Mesenchymal Stem-like Research Articles

Triple Negative Breast Cancer: Molecular Subtype-Specific Immune Landscapes with Therapeutic Implications.

Triple Negative Breast Cancer (TNBC) is characterized by distinct molecular subtypes with unique biological and clinical features. This systematic review aimed to identify articles examining the differences in the tumor immune microenvironment (TIME) across different TNBC molecular subtypes. Six studies meeting inclusion criteria were analyzed, utilizing gene expression profiling and bioinformatic analyses to classify TNBC samples into molecular subtypes, as well as immunohistochemistry and cell deconvolution methods to characterize the TIME. Results revealed significant heterogeneity in immune cell composition among TNBC subtypes, with the immunomodulatory (IM) subtype demonstrating robust immune infiltration, composed mainly of adaptive immune cells along with an increased density of CTLA-4+ and PD-1+ TILs, high PD-L1 tumor cell expression, and upregulation of FOXP3+ Tregs. A more immunosuppressive TIME with a predominance of innate immune cells and lower levels of tumor-infiltrating lymphocytes (TILs) was observed in luminal androgen receptor (LAR) tumors. In mesenchymal stem-like (MSL) tumors, the TIME was mainly composed of innate immune cells, with a high number of M2 tumor-associated macrophages (TAMs), while the BL and M tumors displayed poor adaptive and innate immune responses, indicating an "immune-cold" phenotype. Differential activation of signaling pathways, genomic diversity, and metabolic reprogramming were identified as contributors to TIME heterogeneity. Understanding this interplay is crucial for tailoring therapeutic strategies, especially regarding immunotherapy.

Abstract 5955: In Silico dissection of immune infiltrate signatures that are detected by DetermaIO, a predictor of response to immune therapy

Abstract Background: The composition of tumors includes not only malignant but also immune, stromal and other cell types. Understanding this dynamic tumor immune microenvironment (TIME) is important to guide treatment and develop novel therapies and markers. We have previously validated immuno-oncology gene expression signatures (DetermaIO (DTIO) and a 101-gene algorithm), that predict efficacy of checkpoint inhibitors (ICI) based on distinguishing immunomodulatory (IM), mesenchymal stem-like (MSL), and mesenchymal (M) phenotypes. In this study we used TCGA and clinical cohorts to identify immune infiltrate populations within these defined TIME spaces and their association with ICI treatment. Methods: We derived novel human immune infiltrate signatures from a translation of murine ImmGen cell populations and a search for conserved co-expression of immune markers across multiple tumors. In total, 20 tumors from TCGA were employed for derivation and analysis encompassing 7163 unique samples. These novel signatures were compared to published immune infiltrate signatures and then their association with ICI efficacy and each other assessed in three cohorts treated with ICI therapy, IMvigor210 and an additional bladder cohort, comprising 272 and 89 patients with censored outcome results, and a melanoma cohort (N=105). Results: The ImmGen analysis created 35 immune cell signatures and pan-tumor conserved co-expression of immune markers created eight signatures. The co-expression signatures often contained a mixed population of cell-type markers, though largely dominated by either myeloid or lymphoid markers. These signatures showed highly reproducible proportions of samples with strong expression between train and test TCGA sets. Most immune signatures had their highest representation in IM and DTIO+ tumors, however there was also consistent identification of presumptive immune infiltrate presence in MSL, M and DTIO negative cases. Two of the conserved co-expression signatures, one comprised of B-cell markers, and the other of T cell and other lymphoid markers, were associated with ICI efficacy in IMvigor210 and validated in the other “real-world” bladder cohort (B-cell: OR=0.8, p=0.022, T lymphoid: OR=0.7, p=0.005). Both signatures also had significant association with outcome in the cohort with clinical response outcomes, being strongest in patients after treatment had initiated. Conclusions: These cell-type signatures may be identifying novel immune infiltrate populations that co-exist within the tumor immune microenvironment and are potentially predictive of ICI response. The two signatures were not independent of DTIO in either cohort, suggesting that the 27-gene algorithm DTIO largely incorporates this information. This analysis begins to dissect the complex physiology of the tumor immune microenvironment that mediates response to immune therapy. Citation Format: Brian Z. Ring, Catherine T. Cronister, Robert S. Seitz, Douglas T. Ross, Brock Schweitzer, David R. Gandara. In Silico dissection of immune infiltrate signatures that are detected by DetermaIO, a predictor of response to immune therapy. [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 5955.

Abstract 4522: Pathologic complete response rate across triple negative breast cancer subtypes in the IMMUcan study

Abstract Background: IMMUcan (SPECTA NCT02834884) is a European public-private effort to generate molecular and cellular profiling data of the human tumor microenvironment (TME) from up to 3,000 patients, to better understand how the immune system and tumors interact. Triple-negative breast cancer (TNBC) is a heterogenous disease with distinct molecular subtypes characterized by different gene expression, genomic profiles, and clinical outcomes. Here, we explored the association between molecular subtypes and response to neoadjuvant chemotherapy as well as levels of immune cell infiltration in the prospective IMMUcan TNBC cohort. Methods: At the cut-off date on June 29th, 2022, we identified a first cohort of 132 patients to perform preliminary analyses, of which 109 had pre-treatment RNAseq data available. Among those, pathological Complete Response (pCR) information was available for a total of 86 patients. Preliminary data included the density of CD3+, CD20+ and CD8+ immune cells from the stroma and tumor compartments from multiplex-immunofluorescence (mIF) for 69 patients. TNBC subtypes were computed as described by Bareche et al. Association of continuous variables with pCR was evaluated with logistic regression (univariate analysis). Results: The pCR rates differed across TNBC subtypes (Fisher’s test, P = 0.02). In detail, pCR was achieved in 88% (8/9) of basal like (BL), 63% (17/27) of immunomodulatory (IM) and 45% (16/35) of mesenchymal (M) tumors, while lower pCR rates were observed for the mesenchymal stem-like (MSL) and luminal androgen receptor (LAR) subtypes with 37% (3/8) and 14% (1/7), respectively, suggesting differences in the sensitivity to neoadjuvant chemotherapy in line with previous reports. When considered as continuous signature scores, pCR was positively associated to BL levels (OR = 2.7, 95% CI, 1.5-4.8; False Discovery Rate [FDR] = 0.0031), and negatively associated to MSL and LAR signature levels (OR = 0.53, 95% CI, 0.32-0.87; FDR = 0.019; OR = 0.30, 95% CI, 0.12-0.74; FDR= 0.019). In addition, CD3+ cell densities in the tumor and stroma were significantly higher in IM tumors (P = 0.002 and P < 0.001), while lower levels were found in M tumors (P = 0.005, P = 0.002). Similarly, stromal CD20+ levels were higher in IM tumors (P = 0.008) and lower in M tumors (P = 0.006), suggesting a more immunosuppressive TME in the M subtype. CD8+ cells levels were not significantly different between subtypes. Conclusions: These preliminary results show relevant differences in the pCR rates among TNBC subtypes, to be confirmed on a larger series of patients and further suggesting a substantial TNBC heterogeneity regarding treatment response. Of note, preliminary mIF results suggest a differential role of the immune response across molecular subtypes. Additional analyses integrating mIF and genomic data are currently ongoing. Funding: IMI2 JU grant agreement 821558, supported by EU’s Horizon 2020 and EFPIA. Citation Format: Andrea Joaquin Garcia, Mattia Rediti, Abdelkader Benyagoub, Stéphanie Tissot, Sylvie Rusakiewicz, Robin Liechti, Flavia Marzetta, Nicolas Penel, Julio Oliveira, Jean-Charles Goeminne, Pierre Fournel, Andreia Capela, Xiaoxiao Wang, Delphine Vincent, Françoise Rothe, Marie Morfouace, Henoch Hong, Donald Jackson, Christos Sotiriou, Laurence Buisseret. Pathologic complete response rate across triple negative breast cancer subtypes in the IMMUcan study. [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 4522.

