective of this study is to characterize patients with BC with HER2-low status who received NAC in a Brazilian public reference center for female tumors and key outcomes such as pathological complete response (pCR), overall survival (OS), and metastasis-free survival (MFS). A retrospective cohort study based on a large BC database from a reference cancer center in Brazil. Patients with BC that received NAC, diagnosed between 2011 and 2020, were included if they presented HER2-low status (defined as tumors scoring +1 or +2 on immunohistochemistry without HER2 gene amplification by in situ hybridization) and had complete data on outcomes. Clinical and demographicdata were collected, such as age, menopausal status, Ki-67, hormone receptorexpression and others. Key outcomes from the study comprised pCR (defined as ypT0/TIs/ypN0), overall survival, and metastasis-free survival (MFS). Survival analyses were conducted through the semiparametric Kaplan-Meier method to assess OS and MFS by pCR status, considering BC diagnosis as the index date. Overall, 297 patients were eligible and 141 were included in the study after matching the HER2-low definition. The pCR was seen in 18 out of 141 patients (12.7%). The median overall survival was 8.2 years, and the median MFS was 2.7 years. The OS of pCR was 83.4% and non-pCR was 58.1%; the DFS of pCR was 55.5% and non-pCR 40.6%. This study gives updated insights on pCR, OS, and MFS in women with HER2-low BC exposed to NAC.

Radiological Features for Predicting the Status of CD8-Positive Lymphocytes in HER2 Positive Breast Cancer.

The level of tumor-infiltrating lymphocytes (TILs) in human epidermal growth factor receptor type 2 (HER2)-positive breast cancer (BC) is positively correlated with pathological complete response. To investigate the relationship between ultrasound (US) and magnetic resonance imaging (MRI) features and the level of CD8-positive TILs (CD8+-TILs) in patients with HER2-positive BC. Retrospective cohort study. This retrospective study included 155 consecutive women with HER2-positive BC. Patients were divided into two groups: CD8+-TILlow (< 35%) and CD8+-TILhigh (≥ 35%) groups. US and MRI features were evaluated using the BI-RADS lexicon, and the apparent diffusion coefficient (ADC) value was calculated using RadiAnt software. Univariate and multivariate analyses revealed the optimal US and MRI features for predicting CD8+-TIL levels. Receiver operating characteristic analysis and the Delong test were used to compare the diagnostic performance of US and MRI features. Furthermore, implementing a nomogram will increase clinical utility. Univariate analysis of US features showed significant differences in shape, orientation, and posterior echo between the two groups; however, there were no significant differences in margins, internal echo, and microcalcification. Multifactorial analysis revealed that shape, orientation, and posterior echo were independent risk factors, with odds ratios of 11.62, 2.70, and 0.16, respectively. In terms of MRI features, ADC was an independent predictor of CD8+-TIL levels. These three US features and the ADC performed well, with area under the curve (AUC) values of 0.802 and 0.705, respectively. The combination of US and ADC values had higher predictive efficacy (AUC = 0.888) than either US or ADC alone (p = 0.009, US_ADC vs. US; p < 0.001, US_ADC vs. ADC). US features (shape, orientation, and posterior echo) and ADC value may be a valuable tool for estimating CD8+-TIL levels in HER2-positive BC. The nomogram may help clinicians in making decisions.

HER2-targeting CAR-T cells show highly efficient anti-tumor activity against glioblastoma both in vitro and in vivo.

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor in adults. Current treatment options for GBM include surgical resection, radiation, and chemotherapy, which predominantly slow cancer growth and reduce symptoms, resulting in a 5-year survival rate of no more than 10%. Chimeric antigen receptor (CAR) T-cell therapy is a new class of cellular immunotherapy that has made great progress in treating malignant tumors. Human epidermal growth factor receptor 2 (HER2) is overexpressed in GBM and may provide a potential therapeutic target for GBM treatment. In this study, we constructed third-generation CAR-T cells targeting the HER2 antigen in GBM. HER2-CAR-T cells showed effective anti-tumor activity both in vitro and in vivo. Furthermore, HER2-specific CAR-T cells exhibited strong cytotoxicity and cytokine-secreting abilities against GBM cells in vitro. Anti-HER2 CAR-T cells also exhibited increased cytotoxicity with increasing effector-to-target ratios. Anti-HER2 CAR-T cells delivered via peritumoral injection successfully stunted tumor progression in vivo. Moreover, peritumoral intravenous administration of anti-HER2 CAR-T cells resulted in therapeutic improvement against GBM cells compared with intravenous administration. In conclusion, our study shows that HER2 CAR-T cells represent an emerging immunotherapy for treating GBM.

Abstract PO4-02-14: Parity and age first full term pregnancy affects the odds of different breast cancer subtypes defined by estrogen receptor and human epidermal growth factor receptor-2

Abstract Background: A rising trend in the incidence of estrogen receptor (ER)-positive subtype over time is observed in several high-income countries, while the incidence of ER-negative subtype is decreasing in some areas. It has been found that decreased parity and late age at 1st full-term pregnancy (FTP1) can increase the risk of breast cancer (BC). This study aims at investigating the association between two reproductive factors, parity and FTP1, and the odds of BC subtypes in premenopausal and postmenopausal patients. Patients and method: This study included patients diagnosed with early-stage BC after the age of 34, who were treated in UZ Leuven between January 2000 and November 2020. The patients were classified into four subtypes defined by ER and human epidermal growth factor receptor-2 (HER2). ER positivity was defined as &amp;gt;1% of cells staining positive while HER2 positivity was based on fluorescence in situ hybridization (FISH) testing of samples with immunohistochemistry score of 2+ or 3+. Baseline-category logit models with subtype as the response (ER+/HER2- as the baseline) and adjusted for age at diagnosis and BMI, were performed for premenopausal and postmenopausal patients separately. First, we exclude nulliparous patients. Parity (1-2 or ≥3) and FTP1 (continuous) were included in the models as the covariates of interest in the first model. To evaluate the effects of reproductive patterns compared to nulliparity, a new variable reproductive pattern was created by taking intersection of parity groups and FTP1 groups (&amp;lt; 27, ≥27). Reproductive pattern was set as the covariate of interest in the second model. Result: After imputing the missing values, we included 9606 patients in the study. 8125 of them were parous. In parous patients, high FTP1 was associated with low odds of ER-/HER2- BC relative to ER+/HER2- BC for both premenopausal and postmenopausal patients (table 1). In postmenopausal patients, low parity was associated with low odds of ER-/HER2- BC and high odds of ER+/HER2+ BC relative to ER+/HER2- BC. There was no evidence that parity affects the odds of subtypes in premenopausal patients. When investigating the effect of different reproductive patterns compared to nulliparity on the odds of subtypes, there was no evidence that reproductive patterns will affect the odds of subtypes in premenopausal patients. Postmenopausal patients who had FTP1 before 27 years old and had at least three children tended to have higher odds of ER-/HER2- BC relative to ER+/HER2- BC compared to nulliparous patients. Conclusion: In parous patients, increased FTP1 was associated with reduced odds of ER-/HER2- relative to ER+/HER2- BC. In postmenopausal patients, patients with at least three children tended to have low odds of ER-/HER2- BC and high odds of ER+/HER2+ BC relative to ER+/HER2- BC. When compared to nulliparity, the combination of having at least three children and having the first child before 27 years old increased the odds of ER-/HER2- BC relative to ER+/HER2- BC in postmenopausal patients. Table 1 Effect of FTP1, parity on subtype odds Menopause Subtype Effect Odds ratio (95%CI) p-value pre ER-/HER2- FTP1 (continuous) 0.960 (0.935, 0.985) 0.0021 post 0.969 (0.948, 0.990) 0.0047 pre ER-/HER2+ 0.992 (0.952, 1.034) 0.7166 post 1.005 (0.977, 1.034) 0.7081 pre ER+/HER2+ 0.976 (0.949, 1.004) 0.0962 post 1.015 (0.992, 1.039) 0.1969 pre ER-/HER2- Parity 1-2 vs ≥3 1.194 (0.899, 1.585) 0.2200 post 0.784 (0.648, 0.949) 0.0124 pre ER-/HER2+ 1.152 (0.723, 1.834) 0.5521 post 0.896 (0.684, 1.173) 0.4228 pre ER+/HER2+ 1.080 (0.795, 1.469) 0.6220 post 1.300 (1.022, 1.654) 0.0329 The baseline category is ER+/HER2- subtype Effect of age at first full-term pregnancy and parity on subtype odds Citation Format: Zhao Liu, Jiumeng Zhang, Karen Van Baelen, Maja Vangoitsenhoven, Hans Wildiers, Adelheid Soubry, Patrick Neven. Parity and age first full term pregnancy affects the odds of different breast cancer subtypes defined by estrogen receptor and human epidermal growth factor receptor-2 [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 PO4-02-14.

