Non-luminal Tumors Research Articles

Potential of PSMA for breast cancer in nuclear medicine: digital quantitative immunohistochemical analysis and implications for a theranostic approach

BackgroundFurther research is still needed to fully understand the potential of prostate-specific membrane antigen (PSMA) in breast cancer (BC) and to develop and optimize targeted therapies and imaging modalities. The objective of this study was to present a comprehensive analysis of immunohistochemistry data on PSMA staining in BC and to discuss its potential value in a theranostic approach.MethodsFifty-eight male and female patients were randomly selected from a retrospective database of patients who underwent surgery for breast cancer between January 2012 and December 2017 and for whom a specimen is available in our tumour library. Immunodetection of PSMA and CD31 was performed on serial slides. The digitized slides were reviewed and analysed by an experienced pathologist. Additionally, the corresponding TIFF images were processed to calculate the percentage of positive neovessels.ResultsEighteen patients (31.6%) had no expression, 29 (50.9%) had PSMA neovascular expression scored as “1”, and 10 (17.5%) had neovascular expression scored as “2”. Digital immunohistochemistry analysis for this last specific group of patients showed a median proportion of positive neovessels equal to 5% (range: 3–19). A multivariable logistic regression demonstrated that the odds of PSMA positivity were 4.55 times higher in non-luminal tumours and decreased by a factor of 0.12 in lobular subtypes. There was no association between sex or the presence of a germline BRCA1/2 mutation and PSMA expression in tumours.ConclusionsOur study highlights generally low neovascular expression of PSMA in specific histopathological subtypes of breast cancer, which will likely hamper the development of an adequate theranostic strategy.Trial registrationThe procedure has been retrospectively registered to the French National Institute for Health Data (N° F20220615153900).

PD-L1 protein expression in breast cancer

AimsThe immune checkpoint marker, Programmed cell death-ligand 1 (PD-L1), is expressed by both cancer epithelial cells and tumour-infiltrating immune cells (TICs) thus constituting a potential target for immunotherapy. This is...

The Clinicopathological and Prognostic Significance of the Expression of PD-L1 and MET Genes in Breast Cancer: Potential Therapeutic Targets.

The heterogeneity of breast cancer requires exploring novel prognostic biomarkers as well as therapeutic targets for the treatment of the disease. The METABRIC dataset was used to describe the gene expression of the programmed death-ligand 1 (PD-L1) and the hepatocyte growth factor receptor (MET) and their association with the tumor clinicopathologic characteristics and overall survival in breast cancer. The expression of the PD-L1 and MET genes correlated positively with the Nottingham Prognostic Index (NPI) (p=0.003 and p < 0.001, respectively). The expression of the two genes correlated inversely with luminal A and luminal B tumors (r= - 0.089, p= 0.021 and r= - 0.116, p= 0.013, respectively). The PD-L1 mRNA levels were significantly higher in hormone receptor-negative and HER2-positive tumors. MET mRNA expression levels were significantly higher in hormone receptor-negative, HER2-enriched, and non-luminal breast cancers. The PD-L1/MET double-high expression was associated with younger age of patients at diagnosis, higher NPI scores, larger tumors, advanced stage, high-grade, hormone receptor-negativity, HER2-positivity, and non-luminal tumors. None of the genes or their double expression status was significantly associated with overall survival in this analysis. The expression of the PD-L1 and MET genes is remarkably associated with worse tumor clinicopathologic features and poor prognosis in patients with breast cancer. Further investigations using combination drug regimens targeting PD-L1 and MET are important, particularly in breast tumors expressing high levels of both proteins.

Machine learning radiomics based on intra and peri tumor PA/US images distinguish between luminal and non-luminal tumors in breast cancers

PurposeThis study aimed to evaluate a radiomics model using Photoacoustic/ultrasound (PA/US) imaging at intra and peri-tumoral area to differentiate Luminal and non-Luminal breast cancer (BC) and to determine the optimal peritumoral area for accurate classification. Materials and methodsFrom February 2022 to April 2024, this study continuously collected 322 patients at Shenzhen People’s Hospital, using standardized conditions for PA/US imaging of BC. Regions of interest were delineated using ITK-SNAP, with peritumoral regions of 2 mm, 4 mm, and 6 mm automatically expanded using code from the Pyradiomic package. Feature extraction was subsequently performed using Pyradiomics. The study employed Z-score normalization, Spearman correlation for feature correlation, and LASSO regression for feature selection, validated through 10-fold cross-validation. The radiomics model integrated intra and peri-tumoral area, evaluated by receiver operating characteristic curve(ROC), Calibration and Decision Curve Analysis(DCA). ResultsWe extracted and selected features from intratumoral and peritumoral PA/US images regions at 2 mm, 4 mm, and 6 mm. The comprehensive radiomics model, integrating these regions, demonstrated enhanced diagnostic performance, especially the 4 mm model which showed the highest area under the curve(AUC):0.898(0.78–1.00) and comparably high accuracy (0.900) and sensitivity (0.937). This model outperformed the standalone clinical model and combined clinical-radiomics model in distinguishing between Luminal and non-Luminal BC, as evidenced in the test set results. ConclusionThis study developed a radiomics model integrating intratumoral and peritumoral at 4 mm region PA/US model, enhancing the differentiation of Luminal from non-Luminal BC. It demonstrated the diagnostic utility of peritumoral characteristics, reducing the need for invasive biopsies and aiding chemotherapy planning, while emphasizing the importance of optimizing tumor surrounding size for improved model accuracy.

Predictive value of ultrasound doppler parameters in neoadjuvant chemotherapy response of breast cancer: Prospective comparison with magnetic resonance and mammography.

Neoadjuvant chemotherapy (NACT) is a treatment option for breast cancer patients that allows for the assessment of tumor response during treatment. This information can be used to adjust treatment and improve outcomes. However, the optimal imaging modalities and parameters for assessing tumor response to NACT are not well established. This study included 173 breast cancer patients who underwent NACT. Patients were imaged with ultrasound (US), mammography (MMG), and magnetic resonance imaging (MRI) at baseline, after two cycles of NACT, and before breast surgery. US parameters included lesion morphology, Doppler variables, and elastography measurements. MMG and MRI were evaluated for the presence of nodules and tumor dimensions. The pathological response to NACT was determined using the residual cancer burden (RCB) classification. The US parameter with the highest power for predicting pathological complete response (pCR) was shear wave elastography (SWE) maximum speed inside the tumor at baseline. For nonluminal tumors, the end diastolic velocity measured by US after two cycles of NACT showed the highest predictive value for pCR. Similarly, SWE maximum speed after two cycles of NACT had the highest discriminating power for predicting RCB-III in luminal tumors, while the same parameter measured at baseline was most predictive for nonluminal tumors. This study provides evidence that mid-treatment Doppler US and other imaging modalities can be used to predict the response to NACT in breast cancer patients. Functional parameters, such as blood flow velocities and SWE measurements, demonstrated superior predictive value for pCR, while morphological parameters had limited value. These findings have implications for personalized treatment strategies and may contribute to improved outcomes in the management of breast cancer.