Abstract PD4-01: PD4-01 Spatial transcriptomics reveals a substantial heterogeneity in TNBC tumor and stroma compartments with potential clinical implications

Abstract Background Triple negative breast cancer (TNBC) is a heterogeneous disease characterized by at least five molecular subtypes, namely basal like (BL), immunomodulatory (IM), luminal androgen receptor (LAR), mesenchymal (M) and mesenchymal stem like (MSL), associated with distinct gene expression, genomic and tumor microenvironment (TME) profiles. Recent technological advances allow to investigate intratumor geographic heterogeneity ignored by bulk tumor analyses. Here, we deployed spatial transcriptomics (ST) to interrogate tumor and stroma compartments heterogeneity and assess its association with clinical outcome. Methods Spatial transcriptomics (Visium® Spatial Gene Expression, 10X Genomics) was performed on a retrospective series of 94 case-control TNBC samples matched for known clinic-pathological parameters with available long term outcome. Detailed morphological annotations spanning 11 histomorphological categories were performed by a breast dedicated pathologist assisted by the automated QuPath digital pathology software. Bioinformatic analyses were performed using in house pipelines. Results We investigated the distribution of each morphological category across the five TNBC molecular subtypes. We found that LAR, M and MSL, even though they had less tumor cells, had more patches of very small size (p< 0.0001). On the other hand, BL and IM had few large and dense patches. Stroma had an opposite distribution compared to tumor, with LAR and MSL being enriched with stroma (p< 00001). Tumor infiltrating lymphocytes were specific of the IM (p< 0.0001) and to a lesser extent the BL subtype. Normal structures, like fat tissue (p< 0.008), lactiferous ducts (p< 0.03) and vessels (p< 0.02), were more present in MSL and LAR. The differences between the molecular subtypes are mirrored at the level of their cell composition and tumor organization, suggesting the possibility to assess TNBC molecular subtypes from imaging data alone. At the gene expression level, spatial deconvolution analyses revealed the co-existence of tumor and stroma compartments from different TNBC subtypes within a tumor sample of a given subtype as defined by bulk tumor analysis. Interestingly, these different tumor-stroma combinations were associated with prognosis. For example, M tumors associated with MSL stroma seem to have a better prognosis than M tumors with an M stroma (p=0.001). Furthermore, spatial resolution of the gene expression identified 418 individual clusters (median 4 clusters per sample) associated with specific molecular and cellular features highlighting a substantial intra-patient heterogeneity. These clusters were further grouped into 11 ecotypes associated with distinct hallmarks and pathways, including EMT, angiogenesis, DNA repair and immune profiles revealing an important inter-patient heterogeneity beyond TNBC classification. Interestingly, 2 ecotypes were identified within the IM subtype associated with distinct clinical outcome, with ecotype 6 characterized by high EMT, mesenchymal stroma and worse prognosis (p = 0,021). Conclusion To our knowledge, this is the largest study demonstrating the substantial intra- and inter-patient heterogeneity characterizing TNBC at an unprecedented level, with differences both in tumor and stroma composition as well as spatial organization and clinical outcome. Our results hightlight the need to consider TNBC heterogeneity for patient care and future clinical development including immunotherapy. Citation Format: Xiaoxiao Wang, David Venet, Frédéric Lifrange, Denis Larsimont, Mattia Rediti, Linnea Stenbeck, David Gacquer, Floriane Dupont, Ghizlane Rouas, Matteo Serra, Joakim Lundeberg, Françoise Rothé, Christos Sotiriou. PD4-01 Spatial transcriptomics reveals a substantial heterogeneity in TNBC tumor and stroma compartments with potential clinical implications [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 PD4-01.

Abstract P1-11-06: Multi-omics profiling of HER2-low breast cancer reveals clinically relevant subgroups and therapeutic pathways

Abstract The current HER2 testing algorithm can distinguish tumors that are completely negative for HER2 (IHC 0, HER2-zero) from HER2-low tumors [low (IHC 1+) or moderate expression (IHC 2+, ISH-)]. Because HER2-zero cases have often been combined with HER2-low cases, the clinical and biological understanding of HER2-low tumors is limited. To provide complementary information and shed light on the molecular characteristics and therapeutic insights of HER2-low breast cancer, we performed this multi-omics study of hormone receptor (HR)-negative and HER2-low breast cancer, also known as HER2-low triple-negative breast cancer (TNBC), and identified three subgroups: basal-like (BSL), receptor tyrosine kinase relevant (TKR), and mesenchymal stem-like (MSL). These three subgroups had distinct features and potential therapeutic targets and were validated in external datasets. Interestingly, the TKR subgroup (which exists in both HR-positive and HR-negative breast cancer) had activated HER2 and downstream MAPK signaling. In vitro and in vivo patient-derived xenograft experiments revealed that pretreatment with tyrosine kinase inhibitor (Lapatinib or Tucatinib) could inhibit HER2-signaling and induce accumulated expression of nonfunctional HER2 via a feedback loop, resulting in increased sensitivity to sequential HER2-targeting antibody-drug conjugate DS-8201. Our findings identify clinically relevant subgroups and provide potential therapeutic strategies for the previously targetless HER2-low TNBC subtype. GRAPH ABSTRACT Highlights of characteristics of HR-negative and HER2-low breast cancer subgroups Table S1. Highlights of characteristics of HR-negative and HER2-low breast cancer subgroups. Citation Format: Lie Chen, Cui-Cui Liu, Jing-Yu Ge, Zhi-Ming Shao, Ke-da Yu. Multi-omics profiling of HER2-low breast cancer reveals clinically relevant subgroups and therapeutic pathways [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 P1-11-06.

Targeting triple-negative breast cancer: A clinical perspective.

