Non-metastatic Triple-negative Breast Cancer Research Articles

TOWARDS Study: Patient-Derived Xenograft Engraftment Predicts Poor Survival in Patients With Newly Diagnosed Triple-Negative Breast Cancer.

Assessing risk of recurrence for nonmetastatic triple-negative breast cancer (TNBC) is a key determinant of therapeutic strategy. The best predictor of recurrence risk is failure to achieve a pathologic complete response after preoperative chemotherapy, but it imperfectly correlates with the definitive end points of relapse-free and overall survival (OS). The inability to accurately predict recurrence has led to increasingly toxic treatment regimens for patients with early-stage TNBC. Better assays for recurrence risk are needed to tailor aggressive therapy for patients who need it and avoid overtreatment and unnecessary toxicity for those at low risk. The purpose of this study was to determine if patient-derived xenograft (PDX) engraftment of newly diagnosed breast tumors can serve as an accurate predictor of recurrence and death from breast cancer. This study was a blinded noninterventional trial comprising 80 patients with newly diagnosed, nonmetastatic, estrogen receptor (ER)-negative or ER-low breast cancer. PDX engraftment was strongly associated with relapse in 1 year: 8 of 18 (44.4%) patients whose tumors engrafted relapsed versus 1 of 62 (1.6%) patients whose tumors did not engraft (P < .0001). Patients whose tumors engrafted had a hazard ratio (HR) for relapse of 17.5. HRs for OS and breast cancer-specific survival in PDX+ patients were 21.1 and 39.5, respectively. We report that the ability of a tumor to engraft as a PDX predicts early recurrence by serving as a functional readout of aggressiveness and prospectively identifies the most devastating tumors. This provides new opportunity to develop surrogate assays, such as biomarkers of engraftment, which will extend the clinical feasibility of this finding.

Tolerance and safety of adjuvant metronomic capecitabine in Indian patients with non-metastatic triple negative breast cancer (TNBC): An institutional experience.

e12530 Background: Triple-negative breast cancer (TNBC) subtype has a high risk of recurrence and overall poorer survival after standard treatment. SYSUCC-001 study presented in ASCO 2020 reported an increased disease-free survival after one year of metronomic capecitabine in operable TNBC patients after completion of local therapy. As per our clinical experience in metastatic breast cancer, many Indian patients are not able to tolerate capecitabine for longer duration. Hence, we wanted to assess the tolerance and safety of one year of daily dosing of capecitabine in our patients with Non-Metastatic TNBC. Methods: We performed a retrospective analysis of non-metastatic TNBC patients receiving adjuvant capecitabine 650 mg /m2 twice daily continuously for one year who took treatment from June 2020 to August 2022. The data extracted included patient socio-demographics, capecitabine information, side effects, and capecitabine treatment changes (dose reductions and dose interruptions). Statistical analysis was conducted using SPSS, version 24. Results: We analyzed 90 patients, out of which majority (62%) were stage II. Median age of the cohort was 48 years. Germline data was available for 64 patients, out which 8 patients were BRCA 1 positive and 8 patients had a variant of undetermined significance. Median duration of capecitabine in our patients was 230 days (IQR: 10 - 360). Twenty-six (28.8%) patients underwent dose reduction and 15 (16.6%) had reported grade 3 toxicity. Mean dose of capecitabine received was 535 mg / m2 twice daily. Treatment was interrupted due to toxicity in 20 (22%) of patients. The most common capecitabine-induced toxicity was hand foot syndrome, which was also the most common reason for dose reduction and treatment interruption. Dihydropyrimidine dehydrogenase (DPD) mutation status was known for 38 patients out of which only one (2.6%) was found to have DPD deficiency. Incidence of grade 3 toxicity was observed to be less in patients with age less than 50 years, ECOG performance status 0-1 and absence of comorbidities. Two-year disease free survival (DFS) and overall survival (OS) was estimated to be 79.3% and 80% respectively. Most common site of metastases was reported to be brain followed by lung. Conclusions: Continuous metronomic dosing of adjuvant capecitabine for 1 year is fairly well tolerated in Indian patients with non-metastatic TNBC, but may still require dose reduction in some patients due to toxicity.

Clinical utility of ctDNA as a tool to detect triple-negative breast cancer relapses: The CUPCAKE trial.

TPS1139 Background: The current follow-up of triple-negative breast cancer (TNBC) patients at high risk of relapse does not involve any blood or imaging monitoring to detect metastases, because of the low sensitivity and specificity of blood and imaging biomarkers in that context. In contrast, ctDNA detection techniques are highly specific, sensitive and can detect a molecular relapse several months before the occurrence of symptoms (1). We hypothesize that the early detection of molecular relapse by ctDNA combined with whole-body mapping of tumor recurrence sites by 68Ga-FAPI-46-PET/CT will enable the detection of relapses when they are still limited in size and number of sites. Detecting oligometastatic relapses could demonstrate a clinical utility by (i) allowing the use of local treatments in addition to systemic treatments; (ii) taking advantage of the higher efficacy of immunotherapy in patients with limited tumor burden and inflammation. Methods: CUPCAKE is a randomized, non-comparative, multicenter trial promoted by Institut Curie (Paris, France), which design is inspired from the Trials WIthin CohortS approach (2). N=450 non-metastatic TNBC patients at high risk of relapse will be included after having signed a written informed consent in a cohort allowing them to be followed by ctDNA monitoring. For each included patient, a ctDNA detection assay (FoundationOne Tracker) will be performed every 3 months, with a turnaround time of less than 3 weeks. When negative, ctDNA detection results will not be disclosed to patients nor clinicians. If, at any timepoint, ctDNA is detected (molecular relapse), patients will be randomized in a 1:1 ratio between the experimental arm (ctDNA-based intervention) and the control arm (no intervention). In the experimental arm, the positive ctDNA result will be disclosed. To locate metastatic foci, patients will be offered to undergo whole-body imaging with 18F-FDG and 68Ga-FAPI-46-PET/CT, in addition to any other workup considered as relevant by their treating physician. If/when a clinical/radiological relapse is observed, systemic or local treatments will be decided by physicians (standard of care). In the control arm, patients and their treating physician will not be made aware of the molecular relapse and will continue the standard surveillance with repeated ctDNA test every 3 months (blinded). At the time of the clinical/radiological diagnosis of relapse, similar procedures will be performed (18F-FDG &amp; 68Ga-FAPI-46-PET/CT). The primary endpoint is overall survival rate at 24 months after the randomization in the experimental arm while the control arm will serve as reference. Secondary endpoints include efficacy criteria like progression-free survival but also clinical features upon radiological/radiological relapse, or performance criteria of 68Ga-FAPI-46 versus 18F-FDG PET/CT. 1. Coombes, Clin Cancer Res. 2019. 2. Relton, BMJ. 2010. Clinical trial information: 06225505.

