Positive Triple Negative Breast Cancer Research Articles

Abstract PS15-08: Final Overall Survival (OS) analysis of the SAKK 21/12 trial. CR1447 in HR+/HER2- metastatic breast cancer and androgen receptor positive triple negative breast cancer

Abstract Introduction: CR1447 (4-Hydroxytestosteron) is a compound with aromatase inhibitor and anti-androgen receptor activity and is applied transdermally. We assessed its activity and safety in metastatic breast cancer (mBC). The primary endpoint (disease control rate at week 24) was reported in 2019. We now present the final overall survival (OS) analysis of the trial. Methods In cohort A (ER+/HER2-negative metastatic disease), one prior treatment line was allowed and 29 patients (ITT 21 patients) were included. In cohort B (triple negative mBC), eight patients were included. The trial was closed in 2018 due to futility (cohort A) and slow accrual (cohort B). Results At data cut-off on 11.04.2023 92% of all patients had died. Median OS for cohort A was 35.4 months (95% CI: 24.6-49.1) in the ITT population and 19.4 months (95% CI: 2.3-36.8) in the non-ITT population (patients with more than one line of endocrine therapy). In cohort B, median OS was 10.8 months (95% CI: 3.3-28.6). Treatment was well tolerated with no new safety signals and the majority of treatment-related adverse events (TRAE) were Grade 1 and 2. The most common TRAEs were dry skin (43%), rash (16%), fatigue (16%) and nausea (16%). Discussion Despite the trial being negative in terms of the primary endpoint, cohort A (ITT) had a median OS of 35.4 months. There were no new safety signals. Mutational analysis of AR/ER is ongoing to determine benefit of this treatment in specific subgroups. CR1447 might be a candidate drug to combine with other agents (CDK4/6 inhibitors or other targeted therapies). Citation Format: Marcus Vetter, Holer Lisa, Karin Rothgiesser, Wolfgang Schönfeld, Salome Riniker, Roger von Moos, Andreas Torjan, Elena Kralidis, Manuela Rabaglio, Mathias K. Fehr, Andreas Müller, Beat Thürlimann. Final Overall Survival (OS) analysis of the SAKK 21/12 trial. CR1447 in HR+/HER2- metastatic breast cancer and androgen receptor positive triple negative 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 PS15-08.

Abstract PO1-26-06: The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model

Abstract Background: Metastatic triple-negative breast cancer (TNBC) is an aggressive sub-type of breast cancer that is challenging to treat. While the addition of immunotherapy (IT) with pembrolizumab (pembro) to chemotherapy prolongs overall survival in patients with programmed death-ligand 1 positive (PD-L1+) TNBC, few patients obtain long-term benefit. Radiotherapy (RT) can stimulate cellular damage, release of tumor antigens and promote the T cell anti-tumor response including at distant sites (abscopal response) when used with IT. The purpose of this study was to investigate the combination of RT with pembro and paclitaxel (pac) in a TNBC humanized mouse model. Methods: Human Immune System BRGS (BALB/c, Rag2-/-, IL2RγC-/-, NODSIRPa ) mice were engrafted with TNBC MDA-MB-231 cells in bilateral flanks. Treatments included: vehicle, pac 10 mg/kg intra-peritoneal (IP) weekly, pembro 15 mg/kg IP weekly, and RT 8 Gy x 3 fractions every other day the first week of treatment to one-sided tumors (contralateral tumors received no RT). Mice were treated and analyzed in the following groups: vehicle, pac + pembro, RT + pac, and RT + pac + pembro. Treatments began when tumors reached 100-300 mm3 and tumors were measured twice weekly. At the end of study, sera, lymph nodes (LNs), spleen, and tumor tissue were collected for immunohistochemistry, single cell suspensions, and flow cytometry analysis for immune cell populations. Results: All treatment arms resulted in a decrease in tumor volume when compared to vehicle with the greatest reduction in the RT + pac and RT + pac + pembro arms. Combination therapy with RT + paclitaxel (p=0.0002) and RT + pac + pembro (p=0.008) resulted in a statistically significant decrease in specific growth rate (SGR) when compared to vehicle. An abscopal effect was not observed in the non-RT tumors compared to RT-tumors in either group. RT + pembro was associated with an increase in hCD45 T cells in LNs and spleens but not in tumors. In mice that received RT, a decrease was noted in HLA-ABC class I and Intermediate Class II major histocompatibility complex (MHC). In addition, RT-tumors had reduced expression of PD-L1 and polio virus receptor (PVR) and increased expression of PD-1. The percentage of interferon gamma (IFNg+), tumor necrosis factor alpha (TNFa+) CD8+ T cells increased with radiation. This percentage was the highest in the triplet therapy with RT+ pembro + pac. Conclusion: Combination treatment with RT + immunochemotherapy resulted in a significant increase in anti-tumor activity when compared to immunochemotherapy alone, however, an abscopal effect was not observed in contralateral non-RT tumors. RT resulted in down-regulation of immune inhibitory receptors and tumor MHC. Citation Format: Anna Schreiber, Stacey Bagby, Stephen Smoots, Adrian Dominguez, Christine Fisher, Julie Lang, Todd Pitts, Jennifer Diamond. The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model [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 PO1-26-06.

Abstract PS16-01: Comparison of an Atezolizumab monotherapy window followed by Atezolizumab and chemotherapy vs. Atezolizumab and chemotherapy alone in triple negative breast cancer (TNBC) – final analysis of the neoadjuvant neoMono trial