Abstract PO2-02-07: Clinicopathological Features and Prognostic Role of HER2 Low in Early Breast Cancer: A real world study

Abstract Background: The definition of human epidermal growth factor receptor-2(HER2) low was proposed with the development of T-DXd, a novel antibody-drug conjugate (ADCs) targeting HER2 in the field of breast cancer (BC) treatments. However, whether HER2 low is a distinct subgroup is still an ongoing debate with mixed results. Current retrospective studies focused on HER2 low concentrated more on metastatic BC, less was known in early BC. The retrospective study was conducted based on HER2 low early BC to comprehensively analyze its clinicopathological features and prognostic roles compared with HER2 IHC0. Methods: This single institution retrospective study enrolled 999 early stage (stage I through III) HER2 negative invasive BC patients diagnosed at Chinese PLA General Hospital from January 2010 to December 2015. Tumors with HER2 immunohistochemical (IHC) score of 1+ or 2+ with negative in situ hybridization assay were defined as HER2 low. Clinicopathological characteristics s and survival outcomes including disease-free survival (DFS) and overall survival (OS) were compared between HER2 IHC0 and HER2 low groups. The correlations between HER2 expression and estrogen receptor (ER) status were determined by Mantel-Haenszel χ2 test. Cohen’s kappa coefficient (k) was adopted to evaluate the concordance between HER2 expression on primary tumors and matched biopsies. Results: 999 patients were eligible for inclusion criteria, among which the percentages of HER2 low in the whole cohort, HR positive group and HR negative group were 83.6%, 86.54%, 72.14% respectively. It was observed the presence of a significant higher proportion of ER level &amp;gt; 10% (p &amp;lt; 0.001), PgR positive (p &amp;lt; 0.001) and more patients who received endocrine therapy (p = 0.002). In HR positive group, clinicopathological features were balanced between HER2 IHC0 and HER2 low. In HR negative group, HER2 low manifested a higher proportion of invasive ductal type (p = 0.016) compared with HER2 IHC0. Survival analysis showed a significantly longer OS in HER2 low BC than HER2 IHC0. (HR: 0.458, 95%CI: 0.262-0.800, p = 0.0005). Nevertheless, the independent role was not reached in DFS. When stratified by HR status, patients with HER2 low in HR positive group demonstrated a longer OS than HER2 IHC0 (HR: 0.55, 95%CI: 0.273-1.105, p = 0.0385). The same trend was observed in HR negative group (HR: 0.385, 95%CI: 0.158-0.939, p = 0.0132). Neither the HR positive group nor the HR negative group achieved significant DFS. Besides, a positive correlation was observed between ER status and the rate of HER2 low (Mantel-Haenszel c2 test, p &amp;lt; 0.001, Pearson’s R = 0.159, P &amp;lt; 0.001). No regularity of survival differences between HER2 IHC0 and HER2 low was found in each ER level in the exploratory study. Finally, 119 patients who developed relapsed or metastatic disease were identified, with the most prevalent metastatic site being bone (31.1%), following by lung (16.80%) and lymph node (13.44%). Among 52 patients with matched biopsy samples, dynamic changes of HER2 IHC status were confirmed in both primary and relapsed statuses, with an discordance rate of 28.84% (K = 0.194, 95%CI: 0.168-0.219). conclusion: HER2 low expression breast cancer may not be regarded as a unique BC group in this real-world population due to similar clinicopathological features and prognostic roles especially in hormone-receptor positive cases. ER level was positively correlated with the rate of HER2 low population. Overall, whether HER2 low is a distinct subgroup remains to be supported and validated by more data both in clinical and molecular levels. Key words: HER2 low; Breast cancer; Clinicopathological Features; Prognosis; Molecular type Clinicopathological Features and Prognostic Role of HER2 Low in Early Breast Cancer: A real world study Citation Format: Ziqing Kong, Weihong Zhao. Clinicopathological Features and Prognostic Role of HER2 Low in Early Breast Cancer: 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 PO2-02-07.

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 PO2-04-12: From Clinical Trials to Clinical Practice; Real World Clinical Outcomes of Patients Treated with Ribociclib in Combination with Aromatase Inhibitors or Fulvestrant for HR-Positive, HER2- Negative Metastatic Breast Cancer