Abstract PS14-07: Exploring Circulating Leukocyte RNA Expression: Implications for Treatment Outcomes and Immune-Related Adverse Events in Patients with Triple Negative Breast Cancer Enrolled in the GeparNuevo Trial

Abstract Abstract Exploring Circulating Leukocyte RNA Expression: Implications for Treatment Outcomes and Immune-Related Adverse Events in Patients with Triple Negative Breast Cancer Enrolled in the GeparNuevo Trial Background: Significant research has been conducted on the influence of immune checkpoint inhibitor therapy on tumor microenvironment, particularly with regard to tumor-infiltrating immune cells. Nevertheless, our understanding of the circulating immune repertoire and its association with treatment outcomes remains limited. Consequently, our subproject of the GeparNuevo trial aimed to explore the RNA phenotype of circulating leukocytes and its impact on overall survival (OS), and adverse events of patients enrolled in the GeparNuevo trial (Loibl S et al. Annals Oncol 2022). Methods: The GeparNuevo phase II trial focused on the effects of neoadjuvant nab-paclitaxel followed by epirubicin/cyclophosphamide (nabP-EC) chemotherapy combined with the anti-PD-L1 immune checkpoint inhibitor durvalumab versus placebo in patients with non-metastatic triple-negative breast cancer. RNA-stabilizing PAXgene tubes were used to collect blood samples prior to treatment initiation. RNA was extracted from circulating leukocytes of 117 patients and analyzed using a custom NanoString nCounter CodeSet, including 290 immune-related target genes. The associations between 16 immune cell scores, 26 immune signaling scores, 31 individual gene expression patterns, OS, and immune-related adverse events (irAEs) were analyzed. Results: Univariate Cox regression analysis using continuous scores revealed a significant correlation between PIP3 activates AKT signaling, T cells, CDK2, and TIMP1 expression with OS in the placebo arm. Higher expression of PIP3 activates AKT signaling, T cells, and CDK2, as well as lower expression of TIMP1, were associated with prolonged survival. Notably, T cell scores and CDK2 expression exhibited a significant interaction with the treatment arm (p=0.0489 and 0.0210, respectively). Multivariate Cox regression analysis demonstrated a significant association of DPP4, ICOS and MYC expression with OS. Additionally, CDK2, CDKN2A, F5 and HLA-DRA expression were linked to the presence of irAEs. In the durvalumab arm, TNFR2 non canonical NFkB pathway signaling, CDK2 and CDKN2A expression showed an inverse association with the occurrence of irAEs. Conclusions: Our study provides preliminary evidence that RNA derived from circulating leukocytes may serve as a potential biomarker for predicting treatment outcomes and identifying patients prone to develop side effects during standard-of-care chemotherapy or immune checkpoint therapy. These findings highlight the potential utility of peripheral immune cell RNA profiling in improving treatment strategies and patient management. Further research and validation are necessary to fully comprehend the clinical significance and broader implications of these findings. Citation Format: Hanna Hübner, Matthias Ruebner, Andreas Schneeweiss, Carsten Denkert, Hans-Peter Sinn, Michael Braun, Thomas Karn, Bruno V. Sinn, Dirk-Michael Zahm, Jörg Thomalla, Jens Huober, Claus Hanusch, Michael Untch, Christine Solbach, Theresa Link, Natalie Filmann, Julia Rey, Johannes Holtschmidt, Sibylle Loibl, Peter A. Fasching. Exploring Circulating Leukocyte RNA Expression: Implications for Treatment Outcomes and Immune-Related Adverse Events in Patients with Triple Negative Breast Cancer Enrolled in the GeparNuevo 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 PS14-07.

Abstract PO4-03-05: Prognostic value of Ki67 expression in post-treatment tumors of patients with residual triple-negative breast cancer after neoadjuvant chemotherapy

Abstract Introduction Patients with triple-negative breast cancer (TNBC) who do not achieve pathological complete response (pCR) against neoadjuvant chemotherapy (NAC) have a poor prognosis. The prognosis of these patients can be differentiated using various parameters, including the Residual Cancer Burden (RCB) index and tumor-infiltrating lymphocytes. In this study, we took a different angle and aimed to evaluate the prognostic value of post-treatment Ki67 expression, which was examined in tumors following NAC in patients with non-pCR TNBC. Methods A retrospective review of clinical records from February 2008 to December 2021 was conducted of patients from Gangnam Severance Hospital and Asan Medical Center, both in Seoul, South Korea. We included patients with non-metastatic TNBC who underwent NAC including anthracycline and taxane regimens, followed by curative surgery, regardless of adjuvant capecitabine receipt. Ki67 expression and the RCB index were evaluated using residual tumors obtained from surgery. High Ki67 expression was defined as ≥20%. The 5-year recurrence-free survival (RFS) was estimated using Kaplan-Meier analysis, and hazard ratios (HR) were calculated using Cox regression analysis. Results This study included 338 patients with available Ki67 expression data in residual tumors. Among them, 110 patients (30.9%) had low Ki67 expression, while 228 patients (64%) had high Ki67 expression. At a median follow-up of 34 months, those with low Ki67 expression had a 5-year RFS rate of 82.6%, while those with high Ki67 expression had a rate of 58.3%, with a HR of 0.345 (95% CI 0.210-0.565, p&amp;lt; 0.001). When stratified by the RCB index, the 5-year RFS of RCB-I patients was 93%, RCB-II patients 70.2%, and RCB-III patients 40.5%. When assessing survival outcomes based on both Ki67 expression and the RCB index, patients with RCB-I and low Ki67 (n=26) had a 100% 5-year RFS rate. Patients with RCB-I and high Ki67 (n=24) had a rate of 83.3%. Notably, in patients with RCB-III and high Ki67 (n=62), the 5-year RFS rate was 35.5% and there was no significant difference in RFS based on the receipt of adjuvant capecitabine (median RFS: capecitabine - 18 months, observation - 15 months, p-value=0.994). Conclusions Our findings demonstrate the prognostic value of Ki67 expression in residual TNBC after NAC, indicating that cases with low Ki67 expression have a favorable outcome. Combining Ki67 expression with the RCB index allows identification of patients with good residual disease (i.e. low Ki67 expression and RCB-I) who could be potential candidates for de-escalating adjuvant treatments such as capecitabine or pembrolizumab. However, for patients with high Ki67 expression and RCB-III, novel strategies are required to improve survival outcomes beyond the use of capecitabine. Citation Format: Yoonwon Kook, Soo-Young Lee, Seung Ho Baek, Min Ji Kim, Junghyun Kim, Sohyun Moon, Seung Eun Lee, Soong June Bae, Joon Jeong, Sae Byul Lee, Sung Gwe Ahn. Prognostic value of Ki67 expression in post-treatment tumors of patients with residual triple-negative breast cancer after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-03-05.

