Cancer Subtypes Research Articles

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

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

T-reg transcriptomic signatures identify response to check-point inhibitors

Regulatory T cells (Tregs) is a subtype of CD4+ T cells that produce an inhibitory action against effector cells. In the present work we interrogated genomic datasets to explore the transcriptomic profile of breast tumors with high expression of Tregs. Only 0.5% of the total transcriptome correlated with the presence of Tregs and only four transcripts, BIRC6, MAP3K2, USP4 and SMG1, were commonly shared among the different breast cancer subtypes. The combination of these genes predicted favorable outcome, and better prognosis in patients treated with checkpoint inhibitors. Twelve up-regulated genes coded for proteins expressed at the cell membrane that included functions related to neutrophil activation and regulation of macrophages. A positive association between MSR1 and CD80 with macrophages in basal-like tumors and between OLR1, ABCA1, ITGAV, CLEC5A and CD80 and macrophages in HER2 positive tumors was observed. Expression of some of the identified genes correlated with favorable outcome and response to checkpoint inhibitors: MSR1, CD80, OLR1, ABCA1, TMEM245, and ATP13A3 predicted outcome to anti PD(L)1 therapies, and MSR1, CD80, OLR1, ANO6, ABCA1, TMEM245, and ATP13A3 to anti CTLA4 therapies, including a subgroup of melanoma treated patients. In this article we provide evidence of genes strongly associated with the presence of Tregs that modulates the response to check point inhibitors.

Androgen receptor: Structure, signaling, function and potential drug discovery biomarker in different breast cancer subtypes.

The Androgen Receptor (AR) is emerging as an important factor in the pathogenesis of breast cancer (BC), which is the most common malignancy worldwide. >70 % of AR expression in primary and metastatic breast tumors has been observed which suggests that AR may be a new marker and a potential therapeutic target among AR-positive BC patients. Biological insight into AR-positive breast cancer reveals that AR may cross-talk with several vital signaling pathways, including key molecules and receptors. Downstream signaling of AR might also affect many clinically important pathways that are emerging as clinical targets in BC. AR exhibits different behaviors depending on the breast cancer molecular subtype. Preliminary clinical research using AR-targeted drugs, which have already been FDA-approved for prostate cancer (PC), has given promising results for AR-positive breast cancer patients. However, since AR positivity's prognostic and predictive value remains uncertain, it is difficult to identify and stratify patients who would benefit from AR-targeted therapies alone. Thus, the need of the hour is to target the androgen receptor as a monotherapy or in combination with other conventional therapies which has proven to be an effective clinical strategy for the treatment of prostate cancer patients, and these therapeutic strategies are increasingly being investigated in breast cancer. Therefore, in this manuscript, we review the role of AR in various cellular processes that promote tumorigenesis and aggressiveness, in different subtypes of breast cancer, as well as discuss ongoing efforts to target AR for the more effective treatment and prevention of breast cancer.

The discerning influence of dynamic contrast-enhanced MRI in anticipating molecular subtypes of breast cancer through the artistry of artificial intelligence - a narrative review.

Radio genomics is an exciting new area that uses diagnostic imaging to discover genetic features of diseases. In this review, we carefully examined existing literature to evaluate the role of artificial intelligence (AI) and machine learning (ML) on dynamic contrastenhanced MRI (DCE-MRI) data to distinguish molecular subtypes of breast cancer (BC). Implications to noninvasive assessment of molecular subtype include reduction in procedure risks, tailored treatment approaches, ability to examine entire lesion, follow-up of tumour biology in response to treatment and evaluation of treatment resistance and failure secondary to tumour heterogeneity. Recent studies leverage radiomics and AI on DCE-MRI data for reliable, non-invasive breast cancer subtype classification. This review recognizes the potential of AI to predict the molecular subtypes of breast cancer non-invasively.

Narrow interval dual phase 18F-FDG PET/CT: A practical approach for distinguishing tumor recurrence from radiation necrosis in brain metastasis.

Purpose of our research is to demonstrate efficacy of narrow interval dual phase [18F]-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) imaging in distinguishing tumor recurrence (TR) from radiation necrosis (RN) in patients treated for brain metastases. 35 consecutive patients (22 female, 13 male) with various cancer subtypes, lesion size > 1.0 cm3, and suspected recurrence on brain magnetic resonance imaging (MRI) underwent narrow interval dual phase FDG-PET/CT (30 and 90 min after tracer injection). Clinical outcome was determined via sequential MRIs or pathology reports. Maximum standard uptake value (SUVmax) of lesion (L), gray matter (GM), and white matter (WM) was measured on early (1) and delayed (2) imaging. Analyzed variables include % change, late phase, and early phase for L uptake, L/GM uptake, and L/WM uptake. Statistical analysis (P < .01), receiver operator characteristic (ROC) curve and area under curve (AUC) cutoff values were obtained. Change in L/GM ratio of > -2% was 95% sensitive, 91% specific, and 93% accurate (P < .001, AUC = 0.99) in distinguishing TR from RN. Change in SUVmax of lesion alone was the second-best indicator (P < .001, AUC = 0.94) with an ROC cutoff > 30.5% yielding 86% sensitivity, 83% specificity, and 84% accuracy. Other variables (L alone or L/GM ratios in early or late phase, all L/WM ratios) were significantly less accurate. Utilizing narrow interval dual phase FDG-PET/CT in patients with brain metastasis treated with radiation therapy provides a practical approach to distinguish TR from RN. Narrow time interval allows for better patient comfort, greater efficiency of PET/CT scanner, and lower disruption of workflow.

Focal adhesion kinase-YAP signaling axis drives drug-tolerant persister cells and residual disease in lung cancer

Targeted therapy is effective in many tumor types including lung cancer, the leading cause of cancer mortality. Paradigm defining examples are targeted therapies directed against non-small cell lung cancer (NSCLC) subtypes with oncogenic alterations in EGFR, ALK and KRAS. The success of targeted therapy is limited by drug-tolerant persister cells (DTPs) which withstand and adapt to treatment and comprise the residual disease state that is typical during treatment with clinical targeted therapies. Here, we integrate studies in patient-derived and immunocompetent lung cancer models and clinical specimens obtained from patients on targeted therapy to uncover a focal adhesion kinase (FAK)-YAP signaling axis that promotes residual disease during oncogenic EGFR-, ALK-, and KRAS-targeted therapies. FAK-YAP signaling inhibition combined with the primary targeted therapy suppressed residual drug-tolerant cells and enhanced tumor responses. This study unveils a FAK-YAP signaling module that promotes residual disease in lung cancer and mechanism-based therapeutic strategies to improve tumor response.