Triple-negative breast cancer (TNBC) is a disease with often an aggressive course and a poor prognosis compared to other subtypes of breast cancer. TNBC accounts for approximately 10%-15% of all diagnosed breast cancer cases and represents a high unmet need in the field. Up to just a few years ago, chemotherapy was the only systemic treatment option for this subtype (1). To date, TNBC is considered a heterogeneous disease. One of the existing classifications is based on the analysis of mRNA expression in 587 TNBC cases, in which Lehman et al. proposed six subtypes of TNBC as follows: two basal-like (BL1 and BL2) subtypes, a mesenchymal (M) subtype, a mesenchymal stem-like (MSL) subtype, an immunomodulatory (IM) subtype, and a luminal androgen receptor (LAR) subtype (2). Later studies have demonstrated that the IM and MSL subtypes do not correlate with independent subtypes but reflect background expression by dense infiltration of tumor-infiltrating lymphocytes (TILs) or stromal cells. According to this finding, the classification of TNBC has been revised into the following four subtypes: basal 1, basal 2, LAR, and mesenchymal subtypes (3). Over the last years, several new strategies have been investigated for the treatment of patients with TNBC. Among them, immunotherapy, antibody drug conjugates, new chemotherapy agents, and targeted therapy have been and are currently being developed. The present article aims to provide an updated overview on the different treatment options that are now available or are still under investigation for patients with TNBC.

COL8A1 enhances the invasion/metastasis in MDA-MB-231 cells via the induction of IL1B and MMP1 expression

BackgroundTriple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with a high probability of metastasis and a lack of specific targets and targeted therapeutics. Previously, we have reported that COL8A1, which is highly expressed in the mesenchymal stem-like (MSL) subtype of TNBC, facilitates TNBC growth via FAK/Src activation. Furthermore, we have found that COL8A1 enhances the invasion and metastasis of MDA-MB-231 cells, classified into MSL. However, the mechanism of invasion and metastasis by COL8A1 remains unclear. Here, we investigated the biological function of COL8A1 on the invasion and metastasis of MDA-MB-231 cells. MethodsThe invasion and metastasis of MDA-MB-231 cells were evaluated using three-dimensional (3D) culture methods and xenograft mouse models. DNA microarray analysis examined the gene expression in COL8A1-overexpressing MDA-MB-231 cells and control cells. Gene expression was verified using RT-qPCR. ResultsCOL8A1-deficient cells showed little or no metastasis, whereas forced expression of COL8A1 in MDA-MB-231 cells, the MSL subtype of TNBC cell lines, significantly promoted distant metastasis after tumor resection. As with in vivo, 3D invasion assay revealed that COL8A1 increased the invasion capacity of MDA-MB-231 and Hs578T cells, classified into the MSL subtype of TNBC. DNA microarray analysis for COL8A1-overexpressing cells indicated that COL8A1 induces interleukin 1B (IL1B) and matrix metalloproteinase-1 (MMP1) expression, both of which are correlated with COL8A1 expression in the mesenchymal subtypes of TNBC, and the Kaplan–Meier plotter provided evidence that the prognosis in the MSL subtype was strongly associated with both gene expressions and COL8A1 expression. Pharmacological inhibitor treatment showed that COL8A1 regulated IL1B and MMP1 expression through a different pathway. Moreover, the knockdown of each gene expression reduced the invasion capacity of COL8A1-overexpressing MDA-MB-231 and Hs578T cells. ConclusionOur findings indicate that COL8A1-induced IL1B and MMP1 enhanced the invasion and metastasis of the MSL subtype of TNBC. Considering our previous findings that COL8A1 promotes tumor growth, COL8A1 may be a prognostic and practical therapeutic target in TNBC.

Identification of a minimum number of genes to predict triple-negative breast cancer subgroups from gene expression profiles

BackgroundTriple-negative breast cancer (TNBC) is a very heterogeneous disease. Several gene expression and mutation profiling approaches were used to classify it, and all converged to the identification of distinct molecular subtypes, with some overlapping across different approaches. However, a standardised tool to routinely classify TNBC in the clinics and guide personalised treatment is lacking. We aimed at defining a specific gene signature for each of the six TNBC subtypes proposed by Lehman et al. in 2011 (basal-like 1 (BL1); basal-like 2 (BL2); mesenchymal (M); immunomodulatory (IM); mesenchymal stem-like (MSL); and luminal androgen receptor (LAR)), to be able to accurately predict them.MethodsLehman’s TNBCtype subtyping tool was applied to RNA-sequencing data from 482 TNBC (GSE164458), and a minimal subtype-specific gene signature was defined by combining two class comparison techniques with seven attribute selection methods. Several machine learning algorithms for subtype prediction were used, and the best classifier was applied on microarray data from 72 Italian TNBC and on the TNBC subset of the BRCA-TCGA data set.ResultsWe identified two signatures with the 120 and 81 top up- and downregulated genes that define the six TNBC subtypes, with prediction accuracy ranging from 88.6 to 89.4%, and even improving after removal of the least important genes. Network analysis was used to identify highly interconnected genes within each subgroup. Two druggable matrix metalloproteinases were found in the BL1 and BL2 subsets, and several druggable targets were complementary to androgen receptor or aromatase in the LAR subset. Several secondary drug–target interactions were found among the upregulated genes in the M, IM and MSL subsets.ConclusionsOur study took full advantage of available TNBC data sets to stratify samples and genes into distinct subtypes, according to gene expression profiles. The development of a data mining approach to acquire a large amount of information from several data sets has allowed us to identify a well-determined minimal number of genes that may help in the recognition of TNBC subtypes. These genes, most of which have been previously found to be associated with breast cancer, have the potential to become novel diagnostic markers and/or therapeutic targets for specific TNBC subsets.

1711P Spatial transcriptomics reveals substantial heterogeneity in TNBC tumor and stroma compartments with potential clinical implications

Triple negative breast cancer (TNBC) is a heterogeneous disease characterized by at least five molecular subtypes, namely basal like (BL), immunomodulatory (IM), luminal AR (LAR), mesenchymal (M) and mesenchymal stem like (MSL), associated with distinct gene expression, genomic and tumor microenvironment (TME) profiles. Recent technological advances allow to investigate intratumor geographic heterogeneity ignored by bulk tumor analyses. Here, we deployed spatial transcriptomics (ST) to interrogate tumor and stroma compartments heterogeneity and assess its association with clinical outcome. Spatial transcriptomics was performed on a series of 94 case-control TNBC samples matched for known clinic-pathological parameters. Detailed morphological annotations spanning 11 histomorphological categories were performed by a breast dedicated pathologist assisted by the automated QuPath digital pathology software. Bioinformatics analyses were performed using in house pipelines. Morphologically, LAR, M and MSL tumors were more diffused and surrounded by more stroma, as compared to BL and IM TNBCs displaying large tumor patches with higher immune infiltration. Indeed, overall, LAR and MSL tumors were more enriched in stroma, fat tissue and vessels. Spatial gene expression analysis identified 418 individual clusters, which were grouped to define 11 ecotypes (i.e. cluster combinations) associated with specific molecular and cellular features, including EMT, angiogenesis, DNA repair and immune profiles. In particular, we identified 2 ecotypes (6 and 8) within the IM subtype with distinct clinical outcomes, with the ecotype 6 associated with EMT and mesenchymal stroma having worse prognosis (p = 0,021). To our knowledge, this is the largest study demonstrating at an unprecedented level the substantial intra- and inter-patient heterogeneity characterizing TNBC, with regards to morphology, as well as molecular and cellular features. Our results hightlight the need to consider TNBC heterogeneity for future clinical development and patients’ care.