Abstract PO1-06-02: Solti-1716 TATEN phase II trial: Targeting non-Luminal disease by PAM50 with pembrolizumab and paclitaxel in Hormone Receptor-positive/HER2-negative advanced breast cancer (ABC)

Abstract Background Within HR+/HER2-negative breast cancer, PAM50 non-luminal tumors (HER2-enriched [HER2-E] and Basal-like) have higher expression of proliferation and immune-related genes and tumor infiltrating lymphocytes and might benefit from immunotherapy. Here, we report the efficacy, safety, and correlative analysis data of the TATEN trial, the first study designed to evaluate pembrolizumab and paclitaxel in HR+/HER2-negative, PAM50 non-luminal, ABC. Methods TATEN trial (NCT04251169) is a single-arm, multicenter, phase II study evaluating pembrolizumab in combination with paclitaxel in patients with HR+/HER2-, PAM50 non-luminal ABC. Key inclusion criteria include progression to prior CDK4/6 inhibitors (CDK4/6i), presence of measurable disease, no prior chemotherapy for ABC, ECOG 0-1, and non-luminal metastatic disease by PAM50. Included patients received pembrolizumab at 200 mg every 3 weeks (beginning at cycle 1) in combination with weekly paclitaxel at 80 mg/m2 beginning at cycle 2. The primary endpoint was overall response rate (ORR) according to RECIST V1.1. in patients who received at least one dose of combination treatment and had a first, post-baseline tumor assessment (evaluable population). Secondary endpoints included progression-free survival (PFS), clinical benefit rate (CBR), safety, and predictive biomarkers. The study was based on a Simon two-stage design. Stage I of the trial would be considered successful if at least 6 of 15 patients achieved a partial response and/or complete response. In that case, the trial would recruit up to 46 evaluable patients for a target ORR ≥ 41%. Metastatic biopsies from patients enrolled in pre-screening were also evaluated for tumor infiltrating lymphocytes (TILs) and were further analyzed with an expression panel of 192 genes, including PDL1 and PD1. Results From July 2020 to December 2021, 132 tumors were screened, and 27 PAM50 non-luminal tumors were identified (20%). Non-luminal tumors trended to have higher PDL1 expression (p=0.090) and TILs (p=0.084) compared to luminal tumors, while no difference was observed for PD1 (p=0.850). Of 20 recruited patients in the study (stage I+II), 18 were evaluable for the primary endpoint. Baseline characteristics were as follows: median age 55 years, ECOG 0 55%, de novo MBC 22%, and visceral disease 72.2%. Eleven patients had received paclitaxel treatment in the adjuvant setting. Regarding PAM50 subtype, 2 patients had basal-like and 16 HER2-E tumors. At the time of data cut-off (June 2023), 13 patients (72.2%) had stopped their treatment because of progressive disease and 3 (16.6%) due to toxicity. Two patients (11.1%) were still on treatment. The ORR was 61.1 % (11 of 18, 95% CI 35.7-82.7). CBR was 88.9% (16 of 18, 95% CI 65.3-98.6), and median PFS was 8.3 months (95% CI 7.3 – 14.1). Treatment-related adverse events (TRAEs) of any grade (G) occurred in 19 patients (95%), while 45% of patients experienced G3 TRAEs. No G4 or G5 TRAEs were reported in the evaluable population. Gene expression analysis was successful for all recruited patients (n=20). High expression of the PAM50 luminal A signature (p=0.049), and the luminal genes PGR (p=0.028) and RRAGA (p=0.038) were associated with worse PFS (univariate analyses). The pan-leucocyte receptor CD84 (p=0.028) was associated with better PFS (univariate analysis). Conclusions Pembrolizumab in combination with paclitaxel is safe and exhibits promising efficacy outcomes in patients with CDK4/6i resistant HR+/HER2- ABC with a PAM50 non-luminal subtype. Although meeting the criteria for stage II, the enrollment was stopped prematurely due to the lack of funding and pembrolizumab supply. More correlative analyses will be presented at the conference. This study was funded in part by MSD. Citation Format: Aleix Prat, Benedetta Conte, Fara Brasó-Maristany, Nuria Chic, Montserrat Muñoz, Cristina Hernando, Manuel Alva, Silvia Vazquez, Salvador Blanch, Mafalda Oliveira, Esther Fernández, Oleguer Castillo, Patricia Galván, Ángela Aguirre, Esther Sanfeliu, Lorea Villanueva, Tomás Pascual, Eva Ciruelos. Solti-1716 TATEN phase II trial: Targeting non-Luminal disease by PAM50 with pembrolizumab and paclitaxel in Hormone Receptor-positive/HER2-negative advanced breast cancer (ABC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-06-02.

Evaluation of molecular subtypes of breast cancer using MRI BI-RADS Lexicon

BackgroundMolecular subtyping of breast cancer is one of the prognostic factors which play a very important role in managing patient’s treatment plan. The MRI BI-RADS Lexicon is initially used to categorize breast lesions but recent attempts were employed to differentiate breast lesions based on their molecular subtypes using this lexicon. The study aimed to evaluate of the role of the MRI BI-RADS Lexicon in classifying different molecular subtypes of breast cancer especially after coupling with Kaiser scoring system.MethodsThis retrospective study was conducted on 147 patients with 170 malignant breast lesions. They underwent Pre-contrast and a Dynamic contrast MRI study. Retrospective interpretation of the morphological and dynamic criteria of the breast lesions based on the MRI BI-RADS criteria was carried out followed by reassessment of the same lesions by Kaiser scoring. Resulting data were correlated with histopathological and immunological characterization.ResultsLuminal subtypes were more frequently encountered as mass lesions, contrary to the Non-Luminal lesions which showed a more frequent non-mass presentation value (P 0.002). The shape, margin, internal enhancement pattern of the mass lesions showed significant variability between different molecular subtypes (P < 0.001, < 0.001, < 0.001) respectively. On Dynamic study, Plateau curve was a more evident pattern with Luminal lesions contrasting with their Non-Luminal counterparts which showed a washout pattern more frequently (P 0.0004). Most of luminal A cancers were presented as mass lesions with rim enhancement and categorized as BIRADS 4 while most of Her2neu positive cancers (including luminal B entity) were presented as non-mass lesions with irregular shape and dark internal septations and categorized as BIRADS 5 with statistically significant values (P < 0.001). Coupling with Kaiser scoring system improved the categorization of non-luminal tumors as BIRADS 5 lesions especially the aggressive TN cancers.ConclusionsMRI-BIRADS lexicon can be of great value in the non-invasive molecular characterization of breast cancer. Kaiser score improved the categorization of TN cancers which were upgraded to BIRADS 5 category.