Exploring the epigenetic profile of ID4 in breast cancer: bioinformatic insights into methylation patterns and chromatin accessibility dynamics.

Inhibitor of differentiation 4 (ID4) is a dominant-negative regulator of basic helix-loop-helix (bHLH) transcription factors. The expression of ID4 is dysregulated in various breast cancer subtypes, indicating a potential role for ID4 in subtype-specific breast cancer development. This study aims to elucidate the epigenetic regulation of ID4 within breast cancer subtypes, with a particular focus on DNA methylation and chromatin accessibility. Bioinformatic analyses were conducted to assess DNA methylation and chromatin accessibility in ID4 regulatory regions across breast cancer subtypes. Gene Set Enrichment Analysis (GSEA) was conducted to identify related gene sets. Transcription factor binding within ID4 enhancer and promoter regions was explored. In vitro experiments involved ER+ breast cancer cell lines treated with estradiol (E2) and Tamoxifen. Distinct epigenetic profiles of ID4 were observed, revealing increased methylation and reduced chromatin accessibility in luminal subtypes compared to the basal subtype. Gene Set Enrichment Analysis (GSEA) implicated estrogen-related pathways, suggesting a potential link between estrogen signaling and the regulation of ID4 expression. Transcription factor analysis identified ER and FOXA1 as regulators of ID4 enhancer regions. In vitro experiments confirmed the role of ER, demonstrating reduced ID4 expression and increased methylation with estradiol treatment. Conversely, Tamoxifen treatment increased ID4 expression, indicating the potential involvement of ER signaling through ERα in the epigenetic regulation of ID4 in breast cancer cells. This study shows the intricate epigenetic regulation of ID4 in breast cancer, highlighting subtype-specific differences in DNA methylation and chromatin accessibility.

Abstract PO2-17-02: Can body mass index be a complete pathological response predictor in breast cancer patients submitted to neoadjuvant chemotherapy? A real-world data trial

Abstract Background: Breast cancer is a prevalent disease, and Its incidence has increased annually worldwide. The prognosis depends on several factors, such as patient characteristics, tumor characteristics and treatment efficacy. In this scenario, neoadjuvant chemotherapy (NAC), previously used only to make surgical approach possible in advanced cases, has been increasingly used in more aggressive initial tumors such as HER 2 positive and triple negative and, in these tumors, the presence of pathological complete response is directly correlated with survival and the disease-free interval. Obesity is very common in Brazil and in the world, and its incidence grows annually. There is a direct relationship between the risk of breast cancer and obesity, especially in postmenopausal women. Justification: Many authors suggest that obese patients are less likely to achieve this pathological complete response (pCR). Real-world data is important to evaluate how patients behave in the real world, only 5% of the patients are enrolled in clinical trials. Most of the clinical trials have strict inclusion and exclusion criteria that ends up selecting a patient that almost doesn't exist in the real world. Objective: To correlate complete pathological response with Body Mass Index (BMI) and, secondarily, to evaluate the relationship between overall and disease-free survival with BMI. Methods: This was a retrospective observational study that has evaluated patients with invasive breast cancer in two Brazilian hospitals. Clinical and pathological characteristics were extracted from the database, being eligible the patients diagnosed with invasive breast cancer, stages I to III, and who underwent neoadjuvant chemotherapy (NAC). Patients were categorized using the World Health Organization (WHO) definition: BMI 18.5 to &amp;lt; 25 kg/m2: normal weight; BMI 25 to &amp;lt; 30 kg/m2: overweight; BMI ≥30kg/m2: obesity. pCR was defined as the absence of breast and axillary invasive tumor. The t test or chi-square test were used to individually analyze the association of each variable between the groups with and without RPc. Univariate and multivariate analyzes to calculate odds ratios (OR) and 95% confidence intervals (CI) of the independent variables BMI, age, clinical stage, histological type, and subtype of cancer, correlated with pCR. where p value &amp;lt; 0.05 was considered statistically significant. Results: 1,779 records were included in the analyses, with a mean age of 50 years at diagnosis and a mean BMI of 28.08 kg/m2. Most patients had stage III cancer (68.1%) at diagnosis and the invasive carcinoma nonspecial type was predominant (95.2%). Immunohistochemistry allowed us to divide the groups into Luminal A like (12.4%), Luminal B like (31.1%), HER2+ like (25.3%) and triple negative like (31.2%). After NAC, 1461 had residual disease and 390 (22.3%) had a pCR. Regarding stages, 2% of the patients were in stage I, 30% in stage II and 68% in stage III. No correlation was found between BMI categories and pCR (p=0.7607). In the multivariate analysis, the results were also not significant for the correlation between the BMI categories after adjusting for age, clinical stage, tumor histology and subtype of breast cancer. We observed, however, that the most aggressive types of cancer were predictors of pathologic complete response. The estimated average overall survival (OS) was 102 months for those of normal weight, 99 months for the overweight ones and 101 months for the obese ones. As for recurrence-free survival, the data were immature. Conclusion: This study with Brazilian real-world data found no correlation between BMI and pCR after NAC and BMI and OS in patients with breast cancer. As an additional finding, most patients were obese or overweight at diagnosis (69%) and public policies should be encouraged to act in this scenario. Trials considering stratification of patients between different regions of the country or specific subtype of cancer can elucidate this finding. Citation Format: Fernanda Grace Bauk Richter, Andre Mattar, Marcelo Antonini, Juliana Real, Luis Henrique Gebrim, Reginaldo Coelho Lopes. Can body mass index be a complete pathological response predictor in breast cancer patients submitted to neoadjuvant chemotherapy? A real-world data 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 PO2-17-02.