Abstract Background: Cyclin-dependent kinase (CDK) 4/6 inhibitors have revolutionized the treatment landscape of hormone receptor-positive (HR+), human epidermal growth factor receptor-2 (HER2)-negative metastatic breast cancer (MBC), with an impressive efficacy and safety profile. Here we report real-world clinical outcomes and toxicity data in patients treated at a tertiary care cancer center. Methods: The study is a retrospective analysis of individual patients’ data. All consecutive patients with HR+ and HER2-negative MBC, treated at our institution with ribociclib plus aromatase inhibitors (AI) or fulvestrant, between June 2017 and May 2020 were reviewed. Data were collected from patients’ electronic medical records. Progression free survival (PFS) was defined as the time from treatment initiation with CDK4/6i until the first documented progression, death from any cause or last follow-up, whichever occurred first. The Overall survival (OS) was defined as the time from treatment initiation with CDK4/6i until the date of death from any cause, or last follow-up. Results: A total of 305 patients, median age 49 (22-87) years were enrolled. Although bone metastasis was reported in 241 (79.0%) patients, bone-only metastasis was identified in 64 (20.9%). Visceral metastasis in the liver and lungs were reported in 22.0% and 25.9 % of patients, respectively. CDK4/6i combined with AI were used in first-line setting in 195 (63.9%) patients and with fulvestrant as a second line (20.7%) or beyond (15.4%). Dose reduction was required in 44 (14.14%) patients, mostly because of neutropenia (n=38, 12.5%) and abnormal liver enzymes (n=12, 3.9%), while 11 (3.6%) discontinued treatment, mostly due cardiac toxicities. Nevertheless, there were no deaths due to toxicity. Patients were followed up for a median of 31.1 months. Overall response rate (ORR) was 51.4% and median PFS, irrespective of the line of therapy, was 19.3 (17.6-23.3) months. PFS was longer in first-line setting; 23.1 (19.7-NR) months compared to 13.9 (10.2-17.6) months in second-line or beyond, p&amp;lt; 0 .0001, and when combined with AI compared to fulvestrant; 28.6 (17.8-23.1) months versus 9.1 (4.4-NR) months, p=0.0001, and in those with bone-only metastasis; 23.1 (19.5-NR) months versus 17.3 (12.2-18.9) months for patients with visceral metastasis, p=0.0008. The median OS was not reached. Conclusions: Despite enrolling sicker patients, and outside the stringent clinical trials settings, our treatment outcomes, in real world settings, are comparable to those reported in major clinical trials, including MONALEESA-2, MONALEESA-3 and MONALEESA-7. Citation Format: Baha' Sharaf, Faris Tamimi, Sarah Edaily, Osama Salama, Hazem Abdulelah, Anas Zayed, Mahmoud Abunasser, Hala Abu-Fares, Hikmat Abdel-Razeq. From Clinical Trials to Clinical Practice; Real World Clinical Outcomes of Patients Treated with Ribociclib in Combination with Aromatase Inhibitors or Fulvestrant for HR-Positive, HER2- Negative 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 PO2-04-12.

Abstract PO3-08-09: Unique molecular signatures of germline mutations in low expression of human epidermal growth factor receptor 2 (HER2) breast cancer

Abstract Background: Overexpression of human epidermal growth factor receptor 2 (HER2) in breast cancer (BC) is associated with lower survival and higher risk of disease recurrence. A new subtype of HER2-low BC which has been proposed from several studies demonstrates that HER2-low patients have distinct somatically genetic alterations and clinical outcomes. We have previously reported that HER2-low BC had distinct clinical and somatic mutational feature compared with HER2-zero and HER2-high tumors. We have therefore extended studies by comparing germline mutation expression among these HER2 subgroups. Methods: 530 Chinese women with BC were enrolled in a prospective protocol between May 2021 to March 2023 at Guangdong Provincial People's Hospital. Genomics data was generated from a gene panel that surveys 102 tumor mutations. Germline variants were classified into pathogenic (P), likely pathogenic (LP), variant of uncertain significance (VUS), likely benign (LB) and benign (B) groups according to the ACMG/AMP Standards and Guidelines. The cohort was divided into three groups based on HER2 status as HER2-zero (n = 107), HER2-low (n = 259), and HER2-high (n = 127) according to immunohistochemistry and/or fluorescence in situ hybridization results. Results: The most common mutated genes were ATM, FANCD2, ATR, BRACA2, RECQL4 and APC. A total of 71 pathogenic or likely pathogenic (P/LP) mutations were identified in 25 cancer susceptibility genes from 64 patients (12.16%). The most frequent mutated P/LP genes are BRCA2, BRCA1, PALB2, PMS2, MUTYH and PTEN in the HER2-low group; BRCA2, BRCA1 and PALB2 in the HER2-zero cohort; Interestingly, among the nine HER2-high patients, we detected unique P/LP genes in each sample including MRE11, FANCM, ATM, FLCN, NTRK1, TP53, BRCA1, CHEKE2 and FANCA. In addition to P/LP mutations, 751 variants of uncertain significance (VUS) in 95 cancer susceptibility genes were also detected in 361 patients (68.11%). The most frequent mutated VUS mutations occurred genes are FANCD2, ATM, RECQL4, RAD54B and ATR in HER2-low group; ATM, FANCA, POLE, MSH2 and FANCD2 in HER2-zero cohort; and ATM, BRCA2, RECQL4, POLE, FANCI and FANCM for HER2-high patients. Most of mutated genes were homologous recombination repair (HRR) or DNA damage repair (DDR) pathway related genes. Several genes were differentially altered across HER2 subgroups, including the mutation frequency of the BMPR1A (p=0.0344), MSH2 (p=0.0103), and RAD51C (p=0.0336) genes that were significantly higher in HER2-zero group. It’s worth noting that RAD51C was only mutated in HER2-zero subgroup. BMPR1A and MSH2 were also mutated in HER2-low patients. Differentially mutated genes in specific HER2 subgroups may contribute to better research and choice of future therapeutic approaches. In 115 patients who received neoadjuvant therapy and 84 of them were evaluable for pathological response data, HER2-low patients had lower pathological complete response (pCR) rates than HER2-zero and HER2-high subgroups (p=0.0008). In particular, DDR pathway gene ERCC1 have significantly higher mutation frequency in pCR patients (p=0.0115). Conclusion: HER2-low BC patients have distinct germline mutational signatures and differential clinical outcomes under neoadjuvant systemic therapy. These results have provided additional evidence that HER2-low patients comprise a fourth subtype of BC that needs to be accounted for separately in terms of clinical treatment and outcome reporting. Keywords: breast cancer, germline mutations, human epidermal growth factor receptor 2 (HER2), HER2-low, targeted therapy, next-generation sequencing Table 1. List of most frequent mutated genes in HER2-zero, HER2-low and HER2-high groups Citation Format: Ning Liao, Weiqi Zhang, Liangqiu Liu, Wendy Wu, Siqi Wang, Li Cao, Jianguo Lai, Xueying Zhang, Airong Yang, Yulei Wang, Cheukfai Li, Guochun Zhang, Chongyang Ren, Lingzhu Wen. Unique molecular signatures of germline mutations in low expression of human epidermal growth factor receptor 2 (HER2) 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 PO3-08-09.