Abstract PO1-03-05: Tolerance of adjuvant radiotherapy combined with pembrolizumab for triple negative breast cancer

Abstract BACKGROUND AND PURPOSE: The current standard-of-care management of locally advanced triple negative breast cancer (TNBC) is based on neoadjuvant chemo-immunotherapy with pembrolizumab, surgery, radiotherapy and adjuvant pembrolizumab. However, the safety of combining pembrolizumab with adjuvant breast radiotherapy has never been evaluated. This study evaluated the tolerance profile of concurrent pembrolizumab (P) with adjuvant radiotherapy (RT) in locally advanced TNBC patients. METHODS: This bicentric ambispective study included the first prospectively registered patients with non-metastatic TNBC treated with the KEYNOTE-522 regimen in our institution. They received P in combination with carboplatin and paclitaxel chemotherapy and a second chemotherapy with doxorubicin and cyclophosphamide, followed by surgery and locoregional RT with or without P as adjuvant treatment. RT was normo- or hypofractionated, for the breast or chest wall, with or without lymph node irradiation according to institutional guidelines. Adjuvant P was administered at a total dose of 1800 mg at 200 mg once every 3 weeks or 400 mg once every 6 weeks. The safety profile was evaluated during and after the end of RT (until the last contact) with CTCAE V.5 scale. RESULTS: A total of 55 patients (pts) were prospectively included between July 2021 and March 2023. The median age was 49 years (29-69). The median follow-up was 12 months ( range, 10-26). Of them, 27 (49%) did not receive P concomitantly with RT (RT-only group) because of neo-adjuvant treatment related toxicities, and 28 (51%) received P concomitantly with RT (P-RT group). There was no statistical difference in population and toxicity between the RT-only group and the P-RT group. Nine patients were diagnosed with cardiac toxicities before the beginning of the RT and did not receive P during the RT. No RT-induced grade ≥4 toxicities were observed. Early toxicities were mainly grade 1-2. Two grade 3 toxicities occurred (1 case of axillary pain in the P-RT group and 1 radiodermatitis in the RT-only group). No cardiac or pulmonary toxicities ≥grade 2 were observed with adjuvant therapy. The toxicity profile is given in table 1. DISCUSSION: In these series, the main cause of discontinuation of pembrolizumab was related to suspicion of cardiac adverse events occurring during the neoadjuvant treatment and related to the injection of pembrolizumab or of the chemotherapy. All myocarditis happened before radiotherapy and did not affect the administration of radiotherapy. In this context, the optimal radiotherapy technique and cardiac dose constraints after ICI-induced myocarditis is unknown and late cardiotoxicity studies will be needed to precise these points. Cardiac sparing techniques, such as deep-inspiration breath hold, proton therapy, or alternative positioning (such as isocentric lateral decubitus) could be considered. CONCLUSION: Adjuvant radiotherapy can be combined with pembrolizumab for TNBC patients without increasing the risk of radiation-induced adverse events, allowing maintaining a systemic treatment in these high-risk patients. Longer follow-up and prospective studies are needed to validate these results. Adjuvant treatment-related adverse events Citation Format: Youlia Kirova, Thaïs Tison, Pierre Loap, Emilie ARNAUD, Kim Cao, Solène Bringer, Manon Kissel, Safia Maaradji, Juliette Mainguene, Jean-Yves Pierga, Florence Lerebours, Anne Salomon, Mariana Mirabelle, Delphine Loirat, Francois-Clement Bidard. Tolerance of adjuvant radiotherapy combined with pembrolizumab for 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 PO1-03-05.

Abstract PS16-06: Tumor-infiltrating lymphocytes and pathologic response to neoadjuvant chemotherapy with the addition of platinum and pembrolizumab in TNBC: A single-center real-world study

Abstract Background Previous studies have presented compelling evidence suggesting that the inclusion of platinum agents alongside anthracyclines and taxanes could potentially enhance treatment outcomes in high-risk triple-negative breast cancer (TNBC). Moreover, pembrolizumab has been integrated into clinical practice as a part of standard-of-care for non-metastatic TNBC with high risk. In light of these findings, we undertook a real-world study to investigate the impact of incorporating platinum agents and pembrolizumab on achieving pathologic complete response (pCR) in TNBC patients undergoing neoadjuvant chemotherapy (NAC). Furthermore, we specifically examined the influence of tumor-infiltrating lymphocytes (TILs) on the treatment outcomes. Patients and Methods In this real-world study conducted at Gangnam Severance Hospital, Seoul, Republic of Korea, we analyzed a cohort of 398 patients with TNBC who underwent surgery following NAC between March 2007 and November 2022. Among them, 247 patients received an anthracycline-taxanes (A-T), 120 received a carboplatin regimen including A-T, and 31 received a pembrolizumab regimen including A-T-carboplatin as part of their neoadjuvant chemotherapy treatment. TIL was evaluated in biopsied samples prior to NAC according to the guideline of TIL international working group. The high TIL was defined with a cutoff of 50%. Results Among the 398 patients analyzed, 87 (21.9%) had high TIL tumors. The pCR rates were 32% in the anthracycline-taxane (A-T) regimen group, 57% in the A-T-carboplatin regimen group, and 68% in the pembrolizumab with A-T-carboplatin regimen group. Within the high TIL group, the pCR rate did not increase with the addition of carboplatin (51.8% in the A-T group and 41.7% in the A-T-carboplatin group), but reached 85.7% with the addition of pembrolizumab and carboplatin. Among the low TIL group, the pCR rate increased from 26.7% to 61.1% with the addition of carboplatin, but there was no difference in the pCR rate between the carboplatin and pembrolizumab groups (61.1% and 60.9%, respectively). In clinically node-positive patients, the pCR rate significantly increased with pembrolizumab in the high TIL group (40.9% versus 100%, p=0.035). However, in low TIL patients, the addition of carboplatin alone significantly increased the pCR rate to 62.3%, whereas the addition of pembrolizumab did not show the same effect. Conclusions Our real-world data consistently demonstrates an increased pCR rate with the addition of carboplatin and pembrolizumab. Among patients with high TIL, the addition of carboplatin did not result in an elevated pCR rate. However, the addition of pembrolizumab tended to maximize the pCR rate, surpassing 80%. On the other hand, among patients with low TIL, the addition of carboplatin significantly increased the pCR rate, while the addition of pembrolizumab did not have the same effect. Efforts should be made to improve the response to pembrolizumab-containing regimens for patients with low baseline TIL levels. Citation Format: Min Ji Kim, Yoonwon Kook, Seung Ho Baek, Junghyun Kim, Sohyun Moon, Seung Eun Lee, Jee Hung Kim, Soong June Bae, Sung Gwe Ahn, Joon Jeong. Tumor-infiltrating lymphocytes and pathologic response to neoadjuvant chemotherapy with the addition of platinum and pembrolizumab in TNBC: A single-center real-world study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS16-06.