Abstract PO4-21-01: Recurrent Desmoid Tumor and Ductal Carcinoma In Situ in an African-American Woman: A Case Report and Discussion on Disparities for These Two Cancer Subtypes

Abstract Introduction: Disparities in cancer care in patients from different races and ethnicities unfortunately do exist and are well described in literature. Hormonal-driven cancers, such as some soft-tissue tumors and DCIS, have been demonstrated to impact African-American women (AAW) disproportionately. These patients are at increased risk for not only development of these cancers, but also experience disparities in survival, treatment outcomes, and modalities of treatment. Clinical Case: A 47-year-old premenopausal AAW with past medical history of recurrent desmoid sarcoma of the abdomen and ductal carcinoma in-situ (DCIS) of the left breast presented to oncology clinic with recurrent abdominal mass. The patient was originally diagnosed with DCIS in the left breast in 2018 and subsequently underwent left breast mastectomy with TRAM reconstruction and fat graft later that year. In 2020, the patient noticed a left lower abdominal growth that quickly enlarged and became painful. She underwent imaging without biopsy and was taken to surgery in April 2021 with tumor removal and mesh placement. Pathology showed desmoid fibromatosis infiltrating skeletal muscle and involving the inked resection margin of the specimen. Conservative re-excision and additional therapy was recommended but not done at the time. In 2022, the patient had resection of the area again with pathology of the incisional scar showing skin and deep soft tissue foci suspicious for recurrent desmoid fibromatosis extending to the inked deep margin. No mesh was placed, and the wound closed almost completely. The patient was not aware of positive margins at the time. In January 2023, patient again notice a new bump that was bothersome. Initial CT and MRI without finding of defined mass, but with right rectus thickening and enlarged right external iliac lymph node. Core biopsy in June 2023 confirmed recurrent desmoid fibromatosis. In April 2023, annual screening with mammogram was performed with a finding of 2.9 cm cluster of heterogenous calcification in the right breast. Diagnostic mammogram and ultrasound performed. Core needle biopsy was subsequently performed in May with pathology consistent with high grade DCIS with low ER and PR positivity. Lymph node biopsy was negative, but clinically positive. She is currently undergoing further genetic testing with surgical workup for mastectomy. Discussion and Conclusion: AAW diagnosed with DCIS have higher all-cause and disease specific mortality in comparison to white women (WW) diagnosed with DCIS. AAW are also at increased risk of aggressive secondary breast cancers in both the ipsilateral and contralateral breast in comparison to other races. In regards to tumor biology, WW have been shown to have higher ER and PR positivity in both primary and primary breast cancers than AAW. In many of these large-scale studies higher mortality, recurrence, and metastasis in AAW have been identified regardless of treatment modality. Research into differences in treatment between AAW and WW has shown that AAW, in contrast to our patient case, are more likely to undergo endocrine and radiation therapy rather than mastectomy. Although there does not seem to be an increased risk of desmoid fibromatosis in AAW when compared to WW, other soft-tissue tumors and malignancies do show a predilection for AAW. Incidence of sarcoma in black patients is higher than white patients, and black patients also have poorer survival outcomes. This case provides an example of the intersectionality of two cancer subtypes that impact black patients disproportionately. More evidence is required to unearth the reasons why these two cancer subtypes which are driven by similar processes impact AAW to a greater degree. Citation Format: Vinita Akula, Jessica Jones. Recurrent Desmoid Tumor and Ductal Carcinoma In Situ in an African-American Woman: A Case Report and Discussion on Disparities for These Two Cancer Subtypes [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 PO4-21-01.

Abstract PO3-08-05: Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes

Abstract Background: Special histologic subtypes of breast cancer, including mucinous and tubular, account for 25% of all invasive breast cancers. Multigene tests (MGT) play a crucial role in guiding adjuvant chemotherapy and predicting prognosis for the patients with Hormone receptor-positive HER2-negative breast cancer. This research aims to examine the results of multigene tests for special histologic subtype patients and review the prognosis of each group. Methods: A retrospective analysis was conducted on data from 133 patients with special histologic subtypes of breast cancer who underwent surgery at Severance Hospital between November 2013 and December 2022. Each patient underwent one type of MGT, including Oncotype Dx, MammaPrint, or EndoPredict. Patients were grouped in two groups according to histologic types, based on WHO classification. Favorable types consist of type A mucinous carcinoma, pure tubular carcinoma, invasive solid papillary carcinoma, encapsulated papillary carcinoma with invasion, invasive cribriform carcinoma, secretory carcinoma, and invasive carcinoma with apocrine differentiation. Unfavorable types included type B mucinous carcinoma, mucinous carcinoma with micropapillary feature or neuroendocrine differentiation, mixed IDC, ILC or invasive micropapillary carcinoma, mixed invasive solid papillary carcinoma, mixed invasive papillary carcinoma, and mixed invasive cribriform carcinoma with IDC. Results: Patients with favorable types accounted for 42.86% (57 patients), while patients with unfavorable types accounted for 57.14% (76 patients). Patients with unfavorable histologic subtypes of breast cancer tended to have a higher incidence of high-risk results in MGT, as well as a greater prevalence of multiple (multifocal, multicentric) cancer and higher histologic grade. In multivariate analysis using logistic regression, unfavorable types showed a significantly high ratio of having high risk on MGT compared to the favorable type (OR = 4.327, 95% CI 1.210 – 15.475, p-value = 0.024). Moreover, overall survival in unfavorable histologic types showed a statistically significant difference between high-risk and low-risk in Kaplan-Meier survival analysis (p-value = 0.001). Conclusions: Unfavorable subtypes have shown a significantly higher-risk result of MGT, and patients with unfavorable types of breast cancer and high-risk MGT results have exhibited the worst prognosis. Consequently, we can suggest that MGT can be used as a prognosis evaluation tool for certain special subtypes of breast cancer and further utilized to aid in treatment decisions. Citation Format: Seung Hye Yang, Jee Hyun Ahn, Suk Jun Lee, Jee Ye Kim, Hyung Seok Park, Seung Il Kim, Byeong Woo Park, Seho Park. Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-08-05.

Abstract PS04-06: Breast cancer recurrence among women with pre-diagnostic major depression and co-existing substance abuse disorder: A retrospective study in the United States Veterans Health Administration Cohort