Abstract 2647: RVU120, a selective CDK8/CDK19 inhibitor, demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo

Abstract Breast cancer (BC) is a complex and heterogenous disease, and various approaches have been used to classify BC into several subtypes to improve diagnostic and therapeutic outcomes. One of the features of BC is deregulated transcription, which allows for classification of the disease based on gene expression signature into four basic types: Luminal A, Luminal B, HER2-enriched, and triple negative (TNBC)/basal-like. Novel therapeutic approaches targeting oncogenic transcriptional programs may represent a promising strategy, in particular for TNBC, where the lack of common genetic alterations has so far limited the development of targeted therapies. The CDK8 module functions as a master coordinator of transcription, bridging enhancers and core promoters. Meta-analysis of curated TCGA data reveals that >15% of all BC have increased expression of CDK8 and/or CDK19, and that elevated expression of both genes is associated with decreased overall survival. High CDK8 expression is inversely correlated with the expression of estrogen receptor (ER) and positively correlated with occurrence of TP53 mutations. RVU120 is a specific, low nM, selective inhibitor of CDK8/CDK19, currently being tested in a first-in-human Phase Ib clinical trial in patients with metastatic or advanced solid tumors progressing from previous lines of therapy (ClinicalTrials.gov: NCT05052255). In order to establish a rationale for treatment of BC with RVU120 we have interrogated a panel of cell lines representing various subtypes of BC. These studies revealed that TNBC and ER-/PR-/HER2+ cells were highly sensitive to RVU120 and also to two other non-related CDK8/19 inhibitors, indicating a class effect. In contrast, CDK8/19 inhibitors were not able to inhibit mitogenic effect of estrogen, confirming differential efficacy in hormone - independent BC. Detailed transcriptional profiling of RVU120-responder cells revealed high enrichment of STAT3 target genes, SOX4 target genes and gene hallmarks of epithelial to mesenchymal transition (EMT), signatures associated with invasiveness and stemness. Non-responder cells were characterized by enrichment of transcriptional signatures of ER activity. Further proteomic profiling show that the top responder cells were the Mesenchymal Stem-Like (MSL) molecular subtype of TNBC and were positive for transactivated pSTAT3. Transcriptomic RNAseq profiling of MSL TNBC cell lines indicated that among genes inhibited by RVU120 there was high enrichment of STAT1 (interferon signature), STAT3 (IL6- signaling) and STAT5 (IL2 signaling) dependent genes. Single agent efficacy of RVU120 has been confirmed in subcutaneous TNBC xenograft models in vivo at well tolerated doses. Overall, these studies provide rationale for further development of RVU120 in TNBC patients. Citation Format: Urszula Pakulska, Marta Obacz, Aniela Gołas, Milena Mazan, Magdalena Masiejczyk, Agata Stachowicz, Justyna Martyka, Michał Combik, Kinga Kęska, Katarzyna Wiklik, Kristina Goller, Elżbieta Adamczyk, Krzysztof Brzózka, Tomasz Rzymski. RVU120, a selective CDK8/CDK19 inhibitor, demonstrates efficacy against hormone-independent breast cancer cells in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2647.

Abstract CT131: RVU120 SOL-021: An open-label, single agent, phase I/II trial of RVU120 (SEL120) in patients with relapsed/refractory metastatic or advanced solid tumors

Abstract Background: CDK8 and its paralog CDK19 have central roles in maintenance of cancer cell viability and undifferentiated state for a variety of tumor types. (Dannappel et al. 2019; Rzymski et al. 2015; Philip et al. 2018). CDK8 and CDK19 work by incorporating in a mutually exclusive manner, into a Mediator kinase module, that reversibly associates with a protein complex regulator of RNA Polymerase II, to mediate gene transcription. Targeting cancer-specific gene transcription via CDK8/19 inhibition has potential for treatment of solid tumors. RVU120 (SEL120) is a selective CDK8/19 inhibitor with preclinical efficacy in hematologic malignancies and a variety of solid tumor types (Rzymski et al. 2017). RVU120 showed strong anticancer activity in preclinical triple-negative breast cancer (TNBC) models, especially in the mesenchymal stem-like (MSL) molecular subtype (Rzymski et al SABCS 2021). Methods: SOL-021 is a Phase I/II clinical trial of RVU120 in Patients with metastatic or advanced solid tumors, who have exhausted available treatments, currently ongoing in Poland and Spain under NCT05052255 clinical trial register number. RVU120 is administered as single oral dose every other day (QOD) for a total of 7 doses on Days 1, 3, 5, 7, 9, 11 and 13, in a 3-week treatment cycle until progression or unacceptable toxicity. The study is designed in 2 parts: Part 1 follows a 3+3 dose escalation design and has primary objectives to characterize the safety and tolerability of RVU120 (SEL120) as single agent in patients with different tumors types and determination of the RP2D. Secondary objectives include objective response rate (ORR) according to RECIST criteria v1.1, duration of response (DoR), disease-control rate, progression-free survival (PFS), overall survival (OS) and pharmacokinetic profile of RVU120.Part 2 will primarily explore the anti-tumor activity of RVU120 as single agent in different patient populations. Based on strong preclinical evidence of anticancer activity of RVU120 on TNBC cells (Tomasz Rzymski SABCS #1766), patients with relapsed/refractory TNBC will be enrolled. Additionally, relapsed/refractory patients agnostic of their solid tumor type and selected based on their biomarker profile will be enrolled. The total duration of the study is approximately 27 months (12 and 15 for part 1 and 2, respectively). Results: At 11 Feb 2022 data cut off, 5 patients have been enrolled in part 1 of the study and no SAE have been observed: First cohort, 75 mg, was closed on 24 Nov 2021 with no DLT observed; current ongoing cohort, 100 mg dose level, is expected to be closed in the upcoming week, and subsequent cohort, 125 mg, to be opened mid-March. Conclusion: The trial is continuing as planned; the next data analysis will occur first week of March 2022. Citation Format: Rafal Dziadziuszko, Elena Garralda, Noemi Angelosanto, Tomasz Rzymski, Renata Dudziak, Krzysztof Brzózka, Peter Littlewood, Hendrik Nogai, Axel Glasmacher, Iwona Lugowska. RVU120 SOL-021: An open-label, single agent, phase I/II trial of RVU120 (SEL120) in patients with relapsed/refractory metastatic or advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT131.