Abstract 1173: T cell receptor diversity in buffy coat samples from subsets of breast and ovarian cancer patients

Abstract Background: Immunotherapy, mainly by the use of immune checkpoint inhibitors (ICI), has been established as a standard option for both, solid tumors and hematological malignancies. Unfortunately, this success has only been replicated in a subset of patients (pts) with gynecological cancers. In ovarian cancer (OC), response rates to ICI monotherapy were low and in breast cancer (BC), only the subgroup of triple-negative BC (TNBC) pts showed an improved outcome by the addition of ICI. One reason for limited success of immunotherapy might be an impaired immune system. In this regard, monitoring the T cell receptor (TCR) repertoire could provide key insights into adaptive immune responses to ultimately understand disease initiation, progression and treatment response. Here we elucidated TCR alpha, beta, gamma and delta in buffy coats of pts with non-metastatic OC as well as non-metastatic and metastatic TNBC and compared the results with healthy donors (HDs). Methods: RNA was isolated from buffy coat samples of 20 HDs, 10 treatment-naïve primary OC pts, 14 treatment-naïve, non-metastatic TNBC pts (participating in the phase II neomono trial) and 19 pts with metastatic TNBC by a modified QIAamp RNA Blood Mini protocol. A survey of the TCR diversity and mapping of common and unique TCRs was done using the QIAseq Targeted RNA Panel Human TCR panel for all known T-cell receptors (alpha, beta, gamma, delta). Results: Regardless of the cancer entity, a significant reduction in TCR diversity was observed compared to HDs with the greatest differences observed in the delta receptors. When OC samples were compared with HDs, the difference in diversity was highly significant for all TCR subtypes (TCRalpha: p=0.013; TCRbeta: p=0.008; TCRgamma: 0.008; TCRdelta: 0.006). Similar results were obtained for non-metastatic TNBC (TCRalpha: p=0.0002; TCRbeta: p=0.0001; TCRgamma: p=0.002; TCRdelta: p=0.002) as well as metastatic TNBC patients (TCRalpha: p=0.001; TCRbeta: p=0.001; TCRgamma: p=0.005; TCRdelta: p=0.003) when their TCR diversity was compared to HDs. Interestingly, no significant differences in diversity were obtained when treatment-naïve non-metastatic TNBC pts were compared with heavily pretreated metastatic TNBC pts. The lowest diversity was found in BC pts compared to the OC pts. Conclusion: We have initiated a survey of the TCR diversity in TNBC and OC patients. Further evaluations will include the correlation of these findings with clinical characteristics and outcome. Whether the reduced TCR diversity represents T cell exhaustion or T cell specialization cannot yet be deduced from the results. Nevertheless, the addition of a TCR diversity score could provide an additional metric which may help provide patient guidance when integrated into a multi-modal molecular test. Citation Format: Corinna Keup, Cornelia Kolberg-Liedtke, Song Tian, Samuel J. Rulli, Siegfried Hauch, Paul Buderath, Oliver Hoffmann, Rainer Kimmig, Sabine Kasimir-Bauer. T cell receptor diversity in buffy coat samples from subsets of breast and ovarian cancer patients [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 1173.

Different Chemotherapy Regimens and Pathologic Complete Response in Triple-Negative Breast Cancer: An Updated Network Meta-Analysis of Phase 3 Trials.

Background and Objectives: Currently, the standard treatment for non-metastatic triple-negative breast cancer (TNBC) consists of a systemic neoadjuvant (or perioperative) anthracycline plus taxane-based chemotherapy, delivered either sequentially or concomitantly. We performed a network meta-analysis (NMA) to compare the relative efficacy of different neoadjuvant treatments for TNBC in terms of pathologic complete response (pCR). Materials and Methods: The MEDLINE, Embase, and Cochrane databases were searched from database inception to 1 November 2023. Randomized clinical trials were used that enrolled adults with stage I-III TNBC and provided data on pCR defined as residual ypT0/TisN0M0. Between-group comparisons were estimated using risk ratios (RRs) with 95% credible intervals (95% CrIs). The primary outcome was the pCR rate. Results: 1129 citations were screened, and 12 randomized clinical trials were included. In Bayesian comparisons, all regimens, except anthracycline/taxanes plus gemcitabine or capecitabine, resulted in a higher pCR than the standard regimen in both direct and indirect comparisons. In particular, immunotherapy-based regimens resulted in more than double the pCR compared to historical regimens (RR = 2.3, 95% CI 1.9-2.9) and ranked as being the optimal regimen with a probability of 97%. Disease-free survival was better for immune checkpoint inhibitor-based chemotherapy (HR = 0.36, 95% 1.21-2.09) than for historical regimens. Conclusion: This meta-analysis confirmed that incorporating immunotherapy with neoadjuvant platinum-based chemotherapy is the best option to guarantee remarkable pathologic downstaging and improve clinical outcomes.

Pathologic and immunohistochemical prognostic markers in residual triple-negative breast cancer after neoadjuvant chemotherapy.