Endocrine-Sensitive Disease Rate in Postmenopausal Patients With Estrogen Receptor–Rich/ERBB2-Negative Breast Cancer Receiving Neoadjuvant Anastrozole, Fulvestrant, or Their Combination

Adding fulvestrant to anastrozole (A+F) improved survival in postmenopausal women with advanced estrogen receptor (ER)-positive/ERBB2 (formerly HER2)-negative breast cancer. However, the combination has not been tested in early-stage disease. To determine whether neoadjuvant fulvestrant or A+F increases the rate of pathologic complete response or ypT1-2N0/N1mic/Ki67 2.7% or less residual disease (referred to as endocrine-sensitive disease) over anastrozole alone. A phase 3 randomized clinical trial assessing differences in clinical and correlative outcomes between each of the fulvestrant-containing arms and the anastrozole arm. Postmenopausal women with clinical stage II to III, ER-rich (Allred score 6-8 or >66%)/ERBB2-negative breast cancer were included. All analyses were based on data frozen on March 2, 2023. Patients received anastrozole, fulvestrant, or a combination for 6 months preoperatively. Tumor Ki67 was assessed at week 4 and optionally at week 12, and if greater than 10% at either time point, the patient switched to neoadjuvant chemotherapy or immediate surgery. The primary outcome was the endocrine-sensitive disease rate (ESDR). A secondary outcome was the percentage change in Ki67 after 4 weeks of neoadjuvant endocrine therapy (NET) (week 4 Ki67 suppression). Between February 2014 and November 2018, 1362 female patients (mean [SD] age, 65.0 [8.2] years) were enrolled. Among the 1298 evaluable patients, ESDRs were 18.7% (95% CI, 15.1%-22.7%), 22.8% (95% CI, 18.9%-27.1%), and 20.5% (95% CI, 16.8%-24.6%) with anastrozole, fulvestrant, and A+F, respectively. Compared to anastrozole, neither fulvestrant-containing regimen significantly improved ESDR or week 4 Ki67 suppression. The rate of week 4 or week 12 Ki67 greater than 10% was 25.1%, 24.2%, and 15.7% with anastrozole, fulvestrant, and A+F, respectively. Pathologic complete response/residual cancer burden class I occurred in 8 of 167 patients and 17 of 167 patients, respectively (15.0%; 95% CI, 9.9%-21.3%), after switching to neoadjuvant chemotherapy due to week 4 or week 12 Ki67 greater than 10%. PAM50 subtyping derived from RNA sequencing of baseline biopsies available for 753 patients (58%) identified 394 luminal A, 304 luminal B, and 55 nonluminal tumors. A+F led to a greater week 4 Ki67 suppression than anastrozole alone in luminal B tumors (median [IQR], -90.4% [-95.2 to -81.9%] vs -76.7% [-89.0 to -55.6%]; P < .001), but not luminal A tumors. Thirty-six nonluminal tumors (65.5%) had a week 4 or week 12 Ki67 greater than 10%. In this randomized clinical trial, neither fulvestrant nor A+F significantly improved the 6-month ESDR over anastrozole in ER-rich/ERBB2-negative breast cancer. Aromatase inhibition remains the standard-of-care NET. Differential NET response by PAM50 subtype in exploratory analyses warrants further investigation. ClinicalTrials.gov Identifier: NCT01953588.

BRAF Expression and Copy Number Alterations Predict Unfavorable Tumor Features and Adverse Outcomes in Patients With Breast Cancer.

Background: The role of BRAF in breast cancer pathogenesis is still unclear. To address this knowledge gap, this study is aimed at evaluating the impact of BRAF gene expression and copy number alterations (CNAs) on clinicopathologic characteristics and survival in patients with breast cancer. Methods: The Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) dataset was obtained from the cBioPortal public domain. Tumoral BRAF mRNA expression and CNAs along with demographic and tumor data for patients with breast cancer were retrieved. The association of BRAF expression and CNAs with breast cancer clinicopathologic characteristics was analyzed. The impact of BRAF mRNA expression on the overall survival of patients was assessed using Kaplan-Meier survival analysis. Results: BRAF gene mRNA log intensity expression was positively correlated with tumor size and the Nottingham Prognostic Index (NPI) (p < 0.001). Alternatively, BRAF gene expression was negatively correlated with the age at diagnosis (p = 0.003). The average BRAF mRNA expression was significantly higher in premenopausal patients, patients with high tumor grade, hormone receptor-negative status, and non-luminal tumors compared to postmenopausal patients, patients with low-grade, hormone receptor-positive, and luminal disease. BRAF gain and high-level amplification copy numbers were significantly associated with higher NPI scores and larger tumor sizes compared to neutral copy number status. Survival analysis revealed no discernible differences in overall survival for patients with low and high BRAF mRNA expression. Conclusion: High BRAF mRNA expression as well as the gain and high-level amplification copy numbers were associated with advanced tumor characteristics and unfavorable prognostic factors in breast cancer. BRAF could be an appealing target for the treatment of premenopausal patients with hormone receptor-negative breast cancer.