Abstract Background: Our prior study observed a 34% higher risk of breast cancer (BC) recurrence among women with major depressive disorder (MDD) at the time of their BC diagnosis compared to women without MDD after adjusting for sociodemographic, clinical, and prognostic factors. Given the high prevalence of substance abuse disorders among individuals with MDD and the positive association between alcohol use and mortality among BC survivors, we were interested to examine whether the risk of BC recurrence was compounded for women with both conditions. Objective: To investigate whether pre-diagnostic substance abuse disorders modify the association between MDD and BC recurrence. Methods: We established a retrospective cohort of women (age ≥ 18 years) with incident, early-stage BC diagnosed from 2010 through 2019 using the VHA’s electronic medical record database. A two-year window was used to identify women with MDD and co-existing substance abuse disorders prior to their BC diagnosis. We examined potential interactions between MDD and alcohol abuse and MDD and other substance abuse using multivariable proportional hazards regression, accounting for competing risk of death. Our outcome of interest was BC recurrence. The reference group for all analyses was women with BC alone. The models were adjusted for patient characteristics including age, race, ethnicity, marital status, rurality of primary residence, priority group rating (proxy for socioeconomic status), any homelessness or economic problems, comorbidity burden, body mass index, smoking status, receipt of a screening mammography, year of BC diagnosis, cancer stage, cancer subtype, and cancer treatment. Subgroup analyses were conducted by cancer subtype. Results: Our cohort comprised 6,045 women with BC, of whom 1,754 (29%) had a pre-diagnostic MDD diagnosis and 1,509 (25%) had a substance abuse disorder. Among women with MDD, 386 (22%) abused alcohol and 336 (19%) abused other substances. The median length of follow-up from BC diagnosis was 4.5 years (IQR=4.8 years). The average age at BC diagnosis was 57 years (SD=11 years) overall, 56 years (SD=10 years) among women with MDD, and 57 years (SD=9 years) among women with substance abuse disorders. On multivariable analysis, MDD (HR=1.33; 95% CI: 1.14, 1.53), alcohol abuse disorder (HR=1.37; 95% CI: 1.12, 1.68), and other substance abuse disorders (HR=1.33; 95% CI: 1.13, 1.56) were independent risk factors for BC recurrence. Further, there was a statistically significant interaction between pre-diagnostic MDD and alcohol abuse disorder (p-interaction=0.003). Women with BC who had both pre-diagnostic MDD and alcohol abuse disorder were at a 65% (HR=1.65; 95% CI: 1.29, 2.11) higher risk of BC recurrence compared to women with BC alone. A statistically significant interaction was also observed between pre-diagnostic MDD and other substance abuse disorders (p-interaction &amp;lt; 0.001). Women with BC who had both pre-diagnostic MDD and other substance abuse disorders were at a 90% (HR=1.90; 95% CI: 1.50, 2.42) higher risk of BC recurrence compared to women with BC alone. In subgroup analyses, the interaction between MDD and alcohol abuse disorders (p-interaction=0.001) and MDD and other substance abuse disorders (p-interaction &amp;lt; 0.001) was limited to women with estrogen receptor positive cancer but not estrogen receptor negative cancer. Conclusion: Women with incident BC who have prior diagnoses of both MDD and substance abuse disorder are at higher risk of recurrence than women with either exposure independently. Further research is needed to examine the etiology of our findings and to evaluate whether this newly defined risk group would benefit from closer monitoring and more tailored treatment options. Citation Format: Maya Aboumrad, Kala Visvanathan. Breast cancer recurrence among women with pre-diagnostic major depression and co-existing substance abuse disorder: A retrospective study in the United States Veterans Health Administration Cohort [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS04-06.

Abstract PO1-27-07: Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative

Abstract Background: Overexpression of HER2 is a significant prognostic and predictive factor in early breast cancer. HER2 positive tumors are those scored by immunohistochemistry (IHC) 3+ or 2+ with amplification by in situ hybridization (ISH). These tumors may benefit from HER2-targeted treatment and additionally, in early HER2-positive BC, achieving a complete pathological response after neoadjuvant treatment improves patient survival. In recent years, new anti-HER2 antibody-drug conjugates have proven effective for HER2 low BC (defined as IHC score 1+ or 2+ not amplified) in the metastatic disease setting; however, in HER2-low early BC, studies testing novel anti-HER2 antibody-drug conjugates as neoadjuvant therapy (NAT) are ongoing. Currently, we don´t know exactly whether HER2 expression can influence the pathological response rate after NAT or disease-free survival (DFS) in these patients compared to HER2-zero (IHC 0). The aim of our study is to determine the impact on response rate to NAT and survival outcomes in early HER2-negative BC. Methods: We conducted a retrospective study in two hospitals in Andalucia, Spain. Patients with early HER2 negative BC treated with NAT from January 2015 to June 2022 were included. Patients were divided into HER2 low patients (IHC 1+ or 2+ not amplified) and HER2 0 (IHC 0). We collected clinical and pathological characteristics, pathological response rate using the Residual Cancer Burden (RCB) system where a complete pathological response (pCR) was defined as ypT0/ypTis and ypN0, and survival outcomes. The primary objective of the study was to analyze the pCR rate after NAT according to HER2 score, and secondary objectives were to assess disease-free survival and overall survival (DFS and OS rates). Results: 574 patients were included (100% women). 397 patients had hormone receptors (luminal BC) on these tumors, and 177 did not have them, i.e., triple-negative BC (TNBC). 225 patients were HER2-zero, and 312 patients were HER2-low (253/312 patients had luminal BC and 59/312 patients were TNBC). The pCR in HER2-low patients was 17.3% and 23.1% in HER2-zero patients (p=0.047). For luminal BC patients, the pCR was 16.7% in HER2-low tumors and 13.7% in HER2-zero tumors (p=0.29). Similarly, there was no difference in pCR rates in TNBC patients (45.8% in HER2-low and 53.8% in HER2-zero tumors, respectively, (p=0.958). The overall survival (OS) at 96 months was 88.7% (95% CI 85.6%-92%). Regarding survival outcomes, neither HER2 expression level was associated with higher 8-year DFS: 81.1% in HER2-low patients (95% CI 75.7%-86.8%) and 74.9% in HER2-zero patients (95% CI 62.3%-90.1%) p=0.64. There was no difference between histological subtypes at 8-years regarding DFS rate: 80.5% (95% CI 74.3%-87.2%) in luminal HER2-low patients and 76.3% (95% CI 60.8%-95.7%) in luminal HER2-zero patients, p=0.22; 83.8% in TNBC HER2-low (95% CI 74.5%-94.2%) and 77.5% in TNBC HER2-zero patients (95% CI 69.4%-86.6%) p=0.26. We also didn´t find significant differences in terms of OS. For HER2-low patients, the 8-year OS was 90.9% (95% CI 87%-94.9%) and for HER2-zero patients, it was 86.4% (95% CI 80.8%- 92.5%) p=0.46. There were also no differences in OS for different histological subgroups with an 8-year OS in luminal HER2-low breast cancer patients of 92.5% (95% CI 88%-96.7%) and 87% in HER2-zero (95% CI 78.9%-96.1%) p=0.91. In patients with triple-negative breast cancer phenotype, the OS was 84.2% for HER2-low (95% CI 74.5%-95.2%) and 85.3% for HER2-zero (95% CI 77.9%-93.4%) p=1. Conclusions: We found no difference in survival outcomes and response rate to conventional NAT between HER2-low and HER2-zero expression levels. Therefore, our data do not support the hypothesis of HER2-low as a biologically specific breast cancer subtype. Further research on this approach with HER2 antibody-drug conjugate schemes as an alternative to traditional NAT schemes is warranted. Citation Format: Ana Gil-Torralvo, Yeray Rodriguez, Alejandro Falcon, David Morales, Mónica Cejuela, Isabel Miras, Marta Amérigo, Manuel Ruíz - Borrego, Juan Bayo, Francisco Javier Salvador Bofill. Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative [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 PO1-27-07.