Abstract LB085: ATYR2810, a fully humanized monoclonal antibody targeting the VEGF-NRP2 pathway sensitizes highly aggressive and chemoresistant TNBC subtypes to chemotherapy

Abstract Introduction: Triple negative breast cancer (TNBC) represents 15% of all breast cancers, and is a notably aggressive subtype that is prone to early recurrence following initial diagnosis with a median survival of only 9 months following recurrence. One of the few treatment options for patients with advanced and metastatic TNBC is platinum-based chemotherapy, however not all tumors respond, and those that do often become refractory during the course of treatment. The cell surface receptor Neuropilin-2 (NRP2), which acts as a co-receptor for vascular endothelial growth factors (VEGFs), has been shown to be both highly expressed and associated with therapeutic resistance in TNBC. NRP2 also serves as a co-receptor for semaphorins, which may play tumor-suppressor functions in breast cancer. We have previously demonstrated that ATYR2810, a highly specific humanized monoclonal antibody which effectively blocks NRP2/VEGF signaling without disrupting NRP2/Semaphorin 3F signaling, down-regulated epithelial-mesenchymal transition (EMT) genes such as ZEB1 and sensitizes TNBC to chemotherapy both in vitro and in vivo. Results: In this study we have further characterized the breast cancer subtypes that are most responsive to ATYR2810 treatment. Using in vitro 3D colony formation assays (CFAs), we have interrogated ~15 breast cancer cell lines covering luminal, HER2+ and various TNBC subtypes, for responsiveness to ATYR2810 treatment in combination with chemotherapy. All responsive cell lines were associated with the more aggressive subtypes of TNBC such as BL2 (basal-like 2), ML (mesenchymal-like) and MSL (mesenchymal-stem like) subtypes. Additionally, we screened five patient derived xenografts (PDXs) and again found that the responsive PDXs were associated with the more aggressive and chemoresistant subtypes of TNBC. To gain insight into the potential mechanism for enhanced chemosensitivity by ATYR2810 treatment, we performed RNAseq on the PDX tumors. Interestingly, the chemokine receptor CXCR4, which is known to promote drug resistance and tumorigenic potential, was found to be significantly downregulated in responder PDX tumors treated with ATYR2810 in combination with cisplatin as compared to those treated with cisplatin alone. Further, gene set enrichment analysis (GSEA) showed that CXCR4 was found in numerous downregulated pathways enriched in the PDX responder tumors treated with ATYR2810/cisplatin, suggesting that CXCR4 may be driving the responder phenotype of the PDXs. Flow cytometry analysis of TNBC cells treated with ATYR2810 monotherapy in vitro resulted in a reduced frequency of cells expressing CXCR4. Furthermore, ATYR2810 monotherapy inhibited spontaneous lung metastasis in experimental models of mesenchymal TNBC. Conclusion: Taken together, our data suggest that ATYR2810 enhances chemosensitivity in highly aggressive TNBC subtypes, and that this response may be mediated through the downregulation of genes known to be associated with aggressive cancer states such as ZEB1 and CXCR4. ATYR2810 may therefore serve as a novel therapeutic agent for the treatment of advanced and metastatic TNBC and potentially other aggressive cancer types. Zhiwen Xu and Alison Barber are co-first authors of this abstract. Citation Format: Zhiwen Xu, Alison Barber, Christoph Burkart, Hira Lal Goel, Justin Rahman, Kristina Hamel, Zachary Fogassy, Lisa Eide, Clara Polizzi, Jasmine Stamps, Sofia Klopp Savino, Luke Burman, Esther Chong, Suzanne Paz, Arthur M. Mercurio, Leslie A. Nangle. ATYR2810, a fully humanized monoclonal antibody targeting the VEGF-NRP2 pathway sensitizes highly aggressive and chemoresistant TNBC subtypes to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB085.

Phase I/II trial of RVU120 (SEL120), a CDK8/CDK19 inhibitor in patients with relapsed/refractory metastatic or advanced solid tumors.

e15091 Background: CDK 8 /CDK19 are kinases involved in transcriptional control of embryonic development and cellular homeostasis via the mediator complex. They are also described to maintain tumor dedifferentiation and stem cell properties. A variety of cancer cells hijack the mediator complex and targeting cancer-specific gene transcription via CDK8/19 inhibition has potential for treatment of solid tumors. RVU120 (SEL120) is a selective CDK8/19 inhibitor with preclinical efficacy in hematologic malignancies and a variety of solid tumor types (Rzymski et al. 2017). RVU120 showed strong anticancer activity in preclinical triple-negative breast cancer (TNBC) models, especially in the mesenchymal stem-like (MSL) molecular subtype (Rzymski et al SABCS 2021). Methods: A Phase I/II clinical trial of RVU120 in solid tumors is currently ongoing (NCT05052255). Patients with metastatic or advanced solid tumors without available treatments receive increasing doses of RVU120 as a single oral dose every other day (QOD) for a total of 7 doses on Days 1, 3, 5, 7, 9, 11 and 13, in a 3-week treatment cycle. Primary objectives of the study are safety / tolerability of RVU120 as single agent and determination of the recommended Phase II dose (RP2D) via a 3+3 dose escalation design. Secondary objectives include objective response rate (ORR) (RECIST criteria v1.1) and PK of RVU120. Results: As of 11FEB 2022, 5 pts have been enrolled into the trial: 3 into cohort 1, 75 mg dose, 2 into cohort 2, 100 mg. None of the pts experienced a DLT, SAEs or > Grade 3 AE. Treatment-related AEs were all G1 except for G2 diarrhea and weakness. Cohort 1 patients had at least 1 post-baseline tumor assessment. A 62 YO patient, stage IV esophago-gastric junction carcinoma, metastases to the liver, retroperitoneum, adrenal gland and portocaval lymph nodes, progressing after 4 lines of previous therapy, achieved a SD with a +4% change of target lesion size and progressed in cycle 6. A 65 YO patient, stage IV adenoid cystic carcinoma of the trachea, metastases to the lung and refractory to antiandrogens and radiotherapy, achieved a SD with -4% change of target lesion size after 3 cycles and is currently ongoing in cycle 5. A 43 YO pt stage IV thymic carcinoma, metastases to the lung, mediastinum, pleura and lymph nodes, progressing under cisplatin/etoposide, stopped study drug at the end of cycle 3 for PD in non-target lesions, target lesions increased by 11%. Cohort 2 patients, a 65 YO pt with pancreatic cancer stage IV, metastases to liver and lung, and a 55 YO pt with TNBC stage IV, metastases to the lung, will be evaluated end of cycle 3. Conclusions: In the first dose escalation level with single agent RVU120, no DLTs or ≥G3 AEs were observed in patients with previously progressive solid tumors. Initial assessments in 3 pts demonstrated stable disease in 2 patients. Collection of further data at higher doses is ongoing with 2 patients enrolled at 100 mg. Clinical trial information: NCT05052255.