Abstract Background: Improvement of systemic therapy of TNBC still is a medical need. Exploratory data from the neoadjuvant GeparNuevo trial suggested a benefit from an immune checkpoint inhibitor (ICI) monotherapy window in TNBC. The neoMono trial prospectively analyzed whether the addition of a preceding Atezolizumab monotherapy window prior to Atezolizumab and chemotherapy (CTX) improves pCR rates among patients (pts) with early TNBC. In an interim analysis after 100 pCR events, patients with unselected TNBC did not show a significant benefit from an Atezolizumab monotherapy window, while an exploratory analysis suggested a highly clinically relevant benefit among pts with PD-L1 positive TNBC. Here we present the final primary endpoint analysis. Methods: NeoMono is a phase 2 randomized multicenter trial that was planned to recruit a maximum of 458 female and male pts with primary TNBC (defined as ER/PR < 10% and HER2 negative) with tumor stages cT1c – cT4d (cN0 and cN+). As the protocol mandated termination of trial recruitment based on the results of the interim analysis, the final ITT population was limited to 359 pts. PD-L1 status had to be identifiable by central pathology by means of the VENTANA PD-L1 (SP142) assay and was defined by PD-L1 expression on immune cells (IC). Neoadjuvant treatment in both study arms consisted of Atezolizumab 1200 mg every 3 weeks in addition to neoadjuvant CTX (12 x Carboplatin/Paclitaxel q1w followed by 4x Epirubicin/Cyclophosphamide q3w). Combination therapy in arm A was preceded by an Atezolizumab monotherapy window of 840 mg once two weeks prior to initiation of combination therapy, while patients in arm B received no immune monotherapy window. Study goals are to compare the efficacy of neoadjuvant CTX + Atezolizumab with versus without a two-week atezolizumab monotherapy window preceding CTX + ICI (primary endpoint: pCR) and to identify biomarkers for response and resistance through analysis of sequential tissue and liquid biopsies. The neoMono statistical design uses Bayesian posterior probabilities (uniform prior distribution) and logistic regression to analyze the primary endpoint. Results: 180 pts in arm A and 179 in arm B from 34 study sites were included in the final primary endpoint analysis. Demographics and baseline characteristics as well as drug exposure were well-balanced in both arms. Posterior mean pCR rates in the ITT population in study arms A and B were 65.7% (95% high posterior density interval (HPDI): 58.5%, 72.5%) and 69% (62.2%, 75.9%), respectively. In an exploratory analysis stratified by PD-L1 IC status (negative: < 1% versus positive: ≥ 1%), pCR rates in arm A were 91.5% in the PD-L1 IC-positive group and 56.1% in the PD-L1 IC-negative group, the corresponding pCR rates in arm B were 82.2% and 64.5%, respectively. In a multivariate analysis of the ITT population including tumor size, nodal status, tumor grade, age and PD-L1 status, the odds ratio for achieving a pCR was 4.77 (p < 0.001) for PD-L1-positive and 2.36 (p=0.023) for grade 3 tumors. In an exploratory analysis including HER2 status, odds for achieving a pCR were significantly higher for patients with HER2-negative (IHC 0) vs. HER2-low tumors (OR 1.73, p=0.036). No new safety signals were observed. Conclusion: The final primary endpoint analysis of the neoMono trial demonstrated the highest pCR rates ever reported in a phase II/III trial in TNBC. While a significant impact of an ICI monotherapy window on the pCR rate after combination of CTX + ICI in an unselected ITT population could not be demonstrated, neoMono indicates for the first time in a randomized prospective setting that patients with immune active TNBC might derive particular benefit from a preceding ICI monotherapy window. The results of the neoMono trial are mainly justifying the conduction of a confirmative trial in immune active TNBC. However, our results underscore the potential role of pre-therapeutic ICI monotherapy window as part of future therapeutic concepts in TNBC. Citation Format: Hans-Christian Kolberg, Johannes Schumacher, Ramona Erber, Michael Braun, Peter A. Fasching, Eva-Maria Grischke, Christian Schem, Michael P. Lux, Mustafa Deryal, Oliver Hoffmann, Bernhard Heinrich, Georg Kunz, Kristina Lübbe, Petra Krabisch, Arndt Hartmann, Philip Raeth, Sabine Kasimir-Bauer, Cornelia Kolberg-Liedtke. Comparison of an Atezolizumab monotherapy window followed by Atezolizumab and chemotherapy vs. Atezolizumab and chemotherapy alone in triple negative breast cancer (TNBC) – final analysis of the neoadjuvant neoMono trial [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 PS16-01.

Abstract PO1-06-12: Phase II study of sitravatinib plus tislelizumab with or without nab-paclitaxel in patients with locally recurrent or metastatic triple negative breast cancer

Abstract Background: The combination of a PD-(L)1 inhibitor plus chemotherapy demonstrated promising anti-tumor activity as first-line therapy for patients (pts) with locally recurrent inoperable or metastatic PD-L1 positive triple-negative breast cancer (TNBC). However, for pts without PD-L1 expression and for those who have failed prior lines of treatment, therapeutic options are still limited. This multi-cohort, phase II trial aimed to evaluate the safety and antitumor activity of 70 mg (cohort A) or 100 mg (cohort B) sitravatinib plus tislelizumab in pts with locally recurrent or metastatic TNBC, and their combination (70 mg sitravatinib plus tislelizumab) with nab-paclitaxel in untreated locally recurrent inoperable or metastatic TNBC pts (cohort C). The efficacy of sitravatinib plus tislelizumab in cohort A and B has been reported with objective response rate (ORR) of 38.1% and 45.0%, respectively. Herein, the preliminary results of cohort C and updated results of cohort A and B were reported. Methods: Pts with untreated locally inoperable or metastatic TNBC were included in cohort C and received 70 mg sitravatinib orally once daily plus 200 mg tislelizumab intravenously on day 1 and 100mg/m2 nab-paclitaxel on days 1 and 8 every three weeks until disease progression or intolerable toxicity. The primary endpoint was ORR. Secondary endpoints included disease control rate (DCR), progression-free survival (PFS), duration of response (DOR), 1-year overall survival (OS) rate and safety/tolerability. Based on Simon’s two-stage design, > 9 responders were need in stage 1 (n=18) for the study to continue, and >19 responders were needed by the end of study (n=35) to demonstrate statistical superiority with sitravatinib plus tislelizumab and nab-paclitaxel (assumed to be around 65%) to a historical control of 46% (1-sided alpha of 0.1, power of 80%). Updated analyses were provided for cohort A (Simon’s 2 stage design) and B (Bayesian optimal phase II design). Results: Among the 18 pts in stage 1 of cohort C, 12 of them achieved confirmed response, and therefore the study proceeded to the enrollment in stage 2. As of April 30, 2023, a total of 32 pts were enrolled, with a median age of 51 years. Among the 23 efficacy evaluable pts, unconfirmed ORR was 87.0% (95% CI 66.4-97.2) (including 3 CRs and 17 PRs), with 7 pts not reaching next tumor assessment after reaching CR/PR, and confirmed ORR was 52.2% (95% CI 30.6-73.2). DCR was 95.7%. Any grade of treatment-related adverse events (TRAEs) occurred in 31 (96.9%) pts, and grade ≥3 TRAEs occurred in 5 (15.6%) pts. One (3.1%) patient experienced grade ≥3 immune-related adverse events. SAEs were reported in 3 (9.4%) pts. At the data cut-off date, the median follow-up duration for cohort A and B was 20.4 (range 1.3–24.3) months and 13.3 (range 5.1-19.1) months, respectively. The median PFS in cohort A was 8.2 (95% CI 2.8-12.4) months, and in cohort B was 5.4 (95% CI 4.2-10.9) months. Median OS was not reached in both cohorts. RNA-seq analysis showed that the suppression of immune regulatory pathways and the activation of metabolic pathways promoted early progression. Besides, baseline angiogenesis associated pathway held the potential to predict the favorable response to tislelizumab plus sitravatinib. Conclusion: In the first-line treatment of locally recurrent or metastatic TNBC, preliminary analysis of cohort C showed that sitravatinib combined with tislelizumab and nab-paclitaxel had promising anti-tumor activity with a high ORR, and the combination was generally well tolerated. In TNBC pts with less than three lines of therapy, the chemotherapy-free regimen with sitravatinib plus tislelizumab demonstrated promising PFS after a longer follow-up duration. Citation Format: Lei Fan, Xiyu Liu, Ying Xu, Xinyi Sui, Wenjuan Zhang, Linxiaoxi Ma, Xi Jin, Song-Yang Wu, Han Wang, Yi Xiao, Li Chen, Jiong Wu, Ke-da Yu, Guangyu Liu, Xin Hu, Zhonghua Wang, Yi-Zhou Jiang, Zhi-Ming Shao. Phase II study of sitravatinib plus tislelizumab with or without nab-paclitaxel in patients with locally recurrent or metastatic triple negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-06-12.