Abstract PO5-02-09: Discordance of the PAM50 intrinsic subtypes with the immunohistochemistry-based subtypes in HER2-negative early breast cancer treated with neoadjuvant chemotherapy

Abstract Background The PAM50 (Prosigna Breast Cancer Gene Signature Assay) can be used to assess the expression levels of 50 genes in early breast cancer biopsies, including formalin-fixed paraffin-embedded (FFPE) tissue from human epidermal growth factor receptor 2 (HER2)-negative patients. However, there is currently no practical molecular assay for intrinsic subtype in real-world practice that addresses the problems of cost and run-time. Methods In the phase 2 HER2E-PAM/PAMILIA study (NCT04817540), we prospectively analyzed molecular subtyping through the PAM50 test in low HER2 (HER2 IHC 1+ or 2+ SISH-) breast cancer patients. PAM50 intrinsic subtypes were determined according to 50 cancer genes using the NanoString nCounter Analysis System. This study was originally designed to determine whether adding HER2-targeted treatment in HER2 enriched molecular subtype increases the pathologic complete rate (pCR). We aimed to analyze the discordance between immunohistochemistry (IHC)-based surrogate subtyping of pre- &amp; post-operative tissues and PAM50 intrinsic subtypes, and to assess the pCR according to the discordance. Results In a total 82 patients, the proportions of HR+/HER2- and triple negative breast cancer (TNBC) in the preoperative tissue were 85.4% (n=70) and 14.6% (n=12), respectively. According to PAM50 intrinsic subtypes, 11.0% (n=9) were basal, 8.5% (n=7) were HER2-enriched, 34.1% (n=28) were luminal A, 36.6% (n=30) were luminal B, and 3.7% (n=3) were normal-like type. In total, 32 patients (41.5%) were discordant between IHC-based preoperative subtype and PAM50 intrinsic subtype. Among the 70 patients with HR+/HER2-, non-luminal A, B type was found in 12.9% with basal-like, 8.6% with HER2-enriched, and 4.3% with normal-like type, respectively. Of 12 TNBC patients, 83.3% were luminal A, B type, and 8.3% were HER2-enriched. In the other hands, 6 patients (13.0%) were discordant between IHC-based post-operative subtype and PAM50 intrinsic subtype. Among the 40 patients with HR+/HER2- postoperative subtype, non-luminal A, B type was found in 2.5% with basal-like, 2.5% with HER2-enriched, and 5.0% with normal-like type, respectively. Of 6 TNBC postoperative patients, 16.7% were normal-like. Most received anthracycline- and taxane-based neoadjuvant chemotherapy. During data analysis (June 2023), 54 cases underwent surgery after neoadjuvant chemotherapy. 4 of 54 patients (7.4%) achieved a pCR, of which one was HER2-enriched, one was luminal B-like, and two were basal-like PAM50 intrinsic subtype. However, discordance of IHC based subtype with intrinsic subtype was not considerable and was not correlated with pCR. Conclusion A substantial portion of patients showed discrepancy between preoperative and postoperative IHC subtype and PAM50 intrinsic subtype in our study. Citation Format: Jee Hung Kim, Soong June Bae, Sung Gwe Ahn, Jeonghee Lim, Min Hwan Kim, Gun Min Kim, Joo Hyuk Sohn, Joon Jeong. Discordance of the PAM50 intrinsic subtypes with the immunohistochemistry-based subtypes in HER2-negative early breast cancer treated with 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 PO5-02-09.

Abstract PO2-08-02: Evaluation of predictive and prognostic value of androgen receptorexpression in breast cancer subtypes treated with neoadjuvantchemotherapy

Abstract Background Neoadjuvant chemotherapy is the standard treatment for local advanced breast cancer administered to shrink tumors and destroy undetected metastatic cells, thereby facilitating subsequent surgery. Previous studies have shown that AR may be used as a prognostic predictor in breast cancers, but its role in neoadjuvant therapy and the relationship with prognosis of different molecular subtypes of breast cancer need to be further explored. Methods We retrospectively evaluated 1231 breast cancer patients with complete medical records at Tianjin Medical University Cancer Institute and Hospital who were treated with neoadjuvant chemotherapy between January 2018 to December 2021. All the patients were selected for prognostic analysis. The follow-up time ranged from 12 to 60 months. We first analyzed the AR expression in different subtypes of breast cancer and its correlation with clinicopathological features. Meanwhile, the association of AR expression and pCR of different breast cancer subtypes was investigated. Finally, the effect of AR status on the prognosis of different subtypes of breast cancer after neoadjuvant therapy was analyzed. Results The positive rates of AR expression in HR +/HER2-, HR +/HER2 +, HR-/HER2 + and TNBC subtypes were 82.5%, 86.9%, 72.2% and 34.6%, respectively. Histological grade III (P = 0.014, OR = 1.862, 95% CI 1.137 to 2.562), ER positive expression (P = 0.002, OR = 0.381, 95% CI 0.102 to 0.754) and HER2 positive expression (P = 0.006, OR = 0.542, 95% CI 0.227 to 0.836) were independent related factors for AR positive expression. AR expression status was associated with pCR rate after neoadjuvant therapy only in subtype of TNBC. AR positive expression was independent protective factor for recurrence and metastasis in HR +/HER2- (P = 0.033, HR = 0.653, 95% CI 0.237 to 0.986) and HR +/HER2 + breast cancer (P = 0.012, HR = 0.803, 95% CI 0.167 to 0.959), but was independent risk factors for recurrence and metastasis in TNBC (P = 0.015, HR = 4.551, 95% CI 2.668 to 8.063). AR positive expression is not an independent predictor of HR-/HER2 + breast cancer. Conclusions AR expressed the lowest in TNBC, but it could be a potential marker for the prediction of pCR in neoadjuvant therapy. AR negative patients had a higher pCR rate. AR positive expression was an independent risk factor for pCR in TNBC after neoadjuvant therapy (P = 0.017, OR = 2.758, 95% CI 1.564 to 4.013). In HR +/HER2- subtype and in HR +/HER2 + subtype, the DFS rate in AR positive patients and AR negative patients was 96.2% vs 89.0% (P = 0.001, HR = 0.330, 95% CI 0.106 to 1.034) and was 96.0% vs 85.7% (P= 0.002, HR = 0.278, 95% CI 0.082 to 0.940), respectively. However, in HR-/HER2 + and TNBC subtypes, the DFS rate in AR positive patients and AR negative patients was 89.0% vs 95.9% (P = 0.102, HR = 3.211, 95% CI 1.117 to 9.224) and 75.0% vs 93.4% (P &amp;lt; 0.001, HR = 3.706, 95% CI 1.681 to 8.171), respectively. In HR +/HER2- and HR +/HER2 + breast cancer, AR positive patients had a better prognosis, however in TNBC, AR-positive patients have a poor prognosis Citation Format: Jin Zhang. Evaluation of predictive and prognostic value of androgen receptorexpression in breast cancer subtypes treated with neoadjuvantchemotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-08-02.