Association of PIK3CA Mutation With Pathologic Complete Response and Outcome by Hormone Receptor Status and Intrinsic Subtype in Early-Stage ERBB2/HER2-Positive Breast Cancer

PIK3CA mutations may be associated with outcomes of patients with ERBB2/HER2-positive early breast cancer (EBC). To assess if PIK3CA mutations among patients with ERBB2/HER2-positive EBC are associated with treatment response and outcome, and if these associations vary by hormone receptor (HR) status or intrinsic molecular subtype (IMS). This cohort study derived data on 184 patients from the phase 3 neoadjuvant Cancer and Leukemia Group B (CALGB) 40601 trial that enrolled patients with ERBB2/HER2-positive EBC in North America between January 1, 2008, and December 31, 2012. Participants received neoadjuvant paclitaxel with trastuzumab, lapatinib, or both. Statistical analysis was performed from March 23, 2022, to March 9, 2023. Gene expression profiling by RNA sequencing with Prediction Analysis of Microarray 50-determined IMS and PIK3CA mutations from whole-exome sequencing were obtained from pretreatment biopsies from 184 of 305 trial participants. The primary end point was pathologic complete response (pCR) and the secondary end point of event-free survival (EFS). The association of PIK3CA mutations with pCR and EFS by HR status and IMS was estimated using logistic and Cox proportional hazards regression models. All 184 participants were women, with a median age of 49 years (range 24-75 years). A total of 121 participants (66%) had clinical stage II tumors; 32 (17%) had PIK3CA mutations, most frequently H1047R (38% [12 of 32]) and E545K (22% [7 of 32]). PIK3CA mutations were present in 20 of 102 cases of HR-positive EBC (20%) and 12 of 82 cases HR-negative EBC (15%) and varied by IMS (luminal B, 9 of 25 [36%]; luminal A, 2 of 21 [10%]; and ERBB2/HER2-enriched tumors, 19 of 102 [19%]). Pathologic complete response rates were lower in PIK3CA mutated than PIK3CA wild type in the overall population (34% [11 of 32] vs 49% [74 of 152]; P = .14) and were significantly different among those receiving trastuzumab (30% [7 of 23] vs 54% [63 of 117]; P = .045). At a median follow-up of 9 years, PIK3CA mutations were significantly associated with worse EFS in the overall cohort (hazard ratio, 2.58 [95% CI, 1.24-5.35]; P = .01), which persisted in a multivariable model including pCR, HR status, stage, and IMS (hazard ratio, 2.52 [95% CI, 1.16-5.47]; P = .02). The negative association of PIK3CA mutation was significant in HR-positive (hazard ratio, 3.60 [95% CI, 1.45-8.96]; P = .006) and luminal subtypes (hazard ratio, 4.84 [95% CI, 1.08-21.70]; P = .04), but not in nonluminal and HR-negative tumors. In ERBB2/HER2-positive EBC, PIK3CA mutations were associated with lower pCR rates and independently associated with worse long-term EFS. These findings appear to be associated with PIK3CA mutations in HR-positive and luminal EBC.

Abstract B070: Characterizing breast cancer etiologic subtypes in the Ghana Breast Health Study

Abstract Background: Breast cancer subtyping has largely been based on immunohistochemical markers of estrogen receptor status. However, RNA-based intrinsic subtypes, including luminal (hormone receptor-positive) and non-luminal (hormone receptor-negative) have been shown to be etiologically relevant, with studies also suggesting other tumor markers (e.g., TP53 status) to be important contributors to etiologic heterogeneity. Compared to luminal tumors, non-luminal tumors are more likely to be TP53 mutant than wildtype-like. TP53 mutant breast cancers are associated with more aggressive tumor features and these mutations are more common among cases of African descent. However, few RNA-based subtyping studies have described etiologic heterogeneity in indigenous African populations. Therefore, we evaluated associations between established breast cancer risk factors and risk of PAM50 intrinsic subtypes and tumor subtypes defined by RNA-based TP53 functional status in the population-based Ghana Breast Health Study (GBHS). Methods: We analyzed data from 600 invasive breast cancer cases and 2,528 controls in the GBHS. RNA was extracted from formalin-fixed paraffin-embedded tumor samples and run on the nCounter® Breast Cancer 360™ Panel. Samples were then classified for intrinsic subtype (N=285 luminal, N=315 non-luminal) using a research version of the PAM50 assay and for TP53 functional status (N=333 wildtype-like, N=300 mutant-like) using a validated RNA signature. Odds ratios (OR) and 95% confidence intervals (CI) were estimated for risk factors using polytomous logistic regression models adjusted for potential confounders. Results: About 1 in 4 tumors classified as ER-positive by immunohistochemistry were non-luminal by RNA expression. Similarly, about 1 in 5 ER-negative tumors were reclassified as luminal. Etiologic heterogeneity was observed by luminal subtype for certain reproductive factors. Higher parity (≥3 vs. &amp;lt;3 births) was associated with lower risk of luminal tumors (OR [95% CI] = 0.68 [0.49, 0.92]), but not with non-luminal tumors (0.95 [0.69, 1.30]). Likewise, later age at first birth (≥26 vs. &amp;lt;19 years) was more strongly associated with risk of luminal than non-luminal tumors (2.16 [1.37, 3.40] and 1.30 [0.84, 2.00], respectively). Consistent with previous findings, TP53 status was also an important etiologic factor and risk factor patterns mirrored those for luminal/non-luminal subtypes. Finally, we evaluated cross-classification of these two etiologic markers to identify risk factors that represent the dual action of both an estrogenic and a DNA-repair pathway. Age at first birth seems to suggest dual action. Conclusions: This study used high-quality RNA expression data to show that intrinsic subtype and TP53 status are useful breast tumor markers for describing etiologic heterogeneity, with cross-classification leading to improved understanding of the etiologic underpinnings of certain risk factors. This work has important implications for the use of gene-expression-based subtyping for breast cancer classification in this population. Citation Format: Amber N. Hurson, Ebonee N. Butler, Alina M. Hamilton, Bernard Petershie, Thomas U. Ahearn, Melissa A. Troester, Jonine Figueroa, Nicolas Titiloye, Montserrat Garcia-Closas, Mustapha Abubakar. Characterizing breast cancer etiologic subtypes in the Ghana Breast Health Study [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr B070.

Deep learning radiopathomics based on preoperative US images and biopsy whole slide images can distinguish between luminal and non-luminal tumors in early-stage breast cancers.