Exploring Raloxifene-based Metallodrugs: A Versatile Vector Combined with Pt(II), Palladium(II) and Nickel(II) Dichlorides and Carborates against Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) poses challenges in therapy due to the absence of target expression such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Frequently, the treatment of TNBC involves the combination of several therapeutics. However, an enhanced therapeutic effect can be also achieved within a single molecule. The efficacy of raloxifene can be improved by designing a raloxifene-based hybrid drug bearing a 2,2'-bipyridine moiety (2). Integration of platinum(II), palladium(II), and nickel(II) complexes into this structure dramatically changed the cytotoxicity. The platinum(II) dichloride complex 3 did not demonstrate any activity, while palladium(II) and nickel(II) dichloride complexes 4 and 5 exhibited various cytotoxic behavior towards different types of hormone-receptor positive (HR+) cancer and TNBC cell lines. The replacement of the two chlorido ligands in 3‒5 with a dicarbollide (carborate) ion [C2B9H11]2- resulted in reduced activity of compounds 6, 7, and 8. However, the palladacarborane complex 7 demonstrated higher selectivity towards TNBC. Furthermore, the mechanism of action was shifted from cytotoxic to explicitly cytostatic with detectable proliferation arrest and accelerated aging, characterized by senescence-associated phenotype of TNBC cells. This study provides valuable insights into the development of hybrid therapeutics against TNBC.

Abstract LB178: HP518, an oral AR-targeting PROTAC for the treatment of AR positive triple negative breast cancer with a novel mechanism of action

Abstract Triple negative breast cancer (TNBC) accounts for 15-20% of all breast carcinomas and has poor prognosis. Chemotherapy is the mainstay treatment for TNBC patients, yet with limited clinical benefit. Androgen receptor (AR) is expressed in approximately 50% of TNBC tumors and thus the anti-androgen therapy could be a promising solution for the treatment of AR+ TNBC. Nevertheless, AR inhibitors including enzalutamide and bicalutamide or the androgen biosynthesis inhibitor abiraterone have failed to demonstrate satisfying anti-tumor activity in clinical trials. We have discovered HP518, an AR-targeting PROTAC (proteolysis targeting chimera) that induces potent degradation of both the wild-type AR and AR mutants. HP518 is currently under the clinical development for the treatment of mCRPC. Here we report the preclinical data on HP518 for the treatment of AR+ TNBC. HP518 robustly degrades AR in multiple TNBC cell lines with a half-maximal degradation concentration (DC50) < 1 nM. HP518 strongly inhibits AR+ TNBC cell growth, whereas the AR inhibitor enzalutamide does not show significant anti-proliferative effect on these cells in the presence or absence of androgen. Consistent with the in vitro results, HP518 significantly and dose-dependently inhibits tumor growth in MDA-MB-453 cell line derived tumor xenograft (CDX) and patient-derived xenograft (PDX) mouse models. PI3KCA activating mutations are frequently expressed in AR+ TNBC. HP518 in combination with alpelisib, a PI3Kα inhibitor shows a synergistic anti-tumor activity. Mechanistically, HP518, but not AR inhibitor enzalutamide downregulates the mRNA expression levels of a set of DNA replication-related genes in AR+ TNBC cells, indicating a novel and ligand-independent role for AR in regulating growth of AR+ TNBC cells. Therefore, HP518, an AR-targeting PROTAC degrader holds great potential to fulfill the unmet clinical needs for the AR+ TNBC therapy. Selected pre-clinical data will be presented. HP518 structure will not be disclosed. Citation Format: Jing Li, Hongwei Yuan, Kefan Chen, Yongxu Huo, Guoqing Liu, Wu Du, Xinghai Li. HP518, an oral AR-targeting PROTAC for the treatment of AR positive triple negative breast cancer with a novel mechanism of action [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB178.

Radiomics Analysis of Contrast-Enhanced Breast MRI for Optimized Modelling of Virtual Prognostic Biomarkers in Breast Cancer.

Breast cancer clinical stage and nodal status are the most clinically significant drivers of patient management, in combination with other pathological biomarkers, such as estrogen receptor (ER), progesterone receptor or human epidermal growth factor receptor 2 (HER2) receptor status and tumor grade. Accurate prediction of such parameters can help avoid unnecessary intervention, including unnecessary surgery. The objective was to investigate the role of magnetic resonance imaging (MRI) radiomics for yielding virtual prognostic biomarkers (ER, HER2 expression, tumor grade, molecular subtype, and T-stage). Patients with primary invasive breast cancer who underwent dynamic contrast-enhanced (DCE) breast MRI between July 2013 and July 2016 in a single center were retrospectively reviewed. Age, N-stage, grade, ER and HER2 status, and Ki-67 (%) were recorded. DCE images were segmented and Haralick texture features were extracted. The Bootstrap Lasso feature selection method was used to select a small subset of optimal texture features. Classification of the performance of the final model was assessed with the area under the receiver operating characteristic curve (AUC). Median age of patients (n = 209) was 49 (21-79) years. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the model for differentiating N0 vs N1-N3 was: 71%, 79%, 76%, 74%, 75% [AUC = 0.78 (95% confidence interval (CI) 0.72-0.85)], N0-N1 vs N2-N3 was 81%, 59%, 24%, 95%, 62% [AUC = 0.74 (95% CI 0.63-0.85)], distinguishing HER2(+) from HER2(-) was 79%, 48%, 34%, 87%, 56% [AUC = 0.64 (95% CI 0.54-0.73)], high nuclear grade (grade 2-3) vs low grade (grades 1) was 56%, 88%, 96%, 29%, 61% [AUC = 0.71 (95% CI 0.63-0.80)]; and for ER (+) vs ER(-) status the [AUC=0.67 (95% CI 0.59-0.76)]. Radiomics performance in distinguishing triple-negative vs other molecular subtypes was [0.60 (95% CI 0.49-0.71)], and Luminal A [0.66 (95% CI 0.56-0.76)]. Quantitative radiomics using MRI contrast texture shows promise in identifying aggressive high grade, node positive triple negative breast cancer, and correlated well with higher nuclear grades, higher T-stages, and N-positive stages.