The persistence of residual tumour after neoadjuvant chemotherapy (NAC) in localised triple-negative breast cancer (TNBC) is known to have a negative prognostic value. However, different degrees of expression of some immunohistochemical markers may correlate with different prognoses. The expression of biomarkers with a known prognostic value, i.e., cytokeratin 5/6 (CK5/6), androgen receptor (AR), epidermal growth factor receptor (EGFR) proliferation-related nuclear antigen Ki-67, human epidermal growth factor receptor 2 (HER2), protein 53 (p53), forkhead box protein 3 (FOXP3), and cluster differentiation 8 (CD8), was analysed by immunohistochemistry in 111 samples after NAC in non-metastatic TNBC patients addressed to Georges-François Leclerc Cancer Centre Dijon, France. Clinical and pathological variables were retrospectively collected. Cox regression was used to identify immunohistochemical (IHC) and clinicopathological predictors of event-free survival (EFS) (relapse or death). Median age was 50.4 years (range 25.6-88.3), 55.9% (n = 62) were non-menopausal, 70 (63.1%) had stage IIA-IIB disease. NAC was mostly sequential anthracycline-taxanes (72.1%), and surgical intervention was principally conservative (51.3%). We found 65.7% ypT1, 47.2% lymph node involvement (ypN+), and 29.4% lymphovascular invasion (LVI). Most residual tumours were EGFR >110 (H-score) (60.5%, n = 66), AR ≥4% (53.2%, n = 58), p53-positive mutated (52.7%, n = 58), CD8 ≥26 (58.1%, n = 61), FOXP3 ≥7 (51.4%, n = 54), more than half in the stroma, and 52.3% (n = 58) HER2 score 0. After a median follow-up of 80.8 months, 48.6% had relapsed. Median EFS was 62.3 months (95% CI, 37.2-not reached (NR)). Factors independently associated with poor EFS were AR-low (p = 0.002), ypN+ (p < 0.001), and LVI (p = 0.001). Factors associated with lower overall survival (OS) were EGFR-low (p = 0.041), Ki-67 high (p = 0.024), and ypN+ (p < 0.001). Post-NAC residual disease in TNBC showed biomarkers specific to a basal-like subtype and markers of lymphocyte infiltration mostly present in the stroma. Prognostic markers for EFS were AR, LVI, and ypN and warrant further validation in a prognostic model.

Assessment of novel prognostic biomarkers to predict pathological complete response in patients with non-metastatic triple-negative breast cancer using a window of opportunity design.

Triple-negative breast cancer (TNBC) includes approximately 20% of all breast cancer and is characterized by its aggressive nature, high recurrence rates, and visceral metastasis. Pathological complete response (pCR) is an established surrogate endpoint for survival. The window of opportunity studies provide valuable information on the disease biology prior to definitive treatment. To study the association of dynamic change in pathological, imagining, and genomic biomarkers that can prognosticate pCR. The study aims to develop a composite prognostic score. Clinical, interventional, and prognostic biomarker study using the novel window of opportunity design. The study aims to enroll 80 treatment-naïve, pathologically confirmed TNBC patients, administering a single dose of paclitaxel and carboplatin during the window period before neoadjuvant chemotherapy (NACT). Tumor tissue will be obtained through a tru-cut biopsy, and positron emission tomography and computed tomography scans will be performed for each patient at two time points aiming to evaluate biomarker alterations. This will be followed by the administration of standard dose-dense NACT containing anthracyclines and taxanes, with the study culminating in surgery to assess pCR. The study would develop a composite prognostic risk score derived from the dynamic change in the Ki-67, tumor-infiltrating lymphocytes, Standardized Uptake Value (SUV max), Standardized Uptake Value for lean body mass (SUL max), and gene expression level pre- and post-intervention during the window period prior to the start of definitive treatment. This outcome will aid in categorizing the disease biology into risk categories. The current study is approved by the Institutional Ethics Committee [Ethics: Protocol. no. JIP/IEC/2020/019]. This study was registered with ClinicalTrials.gov [CTRI Registration: CTRI/2022/06/043109]. The validated biomarker score will help to personalize NACT protocols in patients in TNBC planned for definitive treatment.

Axillary Nodal Metastases Conversion and Perioperative Complications with Neoadjuvant Pembrolizumab Therapy in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is known to portend a worse prognosis compared with same-stage, hormone receptor-positive disease. However, with the recent change in practice to include pembrolizumab in neoadjuvant chemotherapy (NAC) for TNBC, an increase in pathologic complete responses (pCRs) has been reported. The perioperative repercussions of adding pembrolizumab to standard NAC regimens for TNBC are currently unknown. We aimed to explore the perioperative implications of adding pembrolizumab to standard NAC regimens for non-metastatic TNBC. This was a retrospective review of the perioperative outcomes in patients with non-metastatic TNBC treated with pembrolizumab-NAC from January 2018 to October 2022 conducted at a high-volume cancer center. Patient demographics, comorbidities, clinical and pathological staging, NAC treatment regimen, initiation, and completion, as well as date of surgery and postoperative complications were analyzed. Of 87 patients, 67.8% had an overall pCR and 86% had an axillary pCR; 37.2% of cN+ patients were spared from axillary lymph node dissection. However, 24.1% of patients experienced surgical complications, 9% of patients were receiving steroids at the time of breast surgery secondary to adverse effects of pembrolizumab-NAC, and 7% underwent a change in the initial surgical plan such as omission of reconstruction. Pembrolizumab-NAC has not only significant oncologic benefit but also noteworthy perioperative implications in the surgical management of TNBC.

Outcomes of Metaplastic Breast Cancer Versus Triple-Negative Breast Cancer: A Propensity Score Matching Analysis.

This study aims to compare the survival outcomes of metaplastic breast cancer (MPBC) with triple-negative breast cancer (TNBC) and identify prognostic factors that influence the survival outcomes of MPBC patients and TNBC patients. Patients with nonmetastatic MPBC or TNBC were reviewed from our database. Patients' clinicopathologic and molecular features were analyzed with respect to outcomes, including disease-free survival (DFS) and overall survival (OS). Propensity score matching (PSM) with a one-to-three matching between MPBC patients and TNBC patients was performed. A total of 857 female patients (76 MPBC patients and 781 TNBC patients) were included in this study. A subgroup of triple-negative MPBC (n = 60) was matched with TNBC (n = 180) cases based on patient characteristics and treatments. Kaplan-Meier analysis indicated that the MPBC group was associated with worse OS and DFS before (P = 0.0046 both) and after (P = 0.011 and P = 0.0046, respectively) PSM. Multivariable analysis revealed that a higher T stage (T > 2) (P = 0.032) and higher lymph node stage (N3 vs. N0-2, P = 0.012) were associated with worse OS after PSM. For DFS, the MPBC group (P = 0.012), higher T stage (T > 2) (P = 0.032), and higher lymph node stage (N3 vs. N0-2, P = 0.045) were associated with worse DFS. Among the 76 MPBC patients, a higher T stage and mesenchymal differentiation were associated with worse OS (pT1/2 vs. pT3/4 and mesenchymal differentiation vs. other subtypes, P = 0.007 and P = 0.011, respectively). Compared with TNBC, MPBC was associated with worse OS and DFS. Mesenchymal differentiation has a worse DFS than other subtypes of MPBC.