Abstract PO5-09-03: Multi-tissue transcriptome-wide association studies identified genes for intrinsic subtypes of breast cancer

Abstract Background: Though several genome-wide association studies (GWAS) of breast cancer (BC) have identified common variants which differ between intrinsic subtypes, the genes through which these variants act through to impact BC risk have not been fully established. Furthermore, transcriptome-wide association studies (TWAS) have thus far been primarily employed to identify genes associated with overall BC risk, while overlooking how the influence of common variation on gene expression may contribute to subtype-specific differences. Methods: In this study, we performed two complementary multi-tissue TWASs for each of the following BC intrinsic subtypes: Luminal A-like, Luminal B-like, Luminal B/HER2-negative-like, HER2-enriched-like, Triple Negative BC. These two approaches included 1) an expression-based approach that collated TWAS signals from expression quantitative trait loci (eQTLs) across multiple tissues using the Aggregated Cauchy Association Test (ACAT) and 2) a splicing-based approach that utilized two applications of ACAT to collate splicing QTLs (sQTLs) for a given gene in a tissue and then across tissues. To perform these two TWASs, we utilized e/sQTL models trained in 11 tissues from the Genotype-Tissue Expression Project including breast, ovary, uterus, vagina, EBV-transformed lymphocytes, whole blood, spleen, liver, subcutaneous adipose, visceral adipose, and cell-cultured fibroblasts. GWAS summary statistics were previously generated from 133,384 BC cases and 113,789 controls who were participants in the Breast Cancer Association Consortium (BCAC). We further performed our TWAS while conditioning e/sQTL effect sizes on nearby GWAS index SNPs. Additionally, we utilized gene-based fine-mapping of eQTLs and sQTL to identify candidate causal genes for each intrinsic subtype. Results: Overall, we identified 164 genes in 69 loci that were associated with Luminal A-like, 19 genes in 9 loci with Luminal B-like, 18 genes in 11 loci with Luminal B/HER2-negative-like, 10 genes in 7 loci with HER2-enriched-like, and 29 genes in 12 loci with TNBC. Among these genes, 17 genes had not been reported in previous TWAS of BC, and 140 genes, 1 gene, 2 genes, 2 genes, and 16 genes were uniquely associated with each of the intrinsic subtypes, respectively. Additionally, we identified one gene associated with Luminal A-like and one gene with Luminal B-like BC that were each in a locus located at least 1.4 Mb from published GWAS hits. Furthermore, we identified 106, 11, 10, 5, and 21 candidate causal genes for each of the intrinsic subtypes, respectively, that had a posterior inclusion probability of 0.9 in at least one e/sQTL. Conclusion: In summary, our multi-tissue TWAS corroborated previous GWAS loci for overall BC risk and intrinsic subtypes, while underscoring how common variation impacts BC etiology by modulating the expression and splicing of genes in multiple tissue types. Citation Format: James Li, Julian McClellan, Haoyu Zhang, Guimin Gao, Dezheng Huo. Multi-tissue transcriptome-wide association studies identified genes for intrinsic subtypes of breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-09-03.

Abstract PO4-26-06: Identifying mutation-independent signaling pathway activation in molecular subtypes of triple negative breast cancers

Abstract Introduction Triple negative breast cancer (TNBC) is an aggressive cancer defined by the absence of estrogen receptors (ER), progesterone receptors (PR), and lack of human epidermal growth factor receptor 2 (HER-2). We previously identified molecular subgroups with distinct mutational, epigenetic, and clinicopathologic signatures. Here, we sought to identify signaling pathways using targeted RNA expression-based pathway analysis. Methods We analyzed 44 TNBC cases diagnosed at NYU Langone Health between March 2011 and April 2018. Samples were compared based on histology, immunohistochemistry, and epigenetics. We assessed mRNA expression levels of pathway-specific target genes with RT-qPCR using the OncoSIGNal pathway profiling assay. Signal transduction pathway analyses were used to measure activity of the estrogen receptor (ER), androgen receptor (AR), phosphoinositide-3-kinase (PI3K), mitogen-activated protein kinase (MAPK), Hedgehog (HH), Notch, and transforming growth factor beta (TGF- β) pathways. Results DNA methylation Cluster 1, which is enriched for apocrine histology and PI3K/Akt mutations, showed no increased activity in PI3K pathway by RNA expression, but showed increase of AR and MAPK signaling, with a single case of increased ER signaling in the absence of ESR1 activating mutations. In contrast, both DNA methylation Cluster 2 (no recurrent mutations) and Cluster 3 (DNA instability cluster) showed upregulation in PI3K pathway in 4/7 (57%) and 11/25 (44%) of cases, respectively. PI3K pathway activation was invariably associated with high Ki-67 &amp;gt;15%, however not all high Ki-67 cases showed high PI3K activity. Invasive ductal carcinoma (IDC) morphology was characterized by a nearly even split between MAPK (13/28, 46%) and PI3K (12/28, 44%), with single HH and TGF- β driven cases. In 5/28 (18%) of IDC we did not identify an upregulated pathway. Discussion We show that RNA expression-based pathway activity and mutational and epigenetic analyses provide complimentary information about the molecular landscape of TNBC. PI3K mutations are early drivers and lead to distinct epigenetic signatures, however they are not associated with increased PI3K pathway activity by RNA expression. In contrast, TNBC without PI3K mutations may show activation of the PI3K pathway in the absence of PI3K/Akt mutations. Our observation suggests that distinct biomarkers may be differently suited to predict response to PI3K inhibitors in TNBC. This may include expanding the number of patients for which PI3K/Akt pathway inhibition might be a therapeutic option, as well as explaining the lack of response in PI3K mutated tumors. Citation Format: Chanel Schroff, Lawrence Lin, Dianne van Strijp, Daniel Roses, Sigi Neerken, Freya Schnabel, Farbod Darvishian, Matija Snuderl. Identifying mutation-independent signaling pathway activation in molecular subtypes of triple negative breast cancers [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 PO4-26-06.