Abstract 6029: 225Ac/89Zr labeled anti nectin 4 radioimmunoconjugates as theranostics against nectin 4 positive triple negative breast cancer

Abstract Nectin4 (N4) is a biomarker that is overexpressed in ~62% of triple negative breast cancer (TNBC) and its lack of expression in normal tissues makes it an ideal target for the therapy and PET imaging of TNBC. Methods: We developed a fully human antibody against nectin 4 (anti N4) using phage display. Anti N4 was radiolabeled with 89Zr & 225Ac, respectively, for imaging & radiotherapy using TNBC xenograft & syngeneic mouse models. TNBC murine 4T1 cells were transduced with human N4 and N4 expression was confirmed by FACS. Biodistribution & PET imaging of 89Zr anti N4 radioimmunoconjugate (RIC) was studied in mice bearing N4 positive xenografts. Dosimetry of 225Ac anti N4 was studied in healthy mice & the therapeutic efficacy was evaluated for 90 days in mice bearing MDA MB 468 xenograft & transduced 4T1 syngeneic models. Mice were treated with 2 doses of 350 nCi administered at 10 days apart. Tumor growth was monitored by a digital caliper. Results: The pharmacokinetic profile of 89Zr-anti-N4 RIC showed biphasic distribution with a moderate elimination of 63 h. PET imaging & biodistribution of 89Zr anti N4 in mice bearing MDA MB 468 xenograft showed high tumor uptake of 13.2 ± 1.12 %IA/g at 120 h. 225Ac anti N4 was effectively internalized in MDA MB 468 and was cytotoxic to the cells with IC50 of 1.2 kBq/mL. Treatment with 225Ac anti N4 led to complete tumor remission in all mice bearing MDA MB 468 xenografts and 4T1 syngeneic model by day 20 and 28, respectively. Conclusions: 89Zr anti N4 was an effective PET imaging probe with specific uptake in tumor. 225Ac anti N4 was effective as a therapeutic agent resulting in complete remission of tumors in both mouse xenograft & syngeneic models. These results are promising for the development of anti-N4 RICs as theranostics for TNBC. Citation Format: Hanan Babeker, Fabrice Njotu, Jessica Ketchmen, Florence Tikum, Alireza Doroudi, Emmanuel Nwangele, Maruti Uppalapati, Humphrey Fonge. 225Ac/89Zr labeled anti nectin 4 radioimmunoconjugates as theranostics against nectin 4 positive triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6029.

Abstract 4925: Spatial heterogeneity of tumor boundary in mammograms is prognostic of recurrence in triple negative breast cancer (TNBC)

Abstract Introduction: Despite standard-of-care therapies, at least 25% of all TNBC patients will develop recurrence or metastasis within 3-5 years and die due to breast cancer. Early prediction of recurrence in TNBC patients from clinical mammograms would allow more aggressive intervention for higher risk patients. The tumor boundary represents the heterogeneous invasive front where malignant cells interface extracellular matrix (ECM) and contribute to invasion. In this study, we investigated role of the irregular infiltration of the normal tissue by tumor in heterogeneity of radiomics features at the boundary of the tumor. Method: Surgically treated patients with pathologically confirmed diagnosis of TNBC of any tumor size were included. All cases had node negative status and were treated with adjuvant chemotherapy. Patients with node positive or metastatic TNBCs at diagnosis, receiving neo-adjuvant chemotherapy or non-chemo regimens were excluded. Manually segmented breast lesions in mammograms from a cohort of 29 patients with 5-year outcomes were used to automatically determine the tumor boundary as a zone of 1 mm from both intra-tumoral and peritumoral regions in concordance with prior studies. Over 2000 radiomics features from the tumor boundary and the central regions of the tumor were extracted to quantify heterogeneity, obscure margins, spiculations, texture, breast fat percentage, shape, and size of the tumor. Recursive feature elimination using random forest classifier was used to reduce feature dimensionality to prevent over-fitting and predict recurrence in TNBC patients. Results: We observed that tumor boundary heterogeneity as quantified by continuous gradient magnitude features at pixel level was significantly better at predicting lethality for TNBC patients when compared to usual radiomic features (gradient, texture, and shape features) extracted from the entire tumor, as done in prior radiomics analyses. Continuous gradient magnitude features quantifying spatial heterogeneity of the tumor boundary were found to be superior to texture features in providing estimation of local changes in pixel-level heterogeneity. In a three-fold validation framework, continuous gradient features were associated with a mean AUC of 0.82 (std 0.17) and better differentiated patient lethality risk as compared to gradient, texture, and shape features of the entire tumor (mean AUC of 0.27 (std 0.11)). Conclusions: To the best of our knowledge, this is the first time that heterogeneity features of a tumor quantified by continuous gradient magnitude features from tumor boundary, as observed in routine clinical mammograms, have been shown to predict TNBC lethality. This model will be validated in a larger cohort in future studies. Citation Format: Soumya Ghose, Cynthia Davis, Sanghee Cho, Yesim Polar, Fiona Ginty, Sunil Badve. Spatial heterogeneity of tumor boundary in mammograms is prognostic of recurrence in triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4925.