RNA expression levels from peripheral immune cells, a minimally invasive liquid biopsy source to predict response to therapy, survival and immune-related adverse events in patients with triple negative breast cancer enrolled in the GeparNuevo trial.

1011 Background: The impact of immune checkpoint therapy on the tumor microenvironment including tumor-infiltrating immune cells is well described. However, little is known about the circulating immune repertoire and its association with treatment outcome. Hence, we set out to investigate the RNA phenotype of peripheral immune cells before and during treatment of patients enrolled in the GeparNuevo trial (Loibl S et al. Annals Oncol 2022). Methods: The GeparNuevo trial investigated the outcome after neoadjuvant nabP-EC-chemotherapy in combination with the anti-PD-L1 immune checkpoint inhibitor durvalumab versus placebo in patients with non-metastatic triple negative breast cancer. Blood was collected before therapy (baseline), after window, before epirubicin/cyclophosphamide and at end of treatment. RNA from circulating leucocytes of 117 patients was extracted and analyzed using a custom NanoString nCounter CodeSet. Expression of 290 immune-related genes was quantified. The association of RNA expression and signatures with outcome parameters like pathologic complete response (pCR), distant disease-free survival (DDFS), invasive disease-free survival (iDFS), overall survival (OS), and immune-related adverse events (irAEs) were investigated. Results: Immune cell type scores representing macrophages and neutrophils significantly increased during treatment, while B cell, T and Th1 cell scores decreased (p &lt; 0.0001, respectively) regardless of treatment arm. Multivariate logistic respectively multivariate Cox regression analysis revealed a significant association of each baseline DPP4 and MYC gene expression with pCR, DDFS, iDFS, and OS in patients. CDK2, F5 and HLA-DR mRNA expressions were associated with the presence of irAEs. The signature score for TNFR2 non-canonical NF-kB pathway, which is known for its protective capacity, was inversely associated with irAEs in the durvalumab arm (OR = 0.454, 95% CI 0.231-0.892, p = 0.0220). Multiple immune-related signatures at baseline were associated with tumor mutational burden. Conclusions: Our study indicates the importance of the peripheral immune phenotype for treatment response and survival. This association between RNA expression levels of circulating immune cells and outcome seems to be not only relevant for patients receiving immune checkpoint therapy, but also for those under standard chemotherapy alone. Clinical trial information: NCT02685059 .

The prognostic value of tumour-infiltrating lymphocytes, programmed cell death protein-1 and programmed cell death ligand-1 in Stage I-III triple-negative breast cancer.

Tumour-infiltrating lymphocytes (TILs) represent a robust biological prognostic biomarker in triple-negative breast cancer (TNBC); however, the contribution of different subsets of immune cells is unclear. We investigated the prognostic value of immune markers, including stromal TILs (sTILs), CD8+T and FOPX3+T cells, PD-1 and PD-L1 in non-metastatic TNBC. In total, 259 patients with Stage I-III TNBC were reviewed. The density of sTILs along with the presence of total (t), stromal (s), and intratumoral (i) CD8+T cells and FOPX3+T cells were evaluated by haematoxylin and eosin and immunohistochemical staining. Immunohistochemical staining of PD-1, PD-L1 was also conducted. All immune markers were positively correlated with each other (P < 0.05). In the multivariate analysis, sTILs (P = 0.046), tCD8+T cells (P = 0.024), iCD8+T cells (P = 0.050) and PD-1 (P = 0.039) were identified as independent prognostic factors for disease-free survival (DFS). Further analysis showed that tCD8+T cells (P = 0.026), iCD8+T cells (P = 0.017) and PD-1 (P = 0.037) increased the prognostic value for DFS beyond that of the classic clinicopathological factors and sTILs. In addition to sTILs, inclusion of tCD8+T, iCD8+T cells, or PD-1 may further refine the prognostic model for non-metastatic TNBC beyond that including classical factors alone.

The Association between Early-Onset Diagnosis and Clinical Outcomes in Triple-Negative Breast Cancer: A Systematic Review and Meta-Analysis

Early-onset diagnosis, defined by age <40 years, has historically been associated with inferior outcomes in breast cancer. Recent evidence suggests that this association is modified by molecular subtype. We performed a systematic review and meta-analysis of the literature to synthesize evidence on the association between early-onset diagnosis and clinical outcomes in triple-negative breast cancer (TNBC). Studies comparing the risk of clinical outcomes in non-metastatic TNBC between early-onset patients and later-onset patients (≥40 years) were queried in Medline and EMBASE from inception to February 2023. Separate meta-analyses were performed for breast cancer specific survival (BCSS), overall survival (OS), and disease-free survival (DFS), locoregional recurrence-free survival (LRRFS), distant recurrence-free survival (DRFS), and pathological complete response (pCR). In total, 7581 unique records were identified, and 36 studies satisfied inclusion criteria. The pooled risk of any recurrence was significantly greater in early-onset patients compared to later-onset patients. Better BCSS and OS were observed in early-onset patients relative to later-onset patients aged >60 years. The pooled odds of achieving pCR were significantly higher in early-onset patients. Future studies should evaluate the role of locoregional management of TNBC and the implementation of novel therapies such as PARP inhibitors in real-world settings, and whether they improve outcomes.

Abstract P4-03-06: Clinical and socioeconomic disparities in treatment and survival between Hispanic and non-Hispanic Black women with non-metastatic Triple-Negative Breast Cancer