Abstract PO1-06-03: Efficacy of First-line Treatments for Hormone Receptor-positive, Human Epidermal Growth Factor Receptor 2-positive Metastatic Breast Cancer: A Systematic Literature Review and Network Meta-analysis Feasibility Assessment

Abstract Background: A comprehensive summary of clinical evidence for first-line (1L) treatments for hormone receptor-positive, human epidermal growth factor receptor 2-positive (HR+/HER2+) advanced or metastatic breast cancer (mBC) is needed to understand which treatments have been evaluated and the outcomes associated with different treatments. Understanding the available clinical evidence for HR+/HER2+ mBC 1L treatments can also inform the feasibility of network meta-analyses (NMAs) to estimate relative treatment effects where head-to-head trials are not available. The objective was to prepare a systematic summary of clinical trials of 1L treatments for HR+/HER2+ mBC and assess the feasibility of NMAs for key efficacy outcomes. Methods: A systematic literature review (SLR) was conducted per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Clinical trials evaluating 1L treatments for adults with HR+/HER2+ mBC published between January 2000 and January 2023 were identified via predefined searches of databases (Embase, MEDLINE, Cochrane Library), relevant congress proceedings, and ClinicalTrials.gov (updating a previous SLR covering January 2000 to December 2020). Study design characteristics, patient characteristics, and efficacy outcomes were extracted from identified trials. An NMA feasibility assessment that considered network connectivity and cross-study heterogeneity was conducted for four efficacy outcomes of interest: progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and clinical benefit rate (CBR). Results: After screening, 37 records reporting on 23 unique studies (11 randomized controlled trials [RCTs] and 12 single-arm trials; 35 study arms in total) were selected. Included trials were mostly phase II or phase III multi-country studies that evaluated a HR+ or HER2+ population, with outcomes being reported for the subgroup of patients with the HR+/HER2+ subtype. Treatments evaluated included one or two anti-HER2 therapies (AHTs) + endocrine therapy (ET) (5/35 study arms), AHTs + chemotherapy (CT) (20/35), AHTs + ET + CT (2/35), AHTs alone (5/35), and ET alone (3/35). For HR+/HER2+ patients, PFS and OS were reported by 17/23 and 10/23 studies, respectively. Reported median PFS and OS ranged from 2.4-23.7 months and 23.9-66.7 months, respectively. Among the 11 included RCTs, hazard ratios and/or Kaplan-Meier curves, which were considered a requirement for NMAs for time to event outcomes, were reported for PFS and OS by 9 and 6 studies, respectively. Among these studies, reported median PFS and OS ranged from 2.4-19.2 months and 23.9-57.9 months, respectively. For HR+/HER2+ patients, ORR and CBR were reported by 13/23 and 6/23 studies, respectively. Assuming all CTs could be considered equivalent treatments and all ETs could be considered equivalent treatments, NMAs involving networks of 9, 6, 6, and 3 treatments were feasible for PFS, OS, ORR, and CBR, respectively. Some patient characteristics including time since mBC diagnosis and proportion with bone metastases were not reported consistently across trials. However, included studies were broadly comparable based on study design characteristics, outcome definitions and other reported patient characteristics such as age and Eastern Cooperative Oncology Group performance status. Conclusion: Clinical trials in 1L HR+/HER2+ mBC have evaluated various combinations of AHTs, CTs, and ETs, with most study arms being AHTs + CT. Although efficacy outcomes of interest were not consistently reported across trials, NMAs were found to be feasible for PFS, OS, ORR, and CBR based on available data. Citation Format: Priyanka Sharma, Chau Dang, Christopher Drudge, Amrita Debnath, Manvir Rai, Eric Gauthier, Edward Broughton. Efficacy of First-line Treatments for Hormone Receptor-positive, Human Epidermal Growth Factor Receptor 2-positive Metastatic Breast Cancer: A Systematic Literature Review and Network Meta-analysis Feasibility 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 PO1-06-03.

Abstract PO4-04-12: A Phase 1b/2 study of palazestrant (OP-1250) in combination with ribociclib or alpelisib in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative, advanced and/or metastatic breast cancer

Abstract Background: Endocrine therapy (ET) when administered with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors has improved outcomes in patients (pts) with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (BC) or metastatic breast cancer (MBC) and is the current standard of care for first-line treatment. Addition of the PIK3 inhibitor alpelisib to ET significantly improved progression-free survival in pts with PIK3CA-mutated, ER-positive, HER2-negative MBC, and alpelisib + fulvestrant is the standard of care for second or later-line treatment. Most pts will acquire resistance to ET, with mutations in ESR1 constituting the most common mechanism of resistance. Palazestrant (OP-1250) is a small molecule oral complete ER antagonist (CERAN) and selective ER degrader (SERD) that binds the ligand binding domain of ER and completely blocks ER-driven transcriptional activity in both wild-type (ESR1-wt) and mutant (ESR1-mut) forms of ER. In preclinical studies, palazestrant in combination with ribociclib demonstrated activity in both ESR1-wt and ESR1-mut xenograft models and showed efficacy in brain metastasis xenograft models. In a Phase 1/2 monotherapy study in pts with ER-positive, HER2-negative MBC, palazestrant was well tolerated with demonstrated antitumor efficacy and favorable pharmacokinetics (PK) supporting once a day (qd) dosing at the recommended Phase 2 dose (RP2D) of 120 mg. The aim of this study is to evaluate the safety, PK, and antitumor activity of palazestrant + ribociclib or alpelisib in pts with ER-positive, HER2-negative advanced BC or MBC. Methods: Eligible pts have evaluable ER-positive, HER2-negative advanced BC or MBC; ≤2 prior ETs (prior CDK4/6 inhibitors allowed); and ≤1 prior line of chemotherapy. In the alpelisib arm, pts must have a PIK3CA mutation in the tumor or ctDNA. Patients are administered oral palazestrant at escalating doses of 30, 60, and 120 mg qd in combination with the approved dose of oral ribociclib (600 mg qd; days 1–21 of 28-day cycle) or approved dose of oral alpelisib (300 mg qd) in a 3+3 design to identify the RP2D. The dose-expansion part will assess additional safety and PK parameters and the antitumor activity of palazestrant in combination with ribociclib or alpelisib (NCT05508906). Results: As of June 15, 2023, 10 pts have received 30 mg and 60 mg doses of palazestrant in combination with ribociclib (n=6) or alpelisib (n=4). No dose-limiting toxicities have been observed. After administration in the first two combination dose levels of 30 and 60 mg, palazestrant exposure was consistent with monotherapy administration; exposure data show no drug–drug interactions (DDI) when compared to published exposure parameters. Most reported treatment-emergent adverse events (TEAEs) were grade 1 or 2 and consistent with the known safety profiles of all 3 drugs. In the ribociclib arm, the TEAEs occurring in ≥2 pts included grade 1 nausea (n=4), grade 1 constipation (n=2), and neutropenia (grade 2, n=1; grade 3, n=3). For the 3 pts in the 30 mg palazestrant + alpelisib cohort, the only TEAE occurring in ≥2 pts was grade 1 diarrhea. One pt had grade 1 hyperglycemia. Conclusions: In this ongoing study, palazestrant in combination with ribociclib or alpelisib was well tolerated, and enrollment to the palazestrant 120 mg dose with ribociclib or alpelisib is ongoing. No new safety signals were observed for the 3 drugs, and no clinically significant DDIs were observed between palazestrant and ribociclib or alpelisib at the doses evaluated. Exposure of each drug was consistent with observed monotherapy exposure levels. Updated data will be presented. Citation Format: Virginia Borges, Carlos Alemany, Nancy Lin, Sara Nunnery, Cynthia Ma, Margaret Tonda, Morena Shaw, Arlene Chan. A Phase 1b/2 study of palazestrant (OP-1250) in combination with ribociclib or alpelisib in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative, advanced and/or 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 PO4-04-12.