Abstract 6027: 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts

Abstract Background: About 80% of colorectal cancer (CRC) and 50 % of Triple-Negative breast cancer (TNBC) patients overexpress epidermal growth factor receptor (EGFR). Mutations in the KRAS oncogene (present in 40% of mCRC) lead to constitutive over-activation of EGFR and drive de novo resistance to anti-EGFR drugs. Here, we propose to target KRAS-mutant/BRAF mutant EGFR positive mCRC and TNBC using 225Ac-labeled matuzumab, a humanized anti-EGFR monoclonal antibody. Methods: p- -SCN-macropa was used to conjugate matuzumab for radiolabeling with 225Ac and SCN-deferoxamine was used to conjugate matuzumab for labelling with 89Zr. The radioimmunoconjugates were characterized by flow cytometry, HPLC and iTLC. in vitro cytotoxicity was evaluated in EGFR-positive mCRC, TNBC cell lines and 3D spheroids with different levels of EGFR density. Tumor growth was monitored using digital caliper. Mice were treated with either 10 MBq of 89Zr-matuzumab for imaging or three doses of 13 KBq/dose administered of 225Ac-matuzumab 10 days apart. In vivo study endpoint was tumor volume greater than or equal to 1500 mm3. Results: Flow cytometry showed about 95% binding to the cells in all EGFR-positive colorectal cell lines (DLD-1, SW620, SNU-C2B, HT-29) and breast cancer cell lines (MDA-MB-468, MDA-MB-231). in vitro studies showed enhanced cytotoxicity of 225Ac-matuzumab compared with matuzumab. IC50 in the MDA-MB-468 cell line for 225Ac-matuzumab (1.86 ± nM) was 35 times more effective than matuzumab (65.25± 7 nM). Similar trends were observed in the other KRAS-mutant mCRC cell lines and breast cancer cell lines. In 3D spheroid models, the IC50 of 225Ac-matuzumab (3.0 ± 2 nM) in MDA-MB-468, was 20.79 times more effective than matuzumab (62.3 ± 1.38 nM). Similar trends were observed for all the other spheroid models as well. High uptake of 89Zr-matuzumab was observed in both mCRC and TNBC xenografts. 225Ac-matuzumab slowed tumor growth rate in MDA-MB-468 and MDA-MB-231 tumors models compared with control antibody or non-treated controls for 30 days. This study is still ongoing and will last for 2 more months. Conclusion: 225Ac-matuzumab shows very promising outcomes in KRAS-mutant mCRC models and breast cancer models and warrants further investigation. Citation Format: Florence Anjong Tikum, Humphrey Fonge, Fabrice Njotu, Hanan Babeker, Jessica K. Pougoue, Nikita Henning, Alireza Doroudi. 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6027.

Abstract 4086: ABN202 (anti-Trop-2-interferon-beta mutein): A potent antibody-cytokine fusion protein for the treatment of Trop-2 positive solid tumors

Abstract Trop-2, trophoblast cell-surface antigen 2, is a type 1 transmembrane glycoprotein overexpressed in many solid cancers, including breast, lung, pancreatic, bile duct and bladder cancer. Overexpression of Trop-2 in cancer patients is associated with disease progression and poor prognosis. The antibody-drug conjugate (ADC) targeting Trop-2, Sacituzumab-govitecan (Trodelvy®), is approved for patients with triple-negative breast cancer (TNBC) and bladder cancer. However, Trop-2 targeting ADCs exhibit a high frequency of grade 3/4 adverse events and a short duration of response. Therefore, there is an unmet medical need for new treatment strategies beyond ADCs. In a previous study, we designed ABN202 (αTrop-2) to comprise a Trop-2 targeting antibody (Sacituzumab) and IFN-β mutein (ABN102) for the Trop2-positive tumor-specific delivery of ABN102. We confirmed anti-cancer activities of ABN202 against Trop-2 positive bladder cancer. In this study, we evaluated in vitro and in vivo anti-cancer efficacy of ABN202 (αTrop-2) in Trop-2 positive TNBC, bile duct cancer and bladder cancer cell lines. To identify response biomarkers for ABN202 (αTrop-2), we analyzed cell lines exhibiting both response and non-response to ABN202 (αTrop-2). In conclusion, ABN202 (αTrop-2) demonstrated potent anti-cancer efficacy compared to Trodelvy®. Our results support ABN202 (αTrop-2) as a promising drug candidate against Trop2-positive solid tumors. Citation Format: Hee Geon Park, Hyun Kyung Lee, Myeung Ryun Seo, Daa Eun Kim, Sang Beom Bang, Ji Yang Lee, Sung Youl Hong, Kyoung Song, Chan Gyu Lee, Hae Min Jeong, Sae Hyung Lee, Na Young Kim, Jun Young Choi, Young Kee Shin. ABN202 (anti-Trop-2-interferon-beta mutein): A potent antibody-cytokine fusion protein for the treatment of Trop-2 positive solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4086.

Cost-effectiveness analysis of toripalimab for metastatic or recurrent triple-negative breast cancer.

Toliparibizumab in combination with nab-paclitaxel (T+N) has excellent efficacy inmetastatic or recurrent triple-negative breast cancer (TNBC), but the optimal choice of sequence of therapy is unclear given the trade-offs between quality of life and cost. Cost-effectiveness analyses can quantify these tradeoffs, leading to more informed decisions. Our objective was to assess the societal cost-effectiveness of the T+N regimen for metastatic or recurrent TNBC. Clinical data were extracted from a multicenter, randomized, double-blind trial, TORCHLIGHT (NCT04085276). Patients were randomized into the T+N group or placebo plus nab-paclitaxel (P+N) group. 531 patients from 53 study locations were randomly assigned (T+N, n=353; P+N, n=178) into intend to treat (ITT) population; 200 and 100 patients, respectively had programmed death protein 1 (PD-L1) positive TNBC. A Markov model was established with a 21-day cycle length. Costs were acquired from local hospitals, effect parameters included quality-adjusted life year (QALY) and incremental cost-effectiveness ratio (ICER). The cost differences were 47,538.3 CNY in ITT population (T+N, 143,725.67 CNY; P+N group, 96,187.37 CNY) and 29,258.84 CNY in PD-L1+ subgroup (T+N, 100,128.28 CNY; P+N group, 70,869.45 CNY). Meanwhile, the IEs were 0.03409 in the ITT population (T+N, 0.55323 QALY; P+N, 0.51914 QALY) and 0.03409 in the PD-L1+ subgroup (T+N, 0.42327 QALY; P+N, 0.37628 QALY). The ICERs between T+N and P+N groups were 1,394,548.41 CNY/QALY in the ITT population and 622,663.98 CNY/QALY in the PD-L1+ subgroup. We also analyzed the cost-effectiveness of toripalimab could be received in the Chinese medical insurance catalog. If toripalimab could be reimbursed at an 80% rate, the cost differences were changed to 16,598.99 CNY in ITT population (T+N, 112,786.36 CNY; P+N group, 96,187.37 CNY) and 7,704.58 CNY in PD-L1+ subgroup (T+N, 78,574.03 CNY; P+N group, 70,869.45 CNY). Meanwhile, the IEs remained unchanged. The ICERs between T+N and P+N groups were changed to 486,935.82 CNY/QALY in the ITT population and 163,962.96 CNY/QALY in the PD-L1+ subgroup. Sensitivity analyses indicated the stability of the model and the impact of utility. At current drug prices, the T+N group is not more cost-effective than the P+N group, but after incorporating toripalimab into medical insurance, the T+N group will be more cost-effective for patients with PD-L1+ metastatic or recurrent triple-negative breast cancer.