Tocilizumab overcomes chemotherapy resistance in mesenchymal stem-like breast cancer by negating autocrine IL-1A induction of IL-6

Triple-negative breast cancer (TNBC) patients with mesenchymal stem-like (MSL) subtype have responded poorly to chemotherapy whereas patients with basal-like 1 (BL1) subtype achieved the best clinical response. In order to gain insight into pathways that may contribute to the divergent sensitivity to chemotherapy, we compared the inflammatory profile of the two TNBC subtypes treated with docetaxel. Cellular signaling analysis determined that docetaxel activated MAPK pathway in MSL TNBCs but not BL1 TNBCs. The subsequent MAPK pathway activation in MSL TNBCs led to an IL-1A mediated cascade of autocrine inflammatory mediators including IL-6. Utilizing the humanized IL-6R antibody, tocilizumab, our in vitro and in vivo data show that MSL TNBCs treated with tocilizumab together with chemotherapy results in delayed tumor progression compared to MSL TNBCs treated with docetaxel alone. Our study highlights a molecular subset of TNBC that may be responsive to tocilizumab therapy for potential translational impact.

Immune Milieu and Genomic Alterations Set the Triple-Negative Breast Cancer Immunomodulatory Subtype Tumor Behavior.

Simple SummaryTriple-negative breast cancer (TNBC) is an aggressive and highly heterogeneous breast cancer subtype, both molecular and transcriptomic. Gene expression patterns identified seven TNBC subtypes; basal-like 1 (BL1), basal-like 2 (BL2), immunomodulatory (IM), mesenchymal (M), mesenchymal stem-like (MSL), luminal androgen receptor (LAR), and unstable (UNS). Herein, we contrasted the IM subtype with non-IM TNBC, including clinical, histopathological, and molecular variables. Our results showed that the IM subtype featured an increased FOXP3+ TILs infiltration and a higher CTLA-4 and PD-L1 expression compared with non-IM tumors. Long intergenic non-coding RNAs associated with the immune response through transcriptomic and enrichment analyses characterized the IM-subtype enriched by the β-catenin signaling pathway. Additionally, DNA sequencing identified differences in mutation rates as well as some specific mutations. These results should motivate the design of future clinical trials in which the benefit of immune-based therapy in this subgroup of patients could be evaluated.Triple-negative breast cancer (TNBC) is an aggressive and heterogeneous disease. Seven subtypes have been described based on gene expression patterns. Herein, we characterized the tumor biology and clinical behavior of the immunomodulatory (IM) subtype. Methods: Formalin-fixed paraffin-embedded tumor samples from 68 high-risk (stage III-IV) TNBC patients were analyzed through microarrays, immunohistochemistry, and DNA sequencing. Results: The IM subtype was identified in 24% of TNBC tumor samples and characterized by a higher intratumoral (intT) and stromal (strml) infiltration of FOXP3+ TILs (Treg) compared with non-IM subtypes. Further, PD-L1+ (>1%) expression was significantly higher, as well as CTLA-4+ intT and strml expression in the IM subtype. Differential expression and gene set enrichment analysis identified biological processes associated with the immune system. Pathway analysis revealed enrichment of the β-catenin signaling pathway. The non-coding analysis led to seven Long Intergenic Non-Protein Coding RNAs (lincRNAs) (6 up-regulated and 1 down-regulated) that were associated with a favorable prognosis in the TNBC-IM subtype. The DNA sequencing highlighted two genes relevant to immune system responses: CTNNB1 (Catenin β-1) and IDH1. Conclusion: the IM subtype showed a distinct immune microenvironment, as well as subtype-specific genomic alterations. Characterizing TNBC at a molecular and transcriptomic level might guide immune-based therapy in this subgroup of patients.

Abstract 175: Pathway modeling to translate the 27-gene immuno-oncology algorithm into bladder cancer

Abstract Background The 27-gene immuno-oncology (IO) algorithm has demonstrated an association with immune checkpoint inhibitor (ICI) response in TNBC, NSCLC, and metastatic urothelial carcinoma (mUC). The algorithm can be run on data generated from either a qPCR assay or from analysis of whole transcriptome RNA-seq data. It integrates gene expression information from infiltrating inflammatory cells with signatures from surrounding stroma and tumor cells to classify cases into likely responder versus non-responders. We hypothesized that because the algorithm derives its biologic signature from the tumor immune microenvironment (TIME), the classification function and thresholds might translate to other solid tissue types based upon biologic separation of inflammatory phenotypes. Methods Using NSCLC and breast cancer datasets from TCGA, we identified 939 genes that comprise the Mesenchymal (M), Mesenchymal Stem-like (MSL), and Immunomodulatory (IM) gene expression patterns centered around a previously described 101-gene signature (Ring, 2016). We applied this 939 gene set to 433 bladder samples from TCGA (UC) and k-means clustered the genes based upon each of the three centroids. Clinical cases were also organized by k-means clustering (k=3). Pathway analysis was performed (GSEA—UCSD/Broad). We assessed classification of UC cases by looking at enrichment of inflammatory pathways into the IM cluster compared to mesenchymal pathways into the M or MSL clusters. The threshold for responder classification using the 27-gene IO algorithm previously established in TNBC was assessed by quantitating the fraction of cases enriched into the IM cluster (potential responders) as opposed to the M or MSL clusters (potential non-responders). Results The 939 genes centered around the 101-gene signature encoded twenty different physiologic pathways. Ten of these pathways included at least one of the genes from the 27-gene IO algorithm. Significant enrichment of inflammatory cell pathways was seen into the IM cluster as opposed to mesenchymal and reactive fibroblast pathways enriched into the M and MSL clusters. Pathways containing therapeutic targets designed to overcome resistance to ICIs were enriched in the MSL gene expression centroid. The 27-gene IO algorithm threshold applied to the TCGA samples classified 79% as responders in the IM cluster as opposed 16% in the M and MSL. Discussion These results support the hypothesis that gene expression signatures discerning TIME physiology associated with ICI response are tissue agnostic and relevant in multiple solid tissue types. The dramatic enrichment of responders into the IM cluster using previously established thresholds is consistent with appropriate biologic classification of the cases and supports utilizing the 27-gene IO algorithm and established threshold for association with ICI response in treated mUC cohorts. Citation Format: Robert S. Seitz, Tyler J. Nielsen, Brock L. Schweitzer, David R. Hout, Douglas T. Ross. Pathway modeling to translate the 27-gene immuno-oncology algorithm into bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 175.