Abstract PO4-02-13: Parity and age first full term pregnancy affects the age of breast cancer diagnosis in breast cancer subtypes defined by estrogen receptor and human epidermal growth factor receptor 2

Abstract Background: Reproductive factors like parity and age at first full term pregnancy (FTP1) are found to have an impact on the occurrence of breast cancer (BC) in many epidemiological studies. Importantly, since the 70s, an ongoing trend to postpone FTP1 and have less children is observed. Additionally, there is an increasing trend for breast cancer incidence in young women in the past several decades, which may match the changing exposures to reproductive factors over time. To our knowledge, few studies focus on the association between parity, FTP1 and the age of breast cancer diagnosis. In this study, we aimed at studying the association between age at breast cancer diagnosis and reproductive factors (parity and FTP1) in each of the four breast cancer subtypes defined by estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2). Patients and method: We considered patients who were &amp;gt;34 years old and were diagnosed and/or treated for early BC in University Hospitals Leuven between January 2000 and November 2020. Patient and tumor characteristics were extracted from the patient files. Missing values were filled in by multiple imputation. A linear mixed model with birth cohorts as random effects was built for premenopausal and postmenopausal patients separately to investigate the association between two reproductive factors (parity and age at first full term pregnancy) and age at diagnosis in each of four breast cancer subtypes defined by ER and HER2. ER positivity was defined as &amp;gt;1% of cells staining positive and reflex fluorescence in situ hybridization (FISH) testing was performed for samples that immunohistochemically (IHC) stained for HER2 with IHC score of 2+ or 3+. Parous women are classified into low parity (1 or 2 children) and high parity (≥ 3 children) and FTP1 was divided into &amp;lt; or ≥ 27 years of age. BMI was considered a possible confounder and was corrected for. We first excluded nulliparous people and compared the mean ages at diagnosis in different parity groups and FTP1 groups separately. We created new variable reproductive patterns by taking intersection of parity categories and FTP1 categories. Then the mean ages at diagnosis in parous groups could be compared with the mean age at diagnosis in nulliparous patients. Step down Bonferroni procedure is applied to correct for multiple comparisons. Result: 3039 premenopausal patients and 6569 postmenopausal patients at breast cancer diagnosis were included in the study. Patients with early age at FTP1 have older age at diagnosis in case of ER+HER2+ BC in both premenopausal and postmenopausal group as compared to patients with late FTP1 (Table 1). For premenopausal patients with ER-HER2+, early age at FTP1 was associated with older age at diagnosis in comparison to late age at FTP1. Premenopausal patients with ER+HER2- BC that had low parity and late FTP1 were diagnosed 0.66 years later than nulliparous patients (p= 0,01). Conclusion: In both premenopausal and postmenopausal parous patients with early FTP1, an older age at diagnosis was observed in HER2+ cases only. When compared to nulliparous patients, the combination of low parity and late FTP1 was associated with older age at diagnosis for premenopausal patients with ER+ HER2- BC. Table 1 Differences in mean age at diagnosis between FTP1 groups in parous patients Menopause Subtype Comparison Estimate (difference in mean age at diagnosis) p-value pre ER+HER2+ &amp;lt;27 vs &amp;gt;=27 1,2030 0,0045 ER+HER2- &amp;lt;27 vs &amp;gt;=27 -0,0548 0,7468 ER-HER2+ &amp;lt;27 vs &amp;gt;=27 1,3519 0,0334 ER-HER2- &amp;lt;27 vs &amp;gt;=27 0,4023 0,3326 post ER+HER2+ &amp;lt;27 vs &amp;gt;=27 1,1764 0,0175 ER+HER2- &amp;lt;27 vs &amp;gt;=27 0,0743 0,7069 ER-HER2+ &amp;lt;27 vs &amp;gt;=27 -0,3750 0,6023 ER-HER2- &amp;lt;27 vs &amp;gt;=27 0,3862 0,3815 Citation Format: Jiumeng Zhang, Zhao Liu, Karen Van Baelen, Maja Vangoitsenhoven, Hans Wildiers, Adelheid Soubry, Patrick Neven. Parity and age first full term pregnancy affects the age of breast cancer diagnosis in breast cancer subtypes defined by estrogen receptor and human epidermal growth factor receptor 2 [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 PO4-02-13.

Abstract PS08-04: Multicenter retrospective cohort study of the sequential use of the antibody-drug conjugates (ADCs) trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) in patients with HER2-low metastatic breast cancer (MBC)