Identification of a targetable JAK-STAT enriched androgen receptor and androgen receptor splice variant positive triple-negative breast cancer subtype

Triple-negative breast cancer (TNBC) is an aggressive subtype with no targeted therapeutics. The luminal androgen receptor (LAR) subtype constitutes 15% of TNBC and is enriched for androgen receptor (AR) and AR target genes. Here, we show that a cohort of TNBC not only expresses AR at a much higher rate (∼80%) but also expresses AR splice variants (AR-SVs) (∼20%), further subclassifying LAR-TNBC. Higher AR and AR-SV expression and corresponding aggressive phenotypes are observed predominantly in specimens obtained from African American women. LAR TNBC specimens are enriched for interferon, Janus kinase (JAK)-signal activator and transducer (STAT), and androgen signaling pathways, which are exclusive to AR-expressing epithelial cancer cells. AR- and AR-SV-expressing TNBC cell proliferation and xenograft and patient-tumor explant growth are inhibited by AR N-terminal domain-binding selective AR degrader or by a JAK inhibitor. Biochemical analysis suggests that STAT1 is an AR coactivator. Collectively, our work identifies pharmacologically targetable TNBC subtypes and identifies growth-promoting interaction between AR and JAK-STAT signaling.

Clinicopathological and prognostic value of TIL and PD L1 in triple negative breast carcinomas

Triple negative breast cancer (TNBC), a highly aggressive subtype of breast cancer, accounts for 15 % of all diagnosed breast cancers. This group, which has the worst clinical outcome, high recurrence rate and poor prognosis, does not benefit from specific treatment. Therefore, there is a need to develop more effective biomarker and therapeutic strategies especially for this group. A positive level of immunity has been found to be associated with patient survival in various organ cancers. More specifically, tumor infiltrating lymphocytes (TIL) have been documented to have strong prognostic value. The programmed cell death 1 (PD 1) protein on the surface of T lymphocytes is activated by the Programmed cell death ligand 1 (PD-L1) protein on the cancer cell surface. PD- L1 is thought to form a pathway that results in suppression of antitumor responses when activated. Patients with breast cancer (BC) who underwent resection without neoadjuvant chemotherapy between 2010 and 2020 were included in this study. Of the 302 BCs examined, 21 constitute the group with TNBC. In our study, the mean age of the Triple positive breast cancer (TPBC) and TNBC groups was similar (55.67 ± 12.61 vs. 53.23 ± 8.21, p = 0.384). There was no significant correlation between TPBC and TNBC and tumor size, lymph node, histological grade, and PD-L1 positivity in the center of the tumor (all p-value >.05). It was observed that tumor stage was higher in patients with TNBC than in patients with TPBC (19 % vs. 1.1 %, p = .002). The Ki 67 proliferation index was found to be higher in patients with TNBC than in patients with TPBC (90.5 % vs. 41.8 %, p .001). Although not statistically significant, clinically, CD 3 and CD 8 immune scores with high tumor margin were higher in patients with TNBC than in patients with TPBC (90.4 % vs, 9.6 % and 85.7 % vs. 14.3 %, respectively). Positive expression of PD-L1 at the tumor margin was significantly higher in patients with TNBC than patients with TPBC (20.3 % vs, 52.4 %, p = .002). By Kaplan-Meier analysis, the survival distribution of CD 3 and CD 8 immunoscore, tumor central and margin PD-L1 values were compared. Mean follow-up was 136.18 months (range, 1 – 144 months); and the 10-year Overall Survival (OS) estimate for the population was 90.9 % (95 % CI, 85.5 – 96.7). In this study, this difference was not statistically significant according to the log-rank test. In this study, we aimed to evaluate the relationship between CD 3, CD 8 T lymphocyte immune score and PD-L1 expression at the tumor center and margin in TNBC, the prognostic value and clinicopathological significance of this relationship.

Association between pCR, TILs, and Ki-67 at baseline and after 2 weeks in patients with triple-negative breast cancer (TNBC) treated with atezolizumab and chemotherapy +/- a preceding atezolizumab monotherapy window: A translational analysis of the neoMono trial.

595 Background: neoMono randomized patients (pts) with triple negative breast cancer (TNBC) to receive (Arm A) or not to receive (Arm B) 2-week Atezolizumab monotherapy prior to neoadjuvant 24-week Atezolizumab + chemotherapy. In prespecified interim analysis, no difference regarding pathological complete response (pCR) was observed among all pts. However, in regard to pCR rates, pts with PD-L1 positive TNBC seem to benefit from addition of the monotherapy window. Here we analyze the association between central TILs and Ki-67 at baseline (BL) / after 2 weeks (2w) and pCR. Methods: Ki-67 expression (% positive tumor cells) was analyzed using immunohistochemistry. Analysis of stromal TILs was performed according to the International TILs Working Group. Differences from BL at the 2w time point were denoted as Ki-67-diff and TIL-diff, respectively. Associations between pCR and BL/2w measurements were analyzed using logistic regression. Akaike information criterion (AIC) was used to evaluate goodness-of-fit between models. Since the a priori chosen biomarker thresholds ( < = 30% [Ki-67] and < = 60% [TILs]) resulted in very low subgroup sizes, k-means clustering analysis was performed and association of the cluster labels with pCR was then investigated. Results: The analysis included 50 (Arm A) and 51 (Arm B) pts. The threshold of Ki-67 ( < = 30%) was reached in 98% (BL) and 92% (2w), that of TILs ( < = 60%) in 11% (BL) and 18% (2w), respectively. PD-L1 (BL) was < = 1 in 26%. In separate logistic regression models (including BL and change), both BL-Ki-67 and BL-TILs were significantly though moderately associated with pCR. A combined model using both biomarkers yielded the best AIC. BL-Ki-67 and BL-TILs, as well as TIL-diff were highly significantly though again moderately associated with pCR. Cluster analysis I (using BL-Ki-67, Ki-67-diff, and PD-L1) yielded cluster 1 (medium BL-Ki-67 and subsequent increase) with a pCR rate of 50% compared to 77% in cluster 2 (high BL-Ki-67 and decreasing Ki-67). Similarly, cluster analysis II (using BL-TILS, TILS-diff and PD-L1) yielded cluster 3 (low BL-TILs/non-essential TILs change) with a low pCR rate of 55% compared to 84.4% and 85.7% for clusters 4 (low BL-TILs /substantial increase) and 5 (high BL-TILs/non-essential change), respectively. In a combined regression model of all clusters above, clusters 2 and 4 had the highest pCR probability. Conclusions: Our results demonstrate that while BL-Ki-67 and BL-TILs are highly informative of pCR probability, Ki-67-diff and even more so TIL-diff added further significant information. Analysis of the full neoMono dataset will allow us to investigate this association further and to potentially develop a predictive algorithm regarding pCR based on baseline and dynamic biomarkers.

Androgen Receptor Status in Triple Negative Breast Cancer: Does It Correlate with Clinicopathological Characteristics?