Abstract 609: Contribution of the tumor and stroma compartments for TNBC molecular classification using spatial transcriptomics analysis

Abstract Introduction Triple negative breast cancer (TNBC) is a heterogeneous disease associated at least with five distinct molecular subtypes namely basal like (BL), immunomodulatory (IM), luminal AR (LAR), mesenchymal (M) and mesenchymal-stem like (MSL). Spatial transcriptomics (ST) interrogates gene expression in spatially defined spots. Here, we aimed to assess the contribution of tumor and stroma compartments in defining each TNBC molecular subtype by comparing bulk tumor RNAseq, pseudo-bulk (PB) derived from ST, tumor and stroma ST spots. Methods Spatially resolved gene expression profiles were obtained from 94 TNBC samples using ST, spots with artifacts or less than 500 reads being excluded from further analysis. Forty-one TNBC samples were manually annotated by a breast pathologist into 3 different classes: tumor, stroma and the rest. Manual histological annotation was used to build a classifier to assign each ST spot to tumor or stroma compartment. Bulk RNAseq data was obtained from consecutive sections for all tumors using RiboZero kit. PB profiles were obtained by summing the reads from all the spots of a given tumor, as well as from all spots classified as tumor and stroma compartment. A linear booster classifier was used to classify the spots based on gene expression. Each bulk and PB was assigned to one of 5 TNBC molecular subtypes. Results PB data derived from ST analysis identified 18 BL, 26 IM, 10 LAR, 27 M and 13 MSL among the 94 TNBC tumor samples. An 87% concordance in the subtyping was observed between the bulk and PB data, with half of the discordant cases being between BL and IM subtypes. All LAR and BL tumors, as well as most M (96%) were consistently classified using tumor spots only whereas all MSL (100%) and the majority of LAR (91%) and IM (92%) samples were concordant using stroma spots only. In half of the IM samples, the signal derived from both the tumor and the stroma compartments while in the other half derived from the stroma. Misclassification mainly occurred between BL and IM subtypes, as well as between M and MSL. LAR subtype appeared to be the most stable one. Conclusion The use of spatial transcriptomics allowed to show the relative contribution of the tumor and stroma compartments for TNBC molecular classification. The LAR, BL and M subtypes were driven by signals from the tumor compartment while MSL was driven by the stroma compartment. The IM signal was derived by both the tumor and stroma compartments. Citation Format: David Venet, Xiaoxiao Wang, Floriane Dupont, Ghizlane Rouas, Linnea Stenbeck, Annelie Mollbrink, Denis Larsimont, Joakim Lundeberg, Françoise Rothé, Christos Sotiriou. Contribution of the tumor and stroma compartments for TNBC molecular classification using spatial transcriptomics analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 609.

Association with immune checkpoint inhibitor efficacy of a 27-gene classifier in renal cell cancer.

4575 Background: The 27-gene immuno-oncology (IO) signature that incorporates expression from activated inflammatory cells, cancer associated fibroblasts, and tumor cells to produce a binary classifier has been shown to be associated with efficacy to immune checkpoint inhibitors (ICIs) in breast, lung, and bladder cancers. Here we created clustered heat maps using data from The Cancer Genome Atlas (TCGA) to confirm the classifier function and diagnostic threshold in renal cell carcinoma (RCC), then applied the predefined algorithm to RNAseq data from a community RCC cohort treated with ICI therapy. Methods: Previously, we described the selection of 939 genes from the TCGA breast and lung datasets that comprise mesenchymal (M), mesenchymal stem-like (MSL), and immunodulatory (IM) gene expression patterns centered upon the twenty-seven genes selected for the IO score (AACR, 2021). We created an expression dataset using these genes in clear cell (n = 403) and papillary (n = 203) RCC and used k-means clustering to organize the genes and cases (k=3). We assessed the 27-gene classification of cases by utilizing area under the curve for phenotypic classification and determining the sensitivity and specificity of the previously established threshold compared to optimal accuracy for quantitating the fraction of cases enriched into the IM+ cluster (likely sensitive to ICIs) as opposed to the M or MSL clusters (likely insensitive). Finally, the IO score was evaluated in a small multi-institutional RNAseq dataset of forty-three RCC patients treated with an ICI for which there was definitive one-year progression free survival (PFS) data. Results: The 27-gene IO signature applied to the TCGA sample data had an AUC of 90.3 for stratification of cases into IM+ as opposed to M and MSL clusters while the established threshold for likely sensitive enriched 90% of cases into the appropriate IM cluster as opposed 28% into the M and MSL. Efficacy was defined by PFS. Given this result, the 27-gene IO signature was applied with the predefined threshold to the forty-three ICI treated patients. Patients who had a IO+ score by the 27-gene signature had significantly better one-year PFS compared to patients with a negative IO score (hazard ratio = 0.235, 95% CI = 0.069 - 0.803, p < 0.01). Median PFS was 5.2 months for patients classified as IO score negative versus 8.6 months for those classified as IO score+. Conclusions: The 27-gene IO signature has been validated across multiple tumor types and here in RCC to classify the tumor immune microenvironment without changing the algorithm or threshold. Results demonstrate that the 27-gene classifier has a strong correlation with efficacy of ICI therapy in RCC. This is the fourth tumor type in which the same algorithm has been validated as a predictor of ICI efficacy. These data support this assay as a strong pan-cancer immune system classifier worthy of further prospective study for ICI therapy.

Dual Inhibition of AKT and MEK Pathways Potentiates the Anti-Cancer Effect of Gefitinib in Triple-Negative Breast Cancer Cells.