Abstract Introduction. T-DXd is FDA-approved for patients (pts) with hormone receptor positive (HR+) or HR- HER2-low (IHC 1+ or 2+, ISH-) MBC and SG is FDA-approved for pts with HR+/HER2- and triple negative MBC. However, several outstanding questions impact the use of these drugs in clinic, including: 1) what is the efficacy and safety of these agents in real-world populations with diverse pt characteristics not well represented in the pivotal phase III trials, and 2) what is the impact of sequential treatment with ADCs on the efficacy and safety of these agents. Methods. In this multicenter retrospective cohort study, we identified pts with HR+/HER2-low and HR-/HER2-low MBC who had received both T-DXd and SG monotherapy (in either order, with or without intervening therapies) treated at 5 academic centers between 2020-2023. Pts received treatment per standard of care or on a clinical trial with ADC monotherapy. We describe pt demographic and clinical characteristics, treatment history, key safety parameters, and response and survival data by HR+ status and ADC sequence order. Results. Sixty pts with MBC treated sequentially with T-DXd and SG were included in this analysis, including 45 pts with HR+/HER2-low MBC (75.0%) and 15 pts with HR-/HER2-low MBC (25.0%). Most pts were female (n=59; 98.3%), non-Hispanic (n=49, 81.7%), and white (n=43, 71.7%). Median age at start of ADC #1 was 56.6 years (range 23-82). Prior to treatment with ADC #1, most pts had visceral disease (n=45, 75.0%) and 16 (26.7%) had central nervous system metastases. Among pts with HR+/HER2-low MBC, median time from MBC diagnosis to treatment with ADC #1 was 49.0 months, with 4 median lines of prior therapy in the metastatic setting (2 endocrine, 2 chemo). Approximately half of the HR+ pts received T-DXd prior to SG (n=22, 48.9%; median 3.0 prior lines of therapy for MBC, range 1-9) while the other half received SG prior to T-DXd (n=23, 51.1%; median 4.5 prior lines of therapy for MBC, range 1-10). 44% (n=20) received an intervening therapy between ADCs. For HR+ pts who received T-DXd prior to SG, response and survival data is as follows for T-DXd and SG respectively: Overall response rate (ORR) [54.5% and 21.1%], time to next treatment (TTNT) [4.3 mo and 1.6 mo], and real-world overall survival (rwOS) [19.8 mo and 4.9 mo]. For HR+ pts who received SG prior to T-DXd, response and survival data is as follows for SG and T-DXd respectively: ORR [78.3% and 42.9%], TTNT [8.6 mo and 2.8 mo], and rwOS [22.3 mo and 7.3 mo]. Among pts with HR-/HER2-low MBC, median time from MBC diagnosis to treatment with ADC #1 was 8.2 months with 2 median lines of prior therapy in the metastatic setting (2 chemotherapy); 66.7% (n=10) received prior immunotherapy. Most HR- pts received SG prior to T-DXD (n=14, 93.3%) and 40.0% (n=6) received an intervening therapy between ADCs. For HR- pts who received SG prior to T-DXd, response and survival data is as follows for SG and T-DXd respectively: ORR [64.3% and 38.5%], TTNT [6.2 mo and 2.7 mo, and rwOS [15.7 mo and 6.5 mo]. In terms of key safety parameters during treatment with T-DXd, 13.3% of pts (8/60) required a dose reduction. 16.7% (10/60) were diagnosed with interstitial lung disease (ILD)/pneumonitis of any grade including 3 pts with grade 3-4 ILD (5.0%) and 3 pts with grade 5 ILD (5.0%). During treatment with SG, 40.0% of pts (24/60) required a dose reduction. 83.3% (50/60) received growth factor support (24 pts primary prophylaxis; 26 pts secondary prophylaxis); 9 pts (15%) required treatment delay due to neutropenia. Conclusion. This study represents the largest multicenter series to date of pts treated with sequential ADCs for HR+/HER2-low or HR-/HER2-low. ORR was higher and TTNT was longer for ADC #1 than ADC #2 in all subgroups, regardless of HR+ status and ADC sequence order. An additional ~30 pts will be reported at time of final analysis. Future prospective studies are planned to further clarify the efficacy and safety of sequential ADC use and to identify biomarkers of response and resistance. Key demographic, clinical and treatment characteristics in pts with HR+ and HR- HER2-low MBC treated sequentially with T-DXd and SG (in either order, with or without intervening therapies) Abbreviations: T-DXd (trastuzumab deruxtecan), SG (sacituzumab govitecan), MBC (metastatic breast cancer), ADC (antibody drug conjugate), HR (hormone receptor), HER2 (human epidermal growth factor receptor 2), CNS (central nervous system), ET (endocrine therapy), ORR (overall response rate), TTNT (time to next treatment), rwOS (real world overall survival), CI (confidence interval) * Several pts on ADC #2 with ongoing treatment and first scan pending, hence smaller denominator for response assessment Citation Format: Laura Huppert, Reshma Mahtani, Samantha Fisch, Naomi Dempsey, Sarah Premji, Angelina Raimonde-Taylor, Saya Jacob, Laura Quintal, Jo Chien, Michelle Melisko, Ana Sandoval-Leon, Lauren Carcas, Manmeet Ahluwalia, Natasha Harpalani, Jenna Hoppenworth, Dame Idossa, Ruta Rao, Karthik Giridhar, Hope Rugo. Multicenter retrospective cohort study of the sequential use of the antibody-drug conjugates (ADCs) trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) in patients with HER2-low metastatic breast cancer (MBC) [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 PS08-04.

Abstract PS06-02: Circulating tumor DNA (ctDNA) monitoring of estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) high risk breast cancer during adjuvant endocrine therapy

Abstract Background: ctDNA monitoring during adjuvant endocrine therapy provides an opportunity to detect molecular relapse before clinically apparent recurrence. The rate and dynamics of ctDNA positivity and the frequency of asymptomatic but imaging detectable metastatic disease at the time of ctDNA detection remain unknown in high-risk ER+/HER2- breast cancers. We present results of ctDNA positivity rates in 508 and imaging results in ctDNA+ patients from a prospective, multicenter, randomized ctDNA surveillance and intervention trial, DARE (NCT04567420). Patients and methods: Patients receiving adjuvant endocrine therapy for &amp;gt; 6 months but &amp;lt; 7 years, with either (i) risk of recurrence &amp;gt; 15% calculated by PREDICT, RSPC, or CTS5, or (ii) &amp;gt; 4 positive axillary lymph nodes, or (iii) primary tumor &amp;gt; 5 cm, or (iv) 1-3 positive nodes with grade 3 histology, or &amp;gt; 3 cm tumor, or Oncotype Dx RS &amp;gt; 26, MammaPrint high risk, EndoPredict &amp;gt; 4, Prosigna score &amp;gt; 60 were eligible for ctDNA surveillance with the SignateraTM assay (Natera Inc.) every 4-6 months during routine follow up visits. ctDNA+ patients underwent systemic staging with imaging and randomized to continuation of adjuvant therapy versus switching to fulvestrant plus palbociclib if there was no evidence of distant metastatic disease. The primary objectives are to assess the incidence of ctDNA positivity in the surveillance phase and to assess if palbociclib plus fulvestrant improves relapse-free survival in 100 randomized patients. This is an updated, protocol-driven interim report to determine if screening eligibility criteria needs to be revised to keep randomization rate &amp;gt; 15% of the screened population. Results: The trial is open at 15 sites and enrolled 508 patients between May 2021 and June 2023; 882 plasma ctDNA tests were performed successfully in 364 patients (72%). The most common reason for failure to generate a personalized ctDNA assay was insufficient tissue submitted, 78% of failed tests were due to preanalytical failure, the technical failure rate was 22%. Thirty patients, 8.2% of those with results available, had &amp;gt;1 positive ctDNA result, the overall positivity rate across all assays was 3.4% (n=30/882). Patient characteristics are shown in the table (not all patients have complete data), 47% of ctDNA+ cases had &amp;gt;4 + lymph nodes. ctDNA positivity rate in the first test was 3.8%, and anytime ctDNA detection rate among those with serial testing was 7.2%. Among ctDNA+ patients, the first ctDNA draw was positive in 23 of 30 cases (77%) with 36.5 months median time (range 6-102 months) from surgery to testing. Using 12 months interval brackets from surgery to 1st ctDNA positivity, annual detection rates were 2,3% (1/44), 8.5% (7/82), 10.8% (9/83), 7.5% (4/53), 13,2% (5/38), and 6.2% (4/64), at 1st, 2nd, 3rd, 4th and &amp;gt; 5th year post-surgery, respectively, due to small sample sizes, 95% confidence broadly overlap. Five ctDNA+ patients (16.7%) had asymptomatic, imaging-detectable metastatic disease, 22 ctDNA+ patients were randomized, the goal is to accrue a total of 100 patients. Conclusions: ctDNA surveillance of ER+/HER2- breast cancers during adjuvant endocrine therapy indicate 8.3% detection rate at patient level and 3.4% at assay level. Serial screening increases detection rates as 23% of positive ctDNA tests occurred after an initial negative result. 83% of ctDNA+ patients had true molecular relapse without imaging detectable metastatic disease. Eligibility for screening on the trial is now restricted to patients with &amp;gt;4 + lymph nodes, randomization is open for any patients who are ctDNA+ including routine commercial screening. Table of patient characteristics with ctDNA result (n=364) ctDNA+ (n=30) Age &amp;lt; 50 29% 23% Age &amp;gt;50 71% 77% PR + 78% 73% PR - 7% 17% HER2 IHC negative 79% 77% Grade 1 8% 7% Grade 2 53% 50% Grade 3 29% 37% T 1 19% 17% T2 43% 43% T3 27% 27% T4 2% 7% 0 +nodes 12% 12% 1 +node 24% 10% 2 +nodes 15% 13% 3 +nodes 8% 13% &amp;gt;4 +nodes 0 47% Citation Format: Lajos Pusztai, Ekaterina Kalashnikova, Evthokia Hobbs, Ursa Brown-Glaberman, Monica Mita, Paula Klein, Fengting Yan, Sima Ehsani, Wajeeha Razaq, Alison Stopeck, Manali Bhave, Michelle Loch, Sagar Sardesai, Evanthia Roussos Torres, Mark Burkard, Femi Okubanjo, Eric Gauthier, Angel Rodriguez, Minetta Liu, Peter Kabos. Circulating tumor DNA (ctDNA) monitoring of estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) high risk breast cancer during adjuvant endocrine therapy [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 PS06-02.