For patients with early-stage breast cancers, neoadjuvant treatment is recommended for non-luminal tumors instead of luminal tumors. Preoperative distinguish between luminal and non-luminal cancers at early stages will facilitate treatment decisions making. However, the molecular immunohistochemical subtypes based on biopsy specimens are not always consistent with final results based on surgical specimens due to the high intra-tumoral heterogeneity. Given that, we aimed to develop and validate a deep learning radiopathomics (DLRP) model to preoperatively distinguish between luminal and non-luminal breast cancers at early stages based on preoperative ultrasound (US) images, and hematoxylin and eosin (H&E)-stained biopsy slides. This multicentre study included three cohorts from a prospective study conducted by our team and registered on the Chinese Clinical Trial Registry (ChiCTR1900027497). Between January 2019 and August 2021, 1809 US images and 603H&E-stained whole slide images (WSIs) from 603 patients with early-stage breast cancers were obtained. A Resnet18 model pre-trained on ImageNet and a multi-instance learning based attention model were used to extract the features of US and WSIs, respectively. An US-guided Co-Attention module (UCA) was designed for feature fusion of US and WSIs. The DLRP model was constructed based on these three feature sets including deep learning US feature, deep learning WSIs feature and UCA-fused feature from a training cohort (1467 US images and 489 WSIs from 489 patients). The DLRP model's diagnostic performance was validated in an internal validation cohort (342 US images and 114 WSIs from 114 patients) and an external test cohort (279 US images and 90 WSIs from 90 patients). We also compared diagnostic efficacy of the DLRP model with that of deep learning radiomics model and deep learning pathomics model in the external test cohort. The DLRP yielded high performance with area under the curve (AUC) values of 0.929 (95% CI 0.865-0.968) in the internal validation cohort, and 0.900 (95% CI 0.816-0.953) in the external test cohort. The DLRP also outperformed deep learning radiomics model based on US images only (AUC 0.815 [0.719-0.889], p<0.027) and deep learning pathomics model based on WSIs only (AUC 0.802 [0.704-0.878], p<0.013) in the external test cohort. The DLRP can effectively distinguish between luminal and non-luminal breast cancers at early stages before surgery based on pretherapeutic US images and biopsy H&E-stained WSIs, providing a tool to facilitate treatment decision making in early-stage breast cancers. Natural Science Foundation of Guangdong Province (No. 2023A1515011564), and National Natural Science Foundation of China (No. 91959127; No. 81971631).

S100A8 gene copy number and protein expression in breast cancer: associations with proliferation, histopathological grade and molecular subtypes

Background and aimsAmplification of S100A8 occurs in 10–30% of all breast cancers and has been linked to poorer prognosis. Similarly, the protein S100A8 is overexpressed in a roughly comparable proportion of breast cancers and is also found in infiltrating myeloid-lineage cells, again linked to poorer prognosis. We explore the relationship between these findings.MethodsWe examined S100A8 copy number (CN) alterations using fluorescence in situ hybridization in 475 primary breast cancers and 117 corresponding lymph nodes. In addition, we studied S100A8 protein expression using immunohistochemistry in 498 primary breast cancers from the same cohort.ResultsWe found increased S100A8 CN (≥ 4) in tumor epithelial cells in 20% of the tumors, increased S100A8 protein expression in 15%, and ≥ 10 infiltrating S100A8 + polymorphonuclear cells in 19%. Both increased S100A8 CN and protein expression in cancer cells were associated with high Ki67 status, high mitotic count and high histopathological grade. We observed no association between increased S100A8 CN and S100A8 protein expression, and only a weak association (p = 0.09) between increased CN and number of infiltrating S100A8 + immune cells. Only S100A8 protein expression in cancer cells was associated with significantly worse prognosis.ConclusionsAmplification of S100A8 does not appear to be associated with S100A8 protein expression in breast cancer. S100A8 protein expression in tumor epithelial cells identifies a subgroup of predominantly non-luminal tumors with a high mean age at diagnosis and significantly worse prognosis. Finally, S100A8 alone is not a sufficient marker to identify infiltrating immune cells linked to worse prognosis.

Study of anemia in non-luminal solid tumors

Background: Anemia is particularly prevalent in India due to widespread malnutrition. Cancer related anemia affects about three-fourths of cancer patients, causing symptoms like fatigue, appetite loss, and difficulty concentrating, and can worsen cancer prognosis, lengthen treatment, and reduce survival rates. Anemia is a significant cause of tumor hypoxia, which exacerbates the side effects of radiotherapy and chemotherapy, and affects energy levels and emotional distress. Methods: The present cross-sectional study aims to assess the prevalence and types of anemia in patients with newly diagnosed non-luminal solid tumors. The study sample included all patients meeting the inclusion criteria, with a sample size of 100. Clinical evaluation and investigations were carried out to determine the presence and severity of anemia. Data was compiled and analyzed. Results: Of the 100 patients enrolled, 68% had evidence of anemia, and the majority of them were in the age group of 51-60 years. Anemia’s association with body mass index (BMI) was noted and was more common in underweight and normal-weight patients. The commonest malignancies in the study were head and neck cancers, breast cancers and female genital cancers, and the incidence of anemia in these malignancies was higher than in other tumors. When sub-classified a higher prevalence in gynecological tumors was noted. The majority of anemic patients had mild anemia, with microcytic hypochromic anemia being the most common type. Conclusions: The study provides valuable information on the incidence and severity of anemia in patients with non-luminal solid tumors, which can help clinicians in their treatment planning and management.

Evaluation of PAM50 intrinsic subtypes and risk of recurrence (ROR) scores in premenopausal women with early-stage HR+ breast cancer: A secondary analysis of the SOFT trial.

504 Background: The landmark Suppression of Ovarian Function Trial (SOFT) in premenopausal breast cancer patients revealed that the addition of ovarian function suppression (OFS) to adjuvant endocrine therapy with either tamoxifen (T+OFS) or exemestane (E+OFS) reduces the risk of recurrence compared with adjuvant tamoxifen alone. There are no biomarkers to aid decision-making about intensification of endocrine therapy with OFS. The purpose of this study is to assess the prognostic and predictive ability of PAM50 intrinsic subtypes and ROR scores in premenopausal women with HR+/HER2- breast cancer in the SOFT trial. Methods: Gene expression analyses were performed via the NanoString Breast Cancer 360 assay on RNA isolated from FFPE tumor samples from the SOFT trial that were HR+/HER2- (n=1245/3047). PAM50 subtype and ROR score were determined centrally by NanoString Technologies (Seattle, WA, USA), blinded to clinical characteristics, treatment and outcome. Median follow-up was 12 years. Primary endpoint in this study was distant recurrence-free interval (DRFI). Secondary endpoints were breast cancer-free interval (BCFI) and disease-free survival (DFS). Kaplan-Meier analysis and Cox proportional hazards regression models, stratified by prior chemotherapy and lymph node status, were used to evaluate the predictive performance of PAM50 intrinsic subtypes and ROR categories (low vs intermediate vs high), and secondarily ROR score as a continuous variable. We also investigated differences between very young (&lt;40yrs) vs young (&gt;40yrs) women. Results: Tumor samples from 1084/1245 (87%) patients successfully completed PAM50 testing and are included in this analysis. Patient characteristics in this cohort were similar to the entire SOFT trial population. Intrinsic subtype and ROR category distribution is described below. Subtype distribution significantly differed between very young vs young premenopausal women, with fewer luminal A and more luminal B and non-luminal tumors seen in the very young (p&lt;0.001). The ROR score distribution also differed significantly: in node-negative patients there were significantly more ROR-high scores amongst very young compared to young women (36% vs 14%, p&lt;0.001). Conclusion: Breast cancer diagnosed in very young women has aggressive disease biology. Prognostic and predictive analyses of both intrinsic subtypes and the ROR score are ongoing and will be presented at the meeting. Clinical trial information: NCT00066690 . [Table: see text]

Preoperative considerations and benefits of neoadjuvant chemotherapy: insights from a 12-year review of the Hong Kong Breast Cancer Registry.