Abstract Background: Breast cancer(BC) is a common female malignancy [1]. Triple-negative breast cancer (TNBC) is the least common (10-15% of cases)[2], but the most aggressive subtype. TNBC accounts for 5% of all-cancer-related deaths every year[3, 4].Hispanic women are 1.3 more likely to develop TNBC [3, 5]. Whether Hispanic and non-Hispanic patients suffering from TNBC show different survival. We aim: (1) to evaluate the differences in overall (OS) and breast cancer specific survival(BCSS) between Hispanic(H) and non-Hispanic black (NHB) women in non-metastatic TNBC, and (2) to assess the contribution of sociodemographic, clinical, and neighborhood factors to TNBC survival disparities. Methods: With the SEER database of the National Cancer Institute, we identified 4271 (39%) H and 6594 (61%) NHB patients who were diagnosed with non-metastatic TNBC between 2010 and 2016. Patients with tumor in situ were excluded from the analysis. Logistic regression was used to identify odd ratios for treatment modalities. Kaplan-Meir methods were used to estimate OS and BCSS. Competing risk analysis was used to asses the association between race/ethnicity and risk of breast cancer mortality adjusting for age, insurance, social, SDI, rurality, BC stage, tumor grade, surgery, chemotherapy, and radiation therapy. Results: The mean age at diagnosis for H vs. NHB was 53 and 56 years, respectively (p &amp;lt; 0.001). 54% of Hispanics were married vs. 35 % of NHB, p &amp;lt; 0.001. Tumor size &amp;gt; 5 cm was present in 14% NHB vs. 12% H patients, p &amp;lt; 0.001. Grade I tumors were only 1 % in both groups, grade II were 13% and grade III-IV were 82% also in both groups, p &amp;gt;0.99. H (28% stage I, 50% stage II) had more advance disease as compared to NHB (30% stage I, 48% stage II) [p &amp;lt; 0.001]. Private insurance was more common in NHB than H (74% vs. 66%, p &amp;lt; 0.001). Rural residence was more common in NHB than H (8% vs. 3 %, p&amp;lt; 0.001). High level of SDI was more common in H as compared to NHB(43% vs. 36%, p &amp;lt; 0.001). Surgery was performed in 92% of NHB and 91% of H, p = 0.03. Radiation was given to 54% of NHB and 43% of H, p &amp;lt; 0.001, while chemotherapy was given to 79% of NHB and 79% of H patients, p = 0.54. After adjusting for clinicopathological features, the odds ratio (ORs) for receiving surgery, radiation, and chemotherapy for NHB as compared to H were 0.9 (p = 0.32), 1.57 (p &amp;lt; 0.001), and 0.89 (p = 0.03), respectively. The 5-year OS and BCSS rates were higher in H as compared to NHB(OS 76% vs. 72%, p &amp;lt; 0.001; BCSS 81% vs. 78%, p &amp;lt; 0.001). For stage I patients, neither 5-year OS (86% vs. 89%, p= 0.054) nor BCSS (91% vs. 93%, p= 0.37) was different between NHB and H patients. For stage II and III patients, the 5-year OS rates for Hispanics vs. NHB were (79% vs 74%, p &amp;lt; 0.001) and (51% vs 45%, p &amp;lt; 0.004), respectively. After adjusting for age, marital status, insurance, stage, grade, treatment, SDI, rurality; NHB have higher risk of BC death as compared to H patients (subdistribution Hazard Ratio (HR) = 1.39; 95% CI 1.2 – 1.56, p &amp;lt; 0.001). The association between race/ethnicity and risk of breast cancer death was not affected by age (p=0.44), insurance(p=0.89), SDI(p=0.40), or living in a rural area(p=0.14). The risk of BC death between NHB and H was even higher for patients who did not receive radiation (HR 1.5) than in those who received radiation (HR 1.2). The risk of BC death between NHB and H was also higher for patients who did not undergo surgery (HR 1.7) than in those who underwent surgery (HR 1.3). Conclusions: In patients with non-metastatic TNBC, H patients present with increased rates of high-grade and advanced stage tumors than NHB. NHB are 57% more likely to receive radiation and 11% less likely to receive chemotherapy than H women. NHB patients have a 39% higher risk of BC death as compared to H even after adjusting for clinicopathological, treatment and socioeconomic factors. Future studies need to assess potential etiologies for racial disparities in BC outcomes such as differences in tumor microenvironment, access to healthcare, tumor biology and treatment efficacy. Citation Format: Alvaro Alvarez Soto, Ana Maria Bernal, Jesus Anampa Mesias. Clinical and socioeconomic disparities in treatment and survival between Hispanic and non-Hispanic Black women with non-metastatic Triple-Negative Breast Cancer [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 P4-03-06.

Abstract P2-11-17: Prognostic value of Trop2 expression levels in non-metastatic triple-negative breast cancer and correlation with other biomarkers

Abstract Background: Since the development of anti Trop2 antibody-drug conjugates (ADC), Trop2 has been validated as a major therapeutic target for antibody-drug conjugates in metastatic triple-negative breast cancer (TNBC). However, very few data have been reported regarding the prognostic implication, or clinicopathological variables, associated with Trop2 expression levels in early TNBC. Our aim was to evaluate Trop2 expression and its prognostic value in a retrospective series of patients with non-metastatic TNBC and a long follow-up, characterized for Basal-like (BL) or molecular apocrine-like (MA) IHC profiles as well as TILs infiltrate, PDL1 expression and PIK3CA/PTEN mutations. Patients and methods: The analysis was performed in a series of 228 patients with non-metastatic TNBC treated in our center between 2002 and 2012 arrayed on 6 TMA. BL and MA profiles were defined as IHC CK5/6 and/or EGFR expression, and Androgen-receptor and FOXA1 IHC expression, respectively. Trop2 expression levels were tested for their association with baseline clinicopathological variables, and for Relapse-Free Survival (RFS) and Overall survival (OS). Trop2 IHC level of expression was evaluated using the ENZ-ABS380 mouse monoclonal antibody and the methodology described by Bardia et al. (Annals of Oncology, 2021) to quantify the membrane signal. First, we established a score grid, according to staining intensity (no labeling: 0; weak labeling: 1; moderate labeling: 2; strong labeling: 3). Then, for each sampled core, the percentage of labeled invasive tumor cells in each intensity was reported. The overall membrane expression was then calculated using the H-Score method (3 x % of cells with labeling intensity 3 + 2 x % of cells with intensity 2 + 1 x % of cells with intensity 1). The scores obtained ranged from 0 to 300. Results: Median age was 58.2 years (range 28.5-89.1). 43.9% of tumors were classified pT1 and 63.5% pN0. 83.8% of patients had ductal carcinomas. Histological grade 1-2 represented 22.7% of all tumors. A BL phenotype was observed in 68.1% of cases, and an MA profile in 39.4% of the cases. Adjuvant chemotherapy (ACT) was delivered in 74% of patients. We observed low Trop2 expression (H-Score &amp;lt; 100) in 12.3% of the cases (28/228 samples), moderate Trop2 expression (H-Score 100-200) in 28.9% of the cases (66/228 samples), and strong Trop2 expression (H-Score &amp;gt;200) in 58.8% of the cases (134/228 samples). We only identified 3 tumors without any Trop2 expression. Regarding baseline clinicopathological correlations, Trop2 levels were only found significantly associated with pT stage, pT1 tumors displaying more frequently high Trop2 scores compared to tumors &amp;gt;= pT2 (p=0.002). No significant correlation was found between Trop2 expression levels and HER2 levels (0 vs. 1+/2+), BL or MA status. With a median follow-up of 9.7 years, Trop2 levels were not associated with RFS nor OS in univariate analysis. In multivariate analysis, poor RFS was associated with classical variables in the early TNBC setting: tumors &amp;gt;=T2 stage (Hazard Ratio (HR) 2.13, p=0.02), N+ status (HR 3.51, p&amp;lt; 0.001), while high (&amp;gt;5%) TILs infiltration levels (HR 0.54, p=0.03) and adjuvant chemotherapy use (HR 0.49, p=0.007) were associated with improved RFS. Conclusions: Trop2 is expressed in nearly all early TNBC cases, and Trop2 levels of expression, while associated with T stage, did not impact survival in this population. These results are consistent with the ones reported in the metastatic setting in the ASCENT trial. Trop2 level of expression appearing homogeneous distributed in all the clinicopathological subtypes of TNBC, advocating for the evaluation of combined treatments with anti-Trop2 ADCs and dedicated targeted therapies in specific TNBC subgroups. Citation Format: William Jacot, Marie-Christine Chateau, Simon Thezenas, Séverine Guiu, Nelly Firmin, Florence Boissière-Michot. Prognostic value of Trop2 expression levels in non-metastatic triple-negative breast cancer and correlation with other biomarkers [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 P2-11-17.