Abstract PO5-01-08: The impact of Human Epidermal growth factor Receptor 2 (HER2) expression by RT-PCR on tumor characteristics and outcome in estrogen receptor (ER) positive, HER2 negative early-stage breast cancer

Abstract Background: The role of HER2 expression in HER2 negative breast cancer is evolving. Whether HER2 expression has an impact on ER positive, HER2 negative early-stage breast cancer in unclear. Oncotype DX assay Recurrence Score comprises of standardized quantitative HER2 mRNA expression levels by RT-PCR. The objective of this study was to investigate the impact of Oncotype HER2 score on tumor characteristics and outcome. Methods: All women assigned to the Clalit Health Services registry between 2006 to 2011 with ER positive, HER2 negative early-stage breast cancer whose tumor were sent for oncotype were identified. Patients in which HER2 score was reported in the oncotype results were included. Differences in age, tumor characteristics and chemotherapy administration between lower HER2 score (H1), i.e. HER2 score ≤ 9.1, to higher HER2 score (H2), i.e. 9.2-10.7, were analyzed. 5-year Kaplan–Meier for distant recurrence free survival (DRFS) and overall survival (OS) were estimated and differences between H1 and H2 were evaluated. Analyses were repeated separately for node negative and for node positive (N mic and 1-3 lymph nodes) disease. Results: A total of 1535 patients were included, 948 patients with node negative disease and 587 with node positive disease. Of these, 814 and 721 patients were categorized to the H1 and H2 groups, respectively. Median follow-up was 5.4 years. The distribution of oncotype RS was different, with significantly lower proportion of patients with RS between 0-10 and higher proportion of RS above 25 in the H1 group compared to the H2 groups. This difference was identified both for patients with node negative and node positive disease (Table). The distributions of age, tumor size and histological subtype were comparable between the H1 and the H2 groups, both for node negative and node positive disease. Within each RS group, administration of chemotherapy was comparable between H1 and H2 groups, regardless of nodal involvement. DRFS and OS were not associated with HER2 score. For RS 0-25, node negative disease, 5-year DRFS was 96.2% in H1 and 96.4% in H2 groups (p=0.92) and 5-year OS was 97.2% in H1 and 98.1% in H2 groups (p=0.39). For RS &amp;gt;25, node negative disease, 5-years DRFS was 89% in H1 and 90.8% in H2 groups (p=0.33) and 5-year OS was 90.6% in H1 and 90.8% in H2 groups (p=0.7). Similarly, for node positive disease, DRFS and OS were comparable between H1 and H2 group in all subgroups. Conclusions: Low HER2 mRNA expression by Oncotype RT-PCR assay was associated with significantly high Oncotype RS. Patients' outcome was not directly affected by HER2 score and was determined by RS. Further study is desired to clarify the role of HER2 expression in early stage, luminal breast cancer. Table. Comparison of age and tumor characteristics between low (H1) and high (H2) HER2 score Citation Format: Hadar Goldvaser, Raz Mutai, Salomon Stemmer, Iryna Kuchuk, Margarita Tokar, Shani Paluch-Shimon, Rinat Yerushalmi, Karen Drumea, Ella Evron, Amir Sonnenblick, Einav Gal-Yam, Gil Bar Sela, Ayelet Shai, Rotem Merose, Avital Bareket-Samish, Lior Soussan-Gutman. The impact of Human Epidermal growth factor Receptor 2 (HER2) expression by RT-PCR on tumor characteristics and outcome in estrogen receptor (ER) positive, HER2 negative early-stage 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 PO5-01-08.

Abstract PO5-20-02: Secondary BRain metastases prevention after Isolated intracranial progression on trastuzumab/pertuzumab or T-DM1 in pts with aDvanced human epidermal Growth factor receptor 2+ brEast cancer with addition of Tucatinib (BRIDGET)

Abstract Background: Despite treatment with trastuzumab-based therapy, up to half of patients with HER2+ advanced/metastatic breast cancer (MBC) will develop brain metastases (BrM). First-line therapy for advanced HER2+ MBC remains a taxane, trastuzumab, pertuzumab (TP) which demonstrates poor brain permeability. Isolated brain relapse with stable or absent extracranial disease remains a clinical problem in both the adjuvant (Untch et al., ESMO 2019 Congress) and metastatic settings (Noteware et al., Breast Cancer Res Treat. 2023). Current guidelines recommend continuing current systemic therapy in the setting of first isolated brain relapse following local therapy. Tucatinib, a brain-penetrable HER2-targeting tyrosine kinase inhibitor, when added to trastuzumab and capecitabine improves intracranial progression free survival (PFS) and overall survival (OS) in patients with stable or active HER2+ BrMs. We hypothesize that adding tucatinib to TP or T-DM1 in patients with HER2+ MBC with isolated brain relapse or progression could delay or prevent the development of further intracranial lesions and improve OS. Methods: BRIDGET (NCT05323955) is a single arm, phase II, multicenter study of tucatinib added to TP or T-DM1 after local therapy in patients with isolated brain relapse or progression. A total of 48 patients at 9 U.S. sites as part of the Hoosier Cancer Research Network (HCRN) with metastatic HER2+ breast cancer will be enrolled after 1st or 2nd BrM relapse or progression within 8 weeks of local therapy. Patients must currently be receiving standard of care treatment with TP or T-DM1 in the metastatic setting, or adjuvant trastuzumab-based or T-DM1 therapy with isolated brain recurrence. Extracranial disease must be stable per RECISTv1.1 or absent. Patients may not have leptomeningeal disease or untreated brain lesions over 5 mm. Patients will receive continuous tucatinib added to their current therapy (TP or T-DM1). The primary objective is intracranial PFS compared to a historical control (H0: PFS &amp;lt; 5 months (mos), HA: PFS &amp;gt; 8 mos) of the HER2CLIMB clinical trial where patients could continue on trial with isolated brain progression. In these patients, median time from brain progression to second progression or death was 7.6 mos (95% CI, 3.9 to 11.3 mos) in the tucatinib arm versus 3.1 mos (95% CI, 1.2 to 4.1 mos) in the control arm (Lin et al., J Clin Onc 2020). Secondary endpoints include PFS by RECISTv1.1, PFS of extracranial disease, locally treated versus new distant intracranial metastasis PFS, site of first progression (brain versus non-brain), OS, and toxicity in patients with BrM. Collection of correlative specimens including archival tissue, cerebrospinal fluid (optional), whole blood for ctDNA are planned. Patient-reported outcomes surveyed utilizing the FACT-BR and FACIT-Fatigue questionnaires are also included for future analyses. As of 7/06/23, accrual is 5 patients of the anticipated 48 patients overall, across 5 sites (Duke University, Dana Farber Cancer Institute, Ohio State University, Providence Portland Medical Center, and Washington University in St. Louis) currently open. An additional 4 sites are pending opening. Those interested in this trial can reach out to the study Principal Investigators, Carey Anders, MD (carey.anders@duke.edu) or Sarah Sammons, MD (sarahl_sammons@dfci.harvard.edu). Citation Format: Sarah Sammons, Amanda Van Swearingen, Laura Noteware, Nusayba Bagegni, Kelly Moulton, Stevie Threatt, Denise Jaggers, Shannon Shea, Eric Lipp, Erin Riley, Sin-Ho Jung, Gloria Broadwater, Masey Ross, Kimberly Strickland, Sasha Beyer, Alison Conlin, Aki Morikawa, Rashmi Murthy, Carey Anders. Secondary BRain metastases prevention after Isolated intracranial progression on trastuzumab/pertuzumab or T-DM1 in pts with aDvanced human epidermal Growth factor receptor 2+ brEast cancer with addition of Tucatinib (BRIDGET) [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 PO5-20-02.