Neoadjuvant chemotherapy (NAC) was initially used for locally advanced or inoperable breast cancers. Its extension to early disease has facilitated breast-conserving surgery (BCS). This study investigated the use of NAC in patients registered with the Hong Kong Breast Cancer Registry (HKBCR); it also assessed NAC effectiveness according to rates of pathological complete response (pCR) and BCS. Records were retrieved from the HKBCR regarding 13 435 women who had been diagnosed with invasive breast cancer during the period of 2006 to 2017, including 1084 patients who received NAC. The proportion of patients treated with NAC nearly doubled from 5.6% in 2006-2011 to 10.3% in 2012-2017. The increase was most pronounced among patients with stage II or III disease. In terms of biological subtype, substantial increases in the receipt of NAC were evident among patients with triple-negative and human epidermal growth factor receptor 2 (HER2)-positive (non-luminal) tumours. The best rates of pCR were observed in patients with HER2-positive (non-luminal) [46.0%] tumours, followed by patients with luminal B (HER2-positive) [29.4%] and triple-negative (29.3%) tumours. After NAC, the rate of BCS was 53.9% in patients with clinical stage IIA disease, compared with 38.2% in patients with pathological stage IIA disease who did not receive NAC. The use of NAC in Hong Kong increased from 2006 to 2017. The findings regarding rates of pCR and BCS indicate that NAC is an effective treatment; it should be considered in patients with stage ≥II disease, as well as patients with HER2- positive (non-luminal) or triple-negative breast cancers.

Abstract PD10-07: PD10-07 Low plasma estradiol, low expression of estrogen responsive genes and TP53 mutations are associated with poor anti-proliferative response to aromatase inhibitors

Abstract Background: Aromatase inhibitors (AIs) are highly effective at reducing recurrences and mortality in postmenopausal patients with estrogen receptor positive breast cancer (ER+ BC). Poor anti-proliferative (Ki67) response or ER+ BCs to AIs after 2 weeks is associated with worse long-term outcomes. Factors that relate to the degree of the response may identify markers and/or mechansims of resistance. Methods: The PeriOperative Endocrine Therapy for Individualizing Care (POETIC) trial randomized 4,480 with ER+ BC to 2 weeks’ AI before surgery or no presurgical treatment. All patients within the bottom 15% of Ki67 responders to AI (poor responders [PRs]; n=177 with RNA extracted) were selected from and matched to good responders (GRs) within the 50% showing the best response (n=190). Matching was based on baseline Ki67 levels as measured by immunohistochemistry (IHC). Response to AI was measured by the percentage change in Ki67 after 2 weeks’ treatment. PRs were further divided into groups expressing high ESR1 (PRs ESR1HIGH; n=119) and low ESR1 (PRs ESR1LOW; n=58) levels since there were very few GRs with low ESR1. RNAseq, targeted exome DNA sequencing of 87 BC/resistance related genes and measurement of plasma estradiol levels by mass spectrometry were performed to understand mechanisms of de novo resistance. Intrinsic subtypes were estimated from RNAseq data. Results: More than 90% of PRs ESR1LOW were non-luminal subtypes with low expression of estrogen-responsive genes. In contrast, 11% of PRs ESR1HIGH were non-luminal compared to 4% of GRs but only HER2-enriched subtypes were significantly higher in PR ESR1HIGH (p=0.05, Fisher exact). While AI treatment had limited impact on Ki67 IHC values in PRs ESR1HIGH, PGR expression was more than 2-fold lower after 2 weeks of AI. Gene-set enrichment analysis showed significantly lower expression of estrogen-response genes in PRs ESR1HIGH compared to GRs (FDR&amp;lt; 10-9) at baseline despite similar percentage of Luminal subtypes in PRs ESR1HIGH and GRs. Plasma estradiol levels were correlated with expression of estrogen-response genes (FDR=0.01) and levels were significantly lower in PRs ESR1HIGH compared to GRs (p=0.003, Mann Whitney). PRs ESR1HIGH had significantly more mutations in RB1, TP53, ARID1B and DNAH11 genes (p&amp;lt; 0.05, Fisher exact). TP53 mutations were significantly enriched in Luminal-A PRs ESR1HIGH compared to GRs (22% and 3% respectively; p=0.003, Fisher exact), but not in Luminal-B tumors (23% and 15% mutated respectively). Discussion and conclusions: In approximately 33% of PRs, de novo AI resistance was associated with and most likely due to low expression of ER/ESR1 and estrogen-responsive genes in non-luminal tumors. In the remaining tumors, AI treatment still impacted some estrogen responsive genes but had limited downstream impact on suppressing proliferation. This might be due to mutations including in TP53 that limit suppression of proliferation downstream of estrogen signaling. The proportion of Luminal tumors in GRs and PRs ESR1HIGH was similar, suggesting better outcome of Luminal-A tumors on AI is likely due to their better intrinsic prognosis rather than better response to endocrine therapy. Citation Format: Eugene F. Schuster, Elena López-Knowles, Anastasia Alataki, Lila Zabaglo, Elizabeth Folkerd, David Evans, Kally Sidhu, Holly Tovey, Perry Maxwell, Nicholas Turner, Stephen Johnston, Manuel Salto-Tellez, Maggie Chon U Cheang, John Robertson, Ian Smith, Judith Bliss, Mitch Dowsett. PD10-07 Low plasma estradiol, low expression of estrogen responsive genes and TP53 mutations are associated with poor anti-proliferative response to aromatase inhibitors [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 PD10-07.