Triple negative breast cancer (TNBC) is a breast carcinoma subtype that neither expresses estrogen (ER) and progesterone receptors (PR) nor the human epidermal growth factor receptor 2 (HER2). Patients with TNBC have been shown to have poorer outcomes mainly owing to the limited treatment options available. However, some studies have shown TNBC tumors expressing androgen receptors (AR), raising hopes of its prognostic role. This retrospective study investigated the expression of AR in TNBC and its relationship with known patient demographics, tumor and survival characteristics. From the records of 205 TNBC patients, 36 had available archived tissue samples eligible for AR staining. For statistical purposes, tumors were classified as either "positive" or "negative" for AR expression. The nuclear expression of AR was scored by measuring the percentage of stained tumor cells and its staining intensity. AR was expressed by 50% of the tissue samples in our TNBC cohort. The relationship between AR status with age at the time of TNBC diagnosis was statistically significant, with all AR positive TNBC patients being greater than 50 years old (vs 72.2% in AR negative TNBC). Also, the relationship between AR status and type of surgery received was statistically significant. There were no statistically significant associations between AR status with other tumor characteristics including "TNM status", tumor grade or treatments received. There was no statistically significant difference in median survival between AR negative and AR positive TNBC patients (3.5 vs 3.1 years; p = 0.581). The relationship between OS time and AR status (p = 0.581), type of surgery (p = 0.061) and treatments (p = 0.917) were not statistically significant. The androgen receptor may be an important prognostic marker in TNBC, with further research warranted. This research may benefit future studies investigating receptor-targeted therapies in TNBC.

Abstract 2390: Claudin-4 probe identifies triple negative breast cancer using multispectral optoacoustic tomography

Abstract Background: Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer. The cancer is known for the lack of estrogen and her2 receptors. TNBC has a 5-year survival rate of 77% as for the other breast cancers averaging out at 93%. The CL-750 probes are made to identify the claudin-4 that is expressed in TNBC, making it easy to identify the cancer quickly so we can treat quickly. Methods: TNBC, aggressive pancreatic and kidney cancer cell lines were used to assess the expression of claudin-4 via western blot. Based upon the C-terminal fragment of Clostridium perfingens, we synthesized a 30 aa peptide. CL peptide was conjugated to amine reactive HiLite 750 nm fluorescent dye. The CL-750 probes were purified using dialysis to remove unattached dye. MDA-MB-468 (TNBC), MDA-MB-231 (TNBC), S2VP10 (pancreatic), and 293 (kidney) cells were incubated with CL-750 probes for 30 minutes and evaluated with near infrared-fluorescence using Odyssey imaging software. Using the treated cells were then scraped into agar tissue mimicking phantoms, the probes were assessed for optoacoustic activity using the MSOT (Multispectral optoacoustic tomography). Results: Using western blot to show expression of claudin-4 within cell lines the S2VP10 pancreatic (positive control) showed the most expression of claudin-4, while the 293 kidney cells showed a lesser amount. Both MDA-MB-468 and MDA-MB-231 TNBC cells showed the lowest amount of claudin-4 nonetheless both showed enough to continue with experiments. Cell line S2VP10 showed an extreme amount of binding to probe, while as the probe also bound to both smaller amount of claudin positive breast cancer cell line (MDA-MB-231) and larger amount of claudin breast cancer cell line (MDA-MB-468). Both CL-Short-750 and CL-Long-750 showed signal using MSOT. The CL-Long-750 showed 2x as much signal as CL-Short-750 making the Cl-long-750 probe more efficient in identifying claudin positive cell TNBC (p<0.05). Conclusion: Both CL-750-probes have the capability of identifying claudin-4 positive cell lines, but CL-Long-750 was more effective and had greater binding. Citation Format: Laycee Parsons, William M. MacCuaig, Lacey R. McNally. Claudin-4 probe identifies triple negative breast cancer using multispectral optoacoustic tomography [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2390.

Variable Landscape of PD-L1 Expression in Breast Carcinoma as Detected by the DAKO 22C3 Immunohistochemistry Assay.

In 2020, pembrolizumab was approved as a therapy for triple-negative breast cancer (TNBC) with the companion diagnostic DAKO 22C3 programmed death ligand-1 (PD-L1) immunohistochemistry assay. The study aimed to determine the landscape of PD-L1 expression as detected by the DAKO 22C3 PD-L1 assay in breast cancer subtypes and compare the clinicopathologic and genomic characteristics of PD-L1 positive and negative TNBC. PD-L1 expression using the DAKO 22C3 antibody was scored using a combined positive score (CPS) and positive status was defined as CPS ≥10. Comprehensive genomic profiling was performed using the FoundationOne CDx assay. Of the 396 BC patients stained with DAKO 22C3, the majority were HR+/HER2- and TNBC (42% and 36%, respectively). Median PD-L1 expression and frequency of CPS ≥10 was highest in TNBC cases (median: 7.5, 50% CPS ≥10) and lowest in the HR+/HER2- group (median: 1.0, 15.5% CPS ≥10) (P < .0001). A comparison of PD-L1 positive and PD-L1 negative TNBC demonstrated no significant differences in clinicopathologic or genomic characteristics. TNBC tissue samples from the breast did have an observed enrichment for PD-L1 positivity compared to TNBC tissue samples from a metastatic site (57% vs. 44%), but this was not statistically significant (P = .1766). In the HR+/HER2- group, genomic alterations in TP53, CREBBP, and CCNE1 were more prevalent and genomic loss of heterozygosity was higher in the PD-L1(+) group compared to the PD-L1(-) group. The subtypes of breast cancer have distinct patterns of PD-L1 expression, supporting that further research of immunotherapies may include specific evaluation of optimum cutoffs for non-TNBC patients. In TNBC, PD-L1 positivity is not associated with other clinicopathologic or genomic features and should be integrated into future studies of immunotherapy efficacy.

Abstract P4-01-02: Results from a dose escalation phase 1b study of palbociclib and avelumab in advanced breast cancer in the PAveMenT Trial