Abstract PO3-20-11: Among the &amp;lt; 0.1 percent of breast cancers: A case of adenoid cystic carcinoma

Abstract Among the &amp;lt; 0.1 percent of breast cancers: A case of adenoid cystic carcinoma Sera Choi, B.A., Sarah Keshwani, M.D., Andrea Madrigrano, M.D. Introduction: Adenoid cystic carcinoma in the breast (ACCB) is a rare subtype of breast cancer that accounts for &amp;lt; 0.1% of all breast-related malignancies. The majority of ACCB cases in existing literature are comprised of estrogen receptor negative, progesterone receptor negative, and human epidermal growth factor receptor 2 negative, abbreviated as triple-negative breast cancer. Although most triple negative breast cancers are aggressive in nature and prognosis, ACCB is reported to be more indolent with a favorable outcome. This disparity raises the question of whether the treatment approach for ACCB should follow the well-established treatment plan for other triple negative breast cancers given its atypical characteristics. Furthermore, while adenoid cystic carcinoma of the salivary glands is a well-known type of head and neck cancer with established treatment guidelines, there is limited data for recommendations regarding treatment for ACCB. We report a pathologically confirmed case of ACCB and review the existing literature regarding treatment strategy and prognosis. Case: This case is of a 69-year-old female who presented with an abnormal screening mammogram with a core needle biopsy confirming ACCB in the left lower outer quadrant. The patient was asymptomatic with no palpable masses, nipple discharge, or skin changes of the breast. Biopsy revealed adenoid cystic carcinoma grade 2, classic type, with immunochemistry confirming estrogen-receptor negative, progesterone-receptor negative, and human epidermal growth factor-receptor negative. After a thorough discussion of the options, the patient elected for breast conserving therapy and sentinel lymph node biopsy. Tumor was resected with negative margins and two out of two lymph nodes were negative for metastasis. The patient was recommended whole breast adjuvant radiation therapy given the large tumor size of 4.8cm. Chemotherapy was not recommended due to data that largely supports local targeted therapy over systemic treatment in patients without metastatic ACCB. The patient is continuing with routine follow-up evaluations. Discussion: Currently, mainstay treatment comprises of surgical resection with lumpectomy or mastectomy, with or without nodal evaluation. Radiation therapy is seen as beneficial in reducing recurrence and prolonging disease-free survival in ACCB. There is ongoing debate regarding the role of chemotherapy in ACCB patients, as triple-negative breast cancers are typically treated with a systemic chemotherapy regimen. However, since ACCB has a more favorable prognosis, the role of chemotherapy remains uncertain. With lack of data on ACCB, treatment modalities should be evaluated on a case-by-case basis. Moreover, considering the scarcity of information concerning this particular subtype of breast cancer, it is advisable to discuss these patients within a multi-disciplinary tumor board setting to ensure patients receive the maximum benefit. Citation Format: Sera Choi, Sarah Keshwani, Andrea Madrigrano. Among the &amp;lt; 0.1 percent of breast cancers: A case of adenoid cystic carcinoma [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-20-11.

Abstract PO3-16-04: Distribution of intrinsic subtypes in endocrine-resistant and endocrine-sensitive breast cancer

Abstract Background Breast cancer (BC) is a heterogeneous disease that can be divided into intrinsic molecular subtypes. Among the four intrinsic subtypes, Luminal A and Luminal B are the most common and associated with the best outcome, whereas HER2-enriched and basal-like are less frequent. Tumors that are estrogen receptor α (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative (ER+/HER2-) are mostly found among the luminal subtypes. Despite that patients with ER+/HER2- tumors are offered adjuvant endocrine therapy, around one-third eventually develop endocrine resistance. The aim of this study was to explore the distribution of intrinsic subtypes in endocrine-resistant primary and relapse tumors, comparing these to endocrine-sensitive controls. Materials and methods Verified endocrine-resistant BC patients diagnosed in 2008-2012 were retrospectively collected at the Karolinska University Hospital, Stockholm, Sweden. Cases (N=70) were identified as patients with ER+/HER2- primary tumors and subsequent ER+/HER2- relapse tumors within 5 years and during endocrine therapy. Patients with primary ER+/HER2- tumors without progression or relapse at 10 years of follow-up were defined as controls (N=78), diagnosed in 2005-2006. Extracted RNA from formalin-fixed paraffin-embedded tumor tissue was analyzed by Affymetrix Clariom D Microarray and assessed by Transcriptome Analysis Console and R software. Results Among the controls, the distribution of Luminal A, Luminal B, and HER2-enriched subtypes was 65.4%, 34.6%, and 0%, respectively. In primary tumors, the distribution was in turn 55.4%, 43.1%, and 1.5%, and among relapse tumors 57.6%, 37.9%, and 4.5%, respectively. A total of 19 cases, accounting for 27.1%, switched intrinsic subtypes between the paired primary and relapse tumors. No tumors exhibited the basal-like subtype. Conclusion In this unique cohort, Luminal B and HER2-enriched subtypes were more common in primary and relapse tumors of verified endocrine-resistant patients than in primary tumors of endocrine-sensitive controls. Further, the HER2-enriched subtype, although sparse, was more frequently found in patients’ relapse tumors than in their corresponding primary tumors, and over one-fourth of cases switched subtypes during progression. These findings support the presence of subtype shifting in endocrine-resistant relapses and that endocrine-resistant tumors are more prone to be of Luminal B or HER2-enriched subtypes than endocrine-sensitive tumors. Citation Format: Caroline Schagerholm, Stephanie Robertson, Emelie Karlsson, Emmanouil Sifakis, Johan Hartman. Distribution of intrinsic subtypes in endocrine-resistant and endocrine-sensitive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-16-04.