Abstract P1-04-10: Association of stromal tumor infiltrating lymphocytes (sTILs) in pretreatment biopsies in different molecular subtypes of HER2+/ER+ breast cancer: Assessment of NRG Oncology/NSABP B-52

Abstract Background: The primary aim of the NRG Oncology/NSABP B-52 clinical trial was to test if estrogen deprivation (ED) administered concomitantly with neoadjuvant docetaxel, carboplatin, trastuzumab, and pertuzumab (TCHP), would improve the pCR rate in patients with HER2+/ER+ early breast cancer. A numerical increase in the pCR rate was observed with ED (46.1% v 40.9%), but the difference was not statistically significant. The purposes of this study were to assess the association of sTILs in pretreatment biopsies with pCR in the total population and within the molecular subtypes of breast cancer and to assess changes in sTILs between pre- and on-treatment biopsies. The secondary endpoints of recurrence-free interval (RFI) and overall survival (OS) are currently being analyzed and will be presented along with association of these endpoints with sTILs in pretreatment biopsies in the total cohort and within molecular subtypes. Methods: Scoring of sTILs on routine H&amp;E slides from pre-treatment biopsies with sufficient tumor from 249 of the 315 patients (79%) entered in B-52 were performed by one of two pathologists (SKM, RSM). Both pathologists scored sTILs on a subset of 64 patients to document concordance. Wilcoxon two-sided test, box and whisker plots, and forest plots were used to assess associations with pCR. Molecular subtypes were determined utilizing RNA-seq data and AIMS subtyping method. On-treatment biopsies were available in 46 patients and were scored and compared to paired baseline samples. Results: Good concordance between pathologists was established with an inter-pathologist difference of ˂20% difference between scores in 92% of cases. sTILs in pre-treatment samples were associated with pCR across both arms of the trial (p=0.0074) and in the TCHP+ED arm (p=0.033), but not in the TCHP arm (p=0.093). The distribution of intrinsic subtypes was 34% luminal B, 29% luminal A, 28% HER2E, 5.8% normal, and 2.7% basal, with no significant differences between the arms. Presence of sTILs showed a trend for association with pCR in HER2E pre-treatment samples (p=0.054) but not in non-HER2E (p=0.75). Similarly, sTILs were associated with pCR in non-luminal tumors (p=0.055) but not in luminal tumors (p=0.44). Stratification by treatment arm and menopausal status suggested sTILs are associated with pCR in premenopausal women treated with TCHP (OR: 1.04, 95% CI=1.00-1.09). Interestingly, decreases in the sTIL scores with treatment were associated with pCR in the TCHP+ED arm (p=0.01) but not in the TCHP arm. Analysis of RFI and OS on B-52 is ongoing and will be presented along with associations of sTILs with intrinsic subtypes for RFI and OS. Conclusions: Although a positive correlation between sTILs and pCR was observed, the clinical utility appears limited because of the extensive overlap in the TIL scores between pCR and non-pCR tumors. Significance for a positive association of sTILs with pCR was detected in HER2E but not in luminal tumors. This may be due to the molecular differences of the subtypes, or the make-up of the TILs, or both. The association of a decrease in sTILs with TCHP+ED treatment needs further investigation. The small number of samples is a limitation of the study; however, the B-52 protocol specified that the collection of the B-52 samples was for the purpose of exploratory analysis. Our results highlight the molecular heterogeneity of the HER+/ER+ patient population and suggests that different treatment strategies may be required in future treatment regimens for this patient population. Support: NSABP Foundation; BCRF; 3U10CA180868-03S2, -180822; UG1CA189867; Genentech. Citation Format: Katherine L. Pogue-Geile, Sai K. Maley, Rim S. Kim, Ying Wang, Roberto Salgado, Corey Lipchik, Huichen Feng, Reena S. Cecchini, Samuel A. Jacobs, Ashok Srinivasan, Eleftherios (Terry) Mamounas, Charles E. Geyer Jr, Priya Rastogi, C. Kent Osborne, Soonmyung Paik, Norman Wolmark, Peter C. Lucas, Mothaffar Rimawi. Association of stromal tumor infiltrating lymphocytes (sTILs) in pretreatment biopsies in different molecular subtypes of HER2+/ER+ breast cancer: Assessment of NRG Oncology/NSABP B-52 [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 P1-04-10.

Abstract P4-02-13: Homologous recombination deficiency, RB-loss gene signatures, intrinsic subtype and response to neoadjuvant treatment in HR+/HER2- early breast cancer: a correlative analysis of two phase II trials

Abstract Background: Hormone-receptor (HR)+/HER2- breast cancer (BC) is a biologically heterogeneous disease. Homologous recombination deficiency (HRD) and BRCA mutations have been previously reported to be associated with worse outcomes in HR+/HER2- metastatic BC patients receiving CDK4/6 inhibitors and endocrine therapy. Here, we assess the relation between HRD and RB-loss signatures, intrinsic subtyping, the PAM50-based chemo-endocrine score, and response to chemotherapy-based therapy and endocrine treatment in HR+/HER2- early BC. Methods: GIADA is a multicentric neoadjuvant phase II trial that treated premenopausal patients with Luminal B (LumB)-like BC (HR-positive, HER2-negative, with Ki67&amp;gt;20% and/or histologic Grade 3) with a combination of chemotherapy, immunotherapy and endocrine treatment. Expression of 758 genes on baseline tumor samples from all 43 patients was quantified by nCounter platform. The LETLOB phase II trial randomized postmenopausal women with clinical stage II-IIIA HR+/HER2- BC to neoadjuvant letrozole + lapatinib or letrozole + placebo for 6 months (Guarneri, JCO 2014). Gene-expression data (Affymetrix platform) from pre-treatment frozen core-biopsies was available from 66 out of 92 pts enrolled. Intrinsic subtype was assigned using a research-based PAM50 subtype predictor. A published HRD signature (Peng, Nat Commun 2014) and a signature of RB loss (RBsig), previously reported to potentially predict resistance to CDK4/6 inhibitors in HR+/HER2- BC (Malorni, Oncotarget 2016) were computed. The PAM50 based chemo-endocrine score (CES) was calculated using published definition (Prat, CCR 2017). Higher values of CES indicate increased endocrine sensitivity, while lower values indicate chemosensitivity. Association between genomic signatures was assessed through Pearson’s correlation coefficient. Association of genomic signatures with pCR was assessed through logistic regression and association with PEPI scores was assessed through Kruskal-Wallis test. Results: HRD signature levels were significantly higher in non-luminal (Basal-like and HER2-enriched) tumors as compared to Luminal (A or B) tumors (p&amp;gt;0.001 in the GIADA trial, p=0.021 in the LETLOB trial). Moreover, higher levels of HRD signature were associated with higher levels of RB-loss signature (Pearson correlation 0.355, p=0.020 in the GIADA trial; Pearson correlation 0.942, p&amp;lt; 0.001 in the LETLOB trial), higher levels of Basal-like signature (Pearson correlation 0.502, p&amp;lt; 0.001 in the GIADA trial; Pearson correlation 0.373, p=0.002 in the LETLOB trial) and lower levels of CES (Pearson correlation -0.422, p=0.005 in the GIADA trial; Pearson correlation -0.763, p&amp;lt; 0.001 in the LETLOB trial), indicative of higher chemosensitivity. In the GIADA trial, higher levels of HRD signature (p=0.018) and RBloss signature (p=0.073) and lower levels of CES (p=0.007) were associated with higher pCR rates after chemo, endocrine and immunotherapy. In the LETLOB trial, lower levels of HRD signature (p=0.068) and RBloss signature (p=0.042) and higher levels of CES (p=0.050) were associated with higher sensitivity to endocrine treatment (lower PEPI scores, 0 vs 1-3 vs 4 or more, after neoadjuvant letrozole). Conclusions: In HR+/HER2- early BC, HRD gene signatures, RB-loss gene signatures and non-luminal (especially Basal-like) intrinsic subtyping are associated with each other and associated with higher sensitivity to chemotherapy-based therapy and lower sensitivity to endocrine treatment. These observations might help correctly tailor systemic therapy, including biologic agents, in patients with HR+/HER2- early and advanced BC. Citation Format: Gaia Griguolo, Federica Miglietta, Laia Paré, Daniele G. Generali, Antonio Frassoldati, Antonino Musolino, Simon Spazzapan, Grazia Vernaci, Tommaso Giarratano, Marcello Lo Mele, Giancarlo Bisagni, Federico Piacentini, Enrico Tagliafico, Katia Cagossi, Francesca Schiavi, Claudia Pinato, Aleix Prat, Valentina Guarneri, Maria Vittoria Dieci. Homologous recombination deficiency, RB-loss gene signatures, intrinsic subtype and response to neoadjuvant treatment in HR+/HER2- early breast cancer: a correlative analysis of two phase II trials [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 P4-02-13.