Abstract GS01-01: Biomarker Results in High-risk Estrogen Receptor Positive, Human Epidermal Growth Factor Receptor 2 Negative Primary Breast Cancer Following Neoadjuvant Chemotherapy ± Nivolumab: an Exploratory Analysis of CheckMate 7FL

Abstract Background: CheckMate 7FL (CM 7FL; NCT04109066) is a prospective, phase 3, randomized, multicenter, double-blind trial investigating nivolumab (NIVO) in combination with neoadjuvant chemotherapy (NACT) and adjuvant endocrine therapy (ET) in patients (pts) with high-risk, estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2−) primary breast cancer (BC). The primary endpoint (pathological complete response, pCR) was met, resulting in a statistically significant improvement with added NIVO to NACT; residual cancer burden (RCB) 0–1 rate was meaningfully improved. NIVO benefit was larger in pts with PD-L1+ tumors (SP142 assay, % immune cells ≥ 1%). This analysis focuses on additional biomarkers to explore associations with NIVO treatment effect. Methods: The study enrolled newly diagnosed pts, stages T1c–2 N1–2 or T3–4 N0–2, grade 2 (ER 1–‍10%) or 3 (ER ≥ 1%). Pts were randomized 1:1 to NACT + NIVO 360 mg Q3W/NIVO 240 mg Q2W (arm A) or NACT + placebo (PBO; arm B). Clinical efficacy data included pCR (ypT0/is ypN0) and RCB 0–1 rates in the modified ITT (mITT) population and the SP142 PD-L1+ subgroup. Baseline PD-L1 expression from core biopsies was evaluated with the Dako 28-8 assay using the combined positive score (CPS) algorithm. Various cutoffs (CPS ≥ 1, 10, and 20) were used for this exploration. Concordance between PD-L1 SP142 and 28-8 CPS was evaluated, with assays performed on different slides from the same tumor biopsy blocks. Results of efficacy by ER and/or progesterone receptor (PR) expression, as well as Ki67 index and stromal tumor-infiltrating lymphocytes, will be presented at the meeting. Results: Overall, 830 pts were screened, 521 randomized, and 517 treated, with the primary efficacy population (mITT; n = 510) including all randomized pts but excluding 11 pts from Russian sites with insufficient follow-up. A total of 510 and 349 pts (68.4% of mITT population) were evaluated by PD-L1 SP142 and 28-8 CPS assays, respectively. The prevalence of PD-L1+ by CPS was balanced in arms A and B (52% vs 50% had CPS ≥ 1; 19% vs 16% had CPS ≥ 10, and 11% vs 9% had CPS ≥ 20, respectively). NIVO effect was larger in pts with tumors with increasing PD-L1 expression, with a ∆pCR rate (unweighted rate difference between arms A and B) of 16.6% in CPS ≥ 1 (40.4% vs 23.8% in arms A/B; 95% CI, 2.8 to 29.4), 32.4% in CPS ≥ 10 (65.7% vs 33.3% in arms A/B; 95% CI, 7.3 to 52.3), and 52.3% in CPS ≥ 20 (78.9% vs 26.7% in arms A/B; 95% CI, 18.6 to 72.4). In comparison, the ∆pCR rate was 10.7% in the mITT population (24.5% vs 13.8% in arms A/B; 95% CI, 3.9 to 17.4) and 5.7% in pts with CPS &amp;lt; 1 (14.0% vs 8.2% in arms A/B; 95% CI, -4.0 to 15.5; refer to the Table for additional details). Unweighted rate differences between arms A and B for RCB 0–1 (∆RCB 0–1 rate) followed a similar trend and were observed to be 17.0% in CPS ≥ 1, 34.4% in CPS ≥ 10, and 52.3% in CPS ≥ 20. In comparison, the ∆RCB 0–1 rate was 9.4% in the mITT population and 3.3% in pts with CPS &amp;lt; 1 (refer to the Table for additional details). Further biomarker data and cutoffs will be presented at the meeting. Conclusions: Greater PD-L1 expression was associated with higher pCR and RCB 0–1 rates, suggesting that pts with PD-L1+, high-risk, ER+/HER2− primary BC can achieve substantial pCR rates with the addition of NIVO to NACT. Table. Summary pCR and RCB 0–1 rates by PD-L1 SP142 and 28-8 CPS at various cutoffs. Note: CPS data with the cutoff at 5 will be presented at the meeting. Citation Format: Sherene Loi, Giuseppe Curigliano, Roberto Salgado, Roberto Iván Romero Díaz, Suzette Delaloge, Carlos Ignacio Rojas García, Marleen Kok, Cristina Saura, Nadia Harbeck, Elizabeth Mittendorf, Denise Yardley, Lajos Pusztai, Alberto Suárez Zaizar, Andrei Ungureanu, Felipe Ades, Rajalakshmi Chandra, Raheel Nathani, Misena Pacius, Thomas Spires, Jenny Wu, Heather McArthur. Biomarker Results in High-risk Estrogen Receptor Positive, Human Epidermal Growth Factor Receptor 2 Negative Primary Breast Cancer Following Neoadjuvant Chemotherapy ± Nivolumab: an Exploratory Analysis of CheckMate 7FL [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 GS01-01.