Abstract Background CDK4/6 inhibitors may trigger anti-tumour immunity, both through tumour cell intrinsic and extrinsic mechanisms, which can be enhanced by immune checkpoint blockade in pre-clinical studies. Although most triple negative breast cancers (TNBC) are resistant to CDK4/6 inhibition, palbociclib (palbo) has activity in pre-clinical models of the luminal androgen receptor (LAR) subtype. Here we report the dose finding phase Ib cohort A of the PAveMenT trial combining avelumab and palbociclib Methods The PAveMenT phase 1b trial consists of a dose finding phase (cohort A), to be followed by an expansion in androgen receptor positive (AR+) TNBC (Cohort B). The phase 1B phase investigated palbo dosing schedules (75mg intermittent dosing (ID), 100mg continuous dosing (CD) and 125mg ID) in combination with the anti-PD-L1 antibody, avelumab 10mg/kg 2-weekly (cohort A) to determine the optimal schedule for cohort B. The CD dose-level was pre-specified as the preferred schedule if tolerated, due to the proliferative nature of TNBC and potential for tumour re-growth with ID. Patients with previously treated advanced breast cancer (ABC) of any histology with measurable disease and adequate organ function, who had not received prior immunotherapy or CDK4/6 inhibitors or more than 2 lines of chemotherapy for ABC, were eligible for cohort A. Dose-limiting toxicities (DLTs) were defined as Grade(G) 4 neutropenia, complicated G3 neutropenia or G4 thrombocytopenia, or ≥G3 immune toxicity during cycle 1. AR staining of ≥10% using the SP107 antibody (Ventana) was considered AR+. PD-L1 was evaluated using CC23 Pharma Dx antibody (DAKO) and PD-L1 positive defined as CPS score of ≥10%. Results Fourteen patients were recruited to Part A, all female, 12 with TNBC, two with ER positive/HER2 negative ABC, median age 53.5 years. Three evaluable patients received palbo 75mg/day ID without DLTs, therefore two further dose levels were opened in parallel. Three evaluable patients received palbo 125mg/day ID without DLTs. Due to a DLT of fever with G3 neutropenia in one of 3 patients receiving palbo 100mg CD, 3 further evaluable patients received 100mg CD without DLTs. Two patients were not evaluable for DLTs having not received a full cycle of treatment so were replaced. One case of grade 3 colitis and one case of grade 2 hypothyroidism (both 100mg CD) occurred outside the DLT period. Amongst 12 patients with TNBC, metastatic tissue was available for 11, archival breast tissue for one. Four of 12 patients were AR+. Five of 10 TNBC patients with sufficient tissue were PD-L1 positive, all of whom had previously tested negative with the SP142 antibody (Ventana). One of the 5 PD-L1+ and 2/5 PD-L1 negative TNBC cases were also AR+. TNBC patients received a median of 2 cycles of treatment (range 1-17). Both ER+ patients were AR+ and PD-L1 negative; one progressed after 4 cycles, the other remains on treatment at 12 cycles. The 100mg CD schedule was selected for cohort B. Conclusions All schedules were tolerable, with activity observed in patients with both ER positive and TNBC cancers. Cohort B of the study is open to recruitment for patients with AR+ TNBC. NCT04360941. Citation Format: Alicia F. Okines, Houman Moghadam, Laura Sparks, Kabir Mohammed, Kathryn Dunne, Ashutosh Nerurkar, Peter Osin, Claire Swift, Ruth Sardinha, Nicholas Turner. Results from a dose escalation phase 1b study of palbociclib and avelumab in advanced breast cancer in the PAveMenT Trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-02.

Abstract P3-02-03: A phase Ib trial of bintrafusp alfa and eribulin in patients with metastatic triple negative breast cancer (TNBC)

Abstract Background: Metastatic TNBC is an aggressive breast cancer subtype with poor prognosis and limited systemic therapy options. While pembrolizumab in combination with chemotherapy is approved for PD-L1 positive TNBC, limited immunotherapy options exist for patients with progressive and/or PD-L1 negative disease. TGFβ released by cancer cells and stromal fibroblasts attenuates the intrinsic antitumor potential of immune cells within the tumor microenvironment mediating resistance to immunotherapy. Consequently, inhibition of TGFβ signaling could potentially enhance antitumor responses to anti-PD-L1/PD-1 therapies. Bintrafusp alfa is a bifunctional fusion protein composed of the extracellular domain of TGF-β receptor II (a TGF-β “trap”) fused to a human IgG1 monoclonal antibody blocking programmed cell death ligand 1. Preclinical studies have shown that eribulin downregulates TGFβ by phosphorylation of Smad proteins. Therefore, combining eribulin with bintrafusp alfa may have a synergistic effect. This study evaluated the combination of bintrafusp alfa with eribulin in patients with metastatic TNBC. Methods: This is a phase 1b, open label, single center study evaluating bintrafusp alfa in combination with eribulin in patients with metastatic TNBC who had relapsed/progressed on prior therapies. Patients with ER/PR ≤10% with measurable disease were enrolled. Patients who received prior anti-PD-1/PD-L1 therapies in the metastatic setting were excluded. Patients received bintrafusp alfa 1200 mg intravenously every 2 weeks in combination with eribulin (1.4 mg/m2 (dose level 1), 1.1 mg/m2, or 0.7 mg/m2) on days 1, 8, 22, 29 on every 6-week cycle. Primary objectives were to determine the recommended phase II dose (RP2D) as well as to evaluate the safety and tolerability of eribulin in combination with the fixed dose of bintrafusp alfa. Secondary objective was to determine the overall response rate (ORR) according to RECIST 1.1. Bayesian optimal interval (BOIN) design was employed to identify the RP2D. Toxicities assessed using CTCAE v4.03. Tumor assessments were performed every 6 weeks. Results: A total of 25 patients were enrolled on the study. Twenty-one patients were evaluable (3 screen failures, 1 received only one dose of study treatment). Median age 59 (range 27-85). Median number of prior therapies 2 (range 0-8). The most common reason for protocol discontinuation was disease progression (n = 15, 71%). Four patients experienced dose limiting toxicities (DLTs); 3 with decreased neutrophil count and 1 with increased aspartate aminotransferase. Five patients (24%) experienced grade 4 toxicities (increased aspartate aminotransferase, hypokalemia, hypophosphatemia, neutropenia). Nine patients (43%) experienced grade 3 toxicities. Three patients (14%) discontinued study due to toxicity. Total of 2 deaths were observed, none related to treatment. Most common toxicities (any grade) include anemia (n = 13 patients), elevated aspartate aminotransferase (11), neutropenia (n = 10), elevated aminotransferase (9), headache (n = 9), hypokalemia (n = 8), hyperglycemia (n = 8), leukopenia (n = 8), and fatigue (n = 8). RP2D was eribulin 1.1 mg/m2 with bintrafusp alfa 1200 mg. Six patients had PR (28.6%), 2 had SD (9.5%) and 12 had PD (57.1%) as the best response. One patient withdrew before response evaluation. Median PFS was 1.7 months (95% CI: (1.2, 5.9) and median OS was 11.1 months (95%CI: (5.2, 15.7). Conclusions: The combination of bintrafusp alfa with eribulin has manageable safety profile with meaningful clinical activity in patients with TNBC. Further studies evaluating TGF inhibitors in breast cancer are warranted. Citation Format: Senthil Damodaran, Diane Liu, Jill Schwartz, Vicente Valero, David Ramirez, Sadia Saleem, Naoto T. Ueno, Nuhad K. Ibrahim, Meghan S. Karuturi, Rashmi K. Murthy, Stacy Moulder, Jennifer K. Litton. A phase Ib trial of bintrafusp alfa and eribulin in patients with metastatic triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-02-03.