Simple SummaryTriple-negative breast cancer (TNBC) is an intractable subset of breast cancer without an efficient therapeutic strategy due to the lack of tractable targets, such as the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Activation and/or amplification of epidermal growth factor receptor (EGFR), phosphoinositide 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog (AKT), and MAPK/ERK kinase (MEK)/ extracellular signal-regulated kinase (ERK) pathways is known in TNBC; however, interventions for these targets have not been successful to date. To explore a combinatorial strategy with existing clinical/preclinical protein kinase inhibitors (PKIs) in TNBC cells, we performed a series of cytotoxicity (cell viability) screenings with various PKIs in the presence figure of an EGFR inhibitor, gefitinib. The dual inhibition of AKT and MEK with gefitinib reduced the proliferation and colony formation of TNBC cells by inducing apoptosis. Our finding suggests a new approach for treating TNBC with a multiplex combination of PKIs.There is an unmet medical need for the development of new targeted therapeutic strategies for triple-negative breast cancer (TNBC). With drug combination screenings, we found that the triple combination of the protein kinase inhibitors (PKIs) of the epidermal growth factor receptor (EGFR), v-akt murine thymoma viral oncogene homolog (AKT), and MAPK/ERK kinase (MEK) is effective in inducing apoptosis in TNBC cells. A set of PKIs were first screened in combination with gefitinib in the TNBC cell line, MDA-MB-231. The AKT inhibitor, AT7867, was identified and further analyzed in two mesenchymal stem-like (MSL) subtype TNBC cells, MDA-MB-231 and HS578T. A combination of gefitinib and AT7867 reduced the proliferation and long-term survival of MSL TNBC cells. However, gefitinib and AT7867 induced the activation of the rat sarcoma (RAS)/ v-raf-1 murine leukemia viral oncogene homolog (RAF)/MEK/ extracellular signal-regulated kinase (ERK) pathway. To inhibit this pathway, MEK/ERK inhibitors were further screened in MDA-MB-231 cells in the presence of gefitinib and AT7867. As a result, we identified that the MEK inhibitor, PD-0325901, further enhanced the anti-proliferative and anti-clonogenic effects of gefitinib and AT7867 by inducing apoptosis. Our results suggest that the dual inhibition of the AKT and MEK pathways is a novel potential therapeutic strategy for targeting EGFR in TNBC cells.

Abstract PS7-12: Impact of race/ethnicity on triple negative breast cancer molecular features, treatment response and clinical outcomes in patients receiving neoadjuvant therapy

Abstract Background: Triple negative breast cancer (TNBC) disproportionally impacts Black and Hispanic women and is suggested to be partly responsible for disparities observed in breast cancer mortality. We sought to evaluate the impact of race/ethnicity on TNBC molecular subtype, immune profile, pathologic complete response (pCR) and recurrence free survival (RFS). Methods: The ARTEMIS trial (NCT02276443) uses imaging response and molecular profiling to personalize neoadjuvant chemotherapy in early stage TNBC. After 4 cycles of AC, patients with chemo-sensitive disease receive standard taxane-based therapy, while those with chemo-resistant disease are offered therapeutic trials based upon molecular profiling. Pathologic response was assessed at surgery. Patients self-reported race/ethnicity was categorized as Asian, Black/African-American, Hispanic/Latino and White (non-Hispanic). Patients were excluded if no race or ethnicity was reported. Clinical and pathologic factors were recorded and compared. Gene expression profiling was performed by RNAseq to determine Vanderbilt signature. PD-L1 and Androgen Receptor (AR) were determined by immunohistochemistry. Frequencies at which various factors were observed by race/ethnicity were calculated and Fisher’s exact test performed to determine statistical significance. Kaplan-Meier analysis was used to estimate survival stratified by pCR status and race/ethnicity. Results: Among 321 women enrolled in ARTEMIS, 26 (8.1%) were classified as Asian, 50 (15.6%) as Black, 59 (18.4%) as Hispanic and 186 (57.9%) as White. Demographic and clinical features were similar, except Black women were more likely to have BMI ≥30 (70.0%, p<0.001). Comparing by race/ethnicity, there was no statistically significant difference in tumor histology, tumor size, nodal status, clinical stage, chemo-resistant disease, type of surgery or receipt of radiation. A trend toward higher proportion of N3 disease was observed in Black women (24.0%) compared to other groups (p=0.054). Tumor profiling results are listed in Table 1. No statistically significant difference was observed by race/ethnicity in Vanderbilt signature, presence of PD-L1 or stromal tumor infiltrating lymphocytes (sTIL) status. More AR-positive tumors were identified in Asian women (64%, p=0.007). pCR and RCB status did not significantly vary by race/ethnicity however, higher proportion of RCB-III disease was identified in Black (14%) and Hispanic women (16.9%) as compared to Asian (3.8%) and White (8.6%) women (p=0.164). At median follow up of 23.8 months (range 3.4-51.1), there was no statistically significant difference in RFS by race/ethnicity. Conclusion: Among this population of patients with TNBC treated with neoadjuvant chemotherapy there was no statistically significant difference observed in TNBC Vanderbilt signature, PD-L1 staining, sTIL, pCR or RFS by race/ethnicity. Asian women were found to have a higher incidence of AR-positive subtype. Numerically higher rates of N3 stage in Black women and RCB-III classification in Black and Hispanic women were identified, however not statistically significant. Larger cohorts of patients are needed to further investigate these findings. Table 1. TNBC profiling compared by race/ethnicity.Total n (%)Asian n (%)Black n (%)Hispanic/Latino n (%)White n (%)p valueVanderbilt signature n (%) Basal like (BL1) Basal like 2 (BL2) Immunomodulatory (IM) Luminal androgen receptor (LAR) Mesenchymal (M) Mesenchymal stem-like (MSL) Unstable (UNS)231 50 (21.6) 25 (10.8) 42 (18.2) 22 (9.5) 48 (20.8) 14 (6.0) 30 (13.0)21 (9.1) 0 (0.0) 4 (19.0) 5 (23.8) 3 (14.3) 5 (23.8) 1 (4.8) 3 (14.3)35 (15.2) 9 (25.7) 5 (14.3) 6 (17.1) 2 (5.7) 7 (20.0) 1 (2.9) 5 (14.3)43 (18.6) 14 (32.5) 3 (7.0) 10 (23.2) 5 (11.6) 6 (14.0) 2 (4.7) 3 (7.0)132 (57.1) 27 (20.5) 13 (9.8) 21 (15.9) 12 (9.1) 30 (22.7) 10 (7.6) 19 (14.4)NSAndrogen Receptor n (%) Positive (>=10%) Negative (<10%)311 109 (35.0) 202 (65.0)25 (8.0) 16 (64.0) 9 (36.0)49 (15.8) 11 (22.4) 38 (77.6)57 (18.3) 19 (33.3) 38 (66.7)180 (57.9) 63 (35.0) 117 (65.0)0.007PD-L1 n (%) None >1298 212 (71.1) 86 (28.9)24 (8.1) 15 (62.5) 9 (37.5)47 (15.8) 33 (70.2) 14 (29.8)57 (19.1) 40 (70.2) 17 (29.8)170 (57.0) 124 (72.9) 46 (27.1)NSStromal tumor infiltrating lymphocytes (sTIL) n (%) High (>=20%) Low (<20%)319 107 (33.5) 212 (66.5)26 (8.1) 12 (46.2) 14 (53.8)50 (15.7) 13 (26.0) 37 (74.0)58 (18.2) 21 (36.2) 37 (63.8)185 (58.0) 61 (33.0) 124 (67.0)NS Citation Format: Mediget Teshome, Ryan Sun, Elizabeth E. Ravenberg, Abenaa Brewster, Mariana Chavez-MacGregor, Jason B. White, Stacy Moulder. Impact of race/ethnicity on triple negative breast cancer molecular features, treatment response and clinical outcomes in patients receiving neoadjuvant therapy [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-12.