Abstract P1-13-12: Targeting Dynamin-related protein 1 for the management of taxane-resistant triple-negative breast cancer

Abstract The development of drug resistance is a primary cause of chemotherapy failure in the treatment of triple-negative breast cancer (TNBC). Some cancer cells are resistant to drugs with unrelated structures and mechanisms of action, a phenomenon known as multidrug resistance (MDR). Although taxanes such as docetaxel and paclitaxel are effective against non-metastatic and metastatic TNBC and other types of breast cancer, they eventually become ineffective due to development of drug resistance. Mitochondrial dynamics has gained significant attention as a means to treat MDR and non-MDR cancers. Mitochondrial dynamics determine the number, shape, and location of mitochondria within cells, which are fundamental to the health of the cell. Among its key components is the mitochondrial fission-promoting dynamin-related protein 1 (Drp1). There is mounting evidence indicating that both Drp1 and its phosphorylated form promote cancer survival, resistance to apoptosis, and chemoresistance. We observed increased phosphorylation of Drp1 at Ser616 as well as phosphorylation of its upstream kinase ERK1/2 in TNBC lines SUM159PT and its paclitaxel-resistant derivative that we developed called SUM159PT/PAC200 that displays more than an 80-fold increase in resistance to paclitaxel. Using CRISPR-Cas9 technology, we knocked out the gene encoding Drp1 in both lines. When Drp1 is genetically ablated, paclitaxel resistance in SUM159PT/PAC200 was significantly reversed. Furthermore, proliferation, migration, and invasion capabilities were decreased in both parental and paclitaxel-resistant Drp1 knockout lines. In SUM159PT/PAC200 Drp1-KO cells, a mesenchymal to epithelial transition (MET) was observed as indicated by downregulation of mesenchymal markers such as N-cadherin and -catenin, and upregulation of the epithelial marker ZO-1. Interestingly, Drp1 knockout halted the ability of SUM159PT/PAC200 to form colonies in soft agar. SUM159PT/PAC200 cells strongly express the MDR pump P-glycoprotein (ABCB1), to which paclitaxel is a known substrate, and genetically targeting Drp1 reduced the expression to almost undetectable levels. Taken together, these findings suggest that Drp1 is both a resistance factor and a key protein in breast cancer proliferation and dissemination, making it a promising actionable molecular target in the treatment of TNBC. Further studies are in progress to understand the role of Drp1 in the development and maintenance of MDR phenotype, proliferation, and invasion. Citation Format: David Terrero, Amit Tiwari, Dayanidhi Raman. Targeting Dynamin-related protein 1 for the management of taxane-resistant triple-negative breast cancer [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 P1-13-12.

Abstract P2-21-06: The relationship between the gene expression difference of fibroblasts in the tumor microenvironment and metastasis of triple-negative breast cancer

Abstract Background Triple negative breast cancer (TNBC) is a breast cancer subtype with increased risk of distant metastasis, especially to lung and liver. In addition to the intrinsic characteristics of tumor cells, the molecular features of the tumor microenvironment cells can also regulate the metastasis process of TNBC. In this study, we tried to characterize the transcriptomic features of microenvironment fibroblasts associated with the distant metastasis of TNBC. Method We established PDX models by obtaining tumor tissues from 26 triple-negative breast cancer patients and transplanting them into the mammary fat pads of immunodeficient mice. When the PDX tumors grew sufficiently in the fat pads, we excised them and saved the mice to assess whether each PDX tumor was capable of developing spontaneous distant metastasis. We used bulk RNA sequencing and single cell RNA sequencing to determine the transcriptomic features associated with the distant metastasis. Results We classified the 26 TNBC PDX models based on their in vivo metastasis capacity and the clinical outcomes of the corresponding patients. Non-metastatic PDX models were defined as the lack of developing distant metastasis in either mouse experiment or clinical follow-up data (n=5). PDX models were defined as metastatic models when they developed distant metastasis in both mouse and human (n=4). We performed single cell RNA sequencing using the nine PDX tumors and observed a substantial gene expression differences of fibroblasts in the tumor microenvironment between the metastatic and non-metastatic PDX models. The fibroblasts of the metastatic PDX models showed up-regulation of genes involved in the response to hypoxia, inflammatory response, neutrophil chemotaxis, cellular response to IL-1, positive regulation of cell proliferation, and negative regulation of apoptotic process. Moreover, this difference of gene expression between metastatic and non-metastatic TNBC PDX models were not identified by the bulk RNA sequencing data. Conclusion By using the single cell RNA sequencing using the TNBC PDX models, we identified key features of fibroblasts in the tumor microenvironment that contributes to the metastasis capacity of TNBC. Further studies are on-going to elucidate the underlying mechanisms. Citation Format: Woo Hang Heo, Woochan Lee, SONGBIN LI, Jong-Il Kim, Hyeong-Gon Moon. The relationship between the gene expression difference of fibroblasts in the tumor microenvironment and metastasis of triple-negative breast cancer [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 P2-21-06.