Abstract P3-06-02: TATEN TRIAL (SOLTI-1716) Targeting non-Luminal disease by PAM50 with pembrolizumab + paclitaxel in Hormone Receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC): interim analysis

Abstract Background Within HR+/HER2- disease, patients with non-luminal subtypes of breast cancer (HER2-enriched [HER2-E] and Basal-like) have poorer prognosis than those with luminal subtypes, may be more sensitive to chemotherapy, and have higher expression of immune-related genes and tumor infiltrating lymphocytes (TILs). Here, we report the interim efficacy and safety data of the TATEN trial (NCT04251169), the first study designed to evaluate pembrolizumab and paclitaxel in HR+/HER2-negative, PAM50 non-luminal, metastatic breast cancer (MBC). Methods TATEN is a single-arm, multicenter phase II study evaluating pembrolizumab in combination with paclitaxel in patients with HR+/HER2-, PAM50 non-luminal, MBC. Key inclusion criteria include progression to prior CDK4/6 inhibitors, presence of measurable disease by RECIST V1.1, no prior chemotherapy for MBC, and ECOG 0-1. Patients receive pembrolizumab at 200 mg every 3 weeks (on D1 of each 21-day cycle, beginning at cycle 1) in combination with weekly paclitaxel at 80 mg/m2, beginning at cycle 2. The primary endpoint is to evaluate overall response rate (ORR), defined as the rate of complete (CR) and partial response (PR) according to RECIST V1.1. Secondary endpoints include clinical benefit rate (CBR; CR + PR + stable disease &amp;gt;24 weeks), progression free survival, overall survival, safety, and predictive biomarkers. Tumor samples collected during advanced/metastatic disease are mandatory to assess PAM50 and other translational endpoints. This study had a planned interim analysis after 15 patients were evaluable for ORR based on a Simon’s two stage design with 80% power and a type I error rate of 0.05. Stage I of the trial would be considered successful if at least 6 patients achieved a PR and/or CR. In that case, the trial would recruit up to 46 evaluable patients for a target ORR ≥ 41. Here we report results from the patients who received at least one dose of combination treatment and had a first, post-baseline, tumor assessment according to RECIST v1.1 (evaluable population). Results From July 2020 to December 2021, 119 patients were screened, and 25 PAM50 non-luminal tumors were identified (21%). From these, 17 (68%) patients were recruited, and 15 were evaluable for primary endpoint. Two patients discontinued the trial before the first dose of pembrolizumab and paclitaxel, because of clinical progressive disease (PD). Baseline patient characteristics were as follows: median age 53 years (range: 40-77), ECOG 0 52.9%, de novo MBC at diagnosis 29.4%, and visceral disease 64.7% (including 53.3% with liver metastasis). Ten patients had received paclitaxel treatment in the adjuvant setting. Regarding PAM50 intrinsic subtype, two patients had basal-like and 13 HER2-E tumors. At the time of data cut-off (May 17,2022), 8 patients (53.3%) had stopped their treatment because of PD and 2 (13.3%) due to toxicity. Five patients (33.3%) were still on treatment. The ORR was 53.3 % (8 of 15, 95% CI 26.6-78.7), meeting the pre-specified ORR for the first stage of the trial. The CBR was 86.6% (13 of 15, 95%CI 59.5-98.34), and median PFS was 7.5 months (95% CI: 5.6 – 10.2). Overall, all patients experienced treatment-related adverse events (TRAEs) of any grade, while 53.3% of patients experienced grade 3 TRAEs. No grade 4 or 5 TRAEs were reported in the evaluable population. Correlative analysis including gene expression analysis and centralized TILs scoring and PD-L1 IHC will be presented. Conclusions The first stage of TATEN combining pembrolizumab with paclitaxel after progression to CDK4/6 inhibitors in patients with HR+/HER2-negative, PAM50 non-luminal MBC met its pre-specified endpoint. Completion of the stage II part of the trial with the inclusion of up to 46 patients is warranted to assess the activity of this combination in this group of patients. Correlative studies to find predictive biomarkers of response to this regimen are ongoing and will be presented at the meeting. This study was funded by MSD. Citation Format: Aleix Prat, Tomás Pascual, Montserrat Muñoz, Cristina Hernando, Silvia Vazquez, Salvador Blanch, Manuel Alva, Mafalda Oliveira, Esther Sanfeliu, Lorea Villanueva, Fara Brasó-Maristany, Nuria Chic, Eva Ciruelos. TATEN TRIAL (SOLTI-1716) Targeting non-Luminal disease by PAM50 with pembrolizumab + paclitaxel in Hormone Receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC): interim analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-06-02.