Abstract PO5-16-07: Unveiling the Landscape of PD-L1 Expression and Tumor-Infiltrating Lymphocyte Subtypes in Advanced Triple-Negative Breast Cancer

Abstract Background: Triple-negative breast cancer (TNBC) is known for its aggressive behavior with poor survival outcomes. Influenced by different expression levels of Programmed Death-Ligand 1 (PD-L1) and several subtypes of tumor-infiltrating lymphocytes (TILs), tumor microenvironment (TME) plays a crucial role in TNBC response to treatment and progression. Objective: To assess the prevalence and prognostic role of PD-L1 expression in advanced TNBC, defined as unresectable stage III or stage IV disease, in patients treated with a standard cytotoxic chemotherapy regimen. TILs composition was also evaluated as an exploratory objective. Methods: The internal database of the Brazilian National Cancer Institute was queried out for women diagnosed and treated with advanced TNBC from January 2018 to December 2022. Formalin-fixed paraffin-embedded samples of a maximum of four years old were analyzed. PD-L1 expression using 22C3 pharmDX assay was estimated through combined positive score (CPS) dichotomization (CPS &amp;lt; 10 vs. CPS≥10). Tissue microarrays comprising the samples of biopsies were subjected to immunohistochemistry, targeting specific markers including CD3, CD4, CD8, CD56, CD68, CD117, FOXP3, PD-1, the immune cell profiles were carefully examined and their correlation with the PD-L1 CPS was determined. Results: A total of 150 patients were included. The expression of PD-L1 was undetermined in 2 cases. The median age was 51.5 years (IQR 41.8-60.2) and 20.9% of the cases had CPS≥10. Most patients were &amp;lt; 65 years (73.0%), were postmenopausal (56.8%) and belonged to non-white ethnicity (70.3%). Postmenopausal women predominated in the CPS≥10 subgroup (74.2%) (Table 1). No significant differences in demographic characteristics and clinicopathological variables were observed based on PD-L1 subgroups, 117 patients (79.1%) had CPS &amp;lt; 10, with 91 (77.8%) being de novo stage IV metastatic disease. CD3+ (p=0.037), CD4+ (p=0.005) and CD8+ (p=0.001) TILs had higher expression in tumors with PD-L1 CPS≥10 (Table 2). According to the treatment received, almost half of the patients only received first-line chemotherapy (47%), as the following second line was applied to 28.8% of the total group. The third and fourth lines were administered in 12.9% and 9.1% of patients, respectively. Only 2 patients went through five palliative chemotherapy lines, and only one received up to 6 treatment lines. Between the subgroups CPS≥10 versus CPS &amp;lt; 10 no statistically significant differences were observed in the median progression-free survival (PFS) (5.1 vs. 5.0 months, p=0.89) and overall survival (OS) (8.7 vs. 8.8 months, p=0.6). Conclusion: This study offers insights into the expression patterns of PD-L1 and TILs subtypes in advanced TNBC cases in Brazil. PD-L1 CPS did not influence survival outcomes for this cohort of patients treated with cytotoxic chemotherapy only. The composition of TILs subtypes within the TME appears to vary based on PD-L1 CPS. Table 1. Advanced TNBC population characteristic by CPS (Nf148). Table 2. Tumor Infiltrating Lymphocytes characterization (CD3, CD4, CD8, CD56, CD68, CD 117, FOXP3 and PD-1) and its correlation with CPS status. Citation Format: Alexssandra Lima Siqueira dos Santos, Jesse Lopes da Silva, Lucas Zanetti de Albuquerque, Antônio Lucas Araújo Neto, Cecília Ferreira da Silva, Luana Aguiar Mesquita Cerva, Isabele Ávila Small, Cicera Pimenta Marcelino, Paula de Mendonça Batista, Maria Aparecida do Carmo Rego, Maria Amélia Carlos Souto Maior Borba, Andreia Cristina de Melo. Unveiling the Landscape of PD-L1 Expression and Tumor-Infiltrating Lymphocyte Subtypes in Advanced 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 PO5-16-07.

Abstract PO4-16-03: Ectopic expression of lineage-specific transcription factors in Breast Cancer

Abstract Background: Lineage-specific transcription factors (LTFs) are purported to define cellular lineages and their expression could be used to identify subtypes of cancer. In many cancers, tuft cell differentiation appears to have prognostic impact. However, such differentiation has not been documented in breast cancer. Methods: We sought to study the fidelity of LTFs (MYOG, POU2F3, FOXA1, FOXA2, FOXA3, FOXJ1, HNF4A, HNF4G, SPIB, SOX8, GRHL1, GRHL2, and GRHL3) for their presence and prognostic impact in breast cancer. Single cell RNA data from GSE 161529, which contains 421,761 single cells, was downloaded and analyzed for the expression and co-expression of LTFs. The data was first subdivided based on ER+ and TNBC status. Analysis was performed using cells from 10ER+ samples and 4 TNBC samples. Cell clustering using Louvain’s method was run using all genes. Cell type assignment was then performed using well-known markers for both tumor and lymphocyte marker from existing publications. Further analysis was restricted to keratin expressing cells and to study the presence and co-expression of LTFs in the epithelial cells. KM-Plotter was employed to determine the prognostic value of these LTFs. The analysis was further stratified by expression of estrogen receptor positive and negative status. The endpoint of relapse free survival was used, as it provided data on the largest number of patients. Results: Single-cell analysis pipeline successfully identified distinct populations of tumor epithelial cells accompanied by various lymphocytes, including B cells, CD8+ T cells, CD4+ T cells, dendritic cells, and macrophages, in both ER+ tumors and TNBC tumor samples. We further confirmed the expression of the LTFs in the epithelial (keratin+) compartment. Expression of all LTFs (except MYOG, and FOXA2) was scattered in the different epithelial clusters. Further analysis of single LTFs showed differentiational co-expression based on ER+ status. POU2F3+/ER+ cells also co-expressed FOXA1 and GRHL1 while POU2F3+/ER- cells were GRHL1+ and (weak) SPIB+. The analysis of LTFs using KM-Plotter tool revealed their expression documenting multiple cell lineages in breast cancer; this was noted in ER+, HER2+ cancers and TNBCs. The directionality of the outcome (good or bad prognosis) varied with the specific TFs and subtype of breast cancer. High expression of POU2F3, and FOXA1, and SPIB were associated with better relapse-free survival (RFS) in ER+ breast cancer. POU2F3, FOXA2, FOXA3 were associated with worse RFS, whereas SPIB was with prognosis in ER- breast cancers. Conclusions: We for the first time document the expression of LTFs in breast cancer and their prognostic relevance based on ER+ and ERneg status. Expression of POU2F3, a marker of tuft cells which are known to regulate immune response, was noted to be associated with improved outcomes in ER+ tumors. Further characterization of the relevance of LTFs and their co-expression with respect to therapeutic response is ongoing. Citation Format: Sunil Badve, Jian Hu, Yu Zhang, Yesim Gokmen-Polar. Ectopic expression of lineage-specific transcription factors in Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-16-03.