Abstract P2-26-17: Establishment of an in vitro preclinical platform: A living biobank of patient-derived organoids with ER+ breast cancer

Introduction and objectives Estrogen receptor positive (ER+) tumors are the most common form of breast cancer and are responsible for most of the deaths from the disease. Treatment of ER+ breast cancer comprises interventions that suppress estrogen production and/or target the ER directly. While endocrine therapy has considerably reduced recurrence and mortality from breast cancer, de novo and acquired resistance to this treatment remains a major challenge. In this context, patient-derived organoids (PDOs), 3D structures composed of epithelial cells, are changing our understanding of cancer heterogeneity and its implications for personalized medicine. Our aim was to establish and characterize a PDO platform of ER+ breast cancer as preclinical tool to decipher and target this heterogeneity in order to tailor effective treatments based on the precise molecular makeup of the tumor. Material and Methods Surgical resections were collected from patients diagnosed with ER+ breast cancer. Organoid generation from patient material were divided in three main steps: 1) mechanical fragmentation of tissue pieces; 2) digestion of fragments into single-cell suspension; and 3) plating of cell preparations into matrigel domes to mimic the extracellular matrix. Organoids were passaged every 7–21 days based on confluency. Each newly organoid line was cryopreserved for further expansion. Results We have successfully achieved an outgrowth efficiency of almost 50% for PDOs from patients diagnosed with breast cancer. Characterization of PDO cultures is essential to validate its predictive potential. To asses that PDOs represent the tumor of the patient, for each organoid line, expression levels of the main histological markers (ER, PR, HER2, Ki67) were evaluated and correlated with the tissue of origin. In parallel, we have performed immunofluorescence on paraffin-embedded organoid samples with routinely used cancer stem cell markers. Potential contamination with normal cells (present in the resection used to establish the culture) should be considered. To address the tumor purity of the culture we have performed targeted DNA sequencing in both the original tissue and established PDOs. Conclusions PDOs represent a superior preclinical system compared to previous models due to their inherent heterogeneity, long-term stability, applicability for high-throughput screens and enhanced capacity to capture tumor characteristics. Therefore, the implementation of a well-annotated patient-derived organoid biobank will be of great interest for drug discovery and personalized therapy. Understanding the sources and implications of tumor heterogeneity will undoubtedly improve our evolving definition of cancer and aid in the design of effective patient-specific treatment strategies.

Citation Format: Maria A Dominguez-Cejudo, Raquel Chapresto, Ana Gil-Torralvo, Francisco Javier Salvador Bofill, Sonia Molina-Pinelo. Establishment of an in vitro preclinical platform: A living biobank of patient-derived organoids with ER+ breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-26-17.

Abstract P4-07-29: Olaparib plus Trastuzumab in HER2[+] BRCA-Mutated Advanced Breast Cancer Patients: The OPHELIA Study

Background: Olaparib (O) is approved for the treatment of HER2[-] patients (pts) with early or metastatic breast cancer and a germline BRCA mutation. Nevertheless, there is no evidence that HER2[+] tumors are resistant to PARPi. Preclinical data support that HER2[+] cells are sensitive to PARPi and strongly suggest that PARP inhibition augments the efficacy of trastuzumab (T). To test whether PARPi is synergistic with anti-HER2 therapy, the OPHELIA study has assessed the efficacy and safety of O in combination with T in pts with HER2[+] germinal BRCA-mutated advanced breast cancer (ABC). Methods: OPHELIA (NCT03931551) is an open-label, multicenter, single-arm, phase II trial. The study enrolled pts aged ≥18 years diagnosed of HER2[+] ABC with germinal deleterious mutations in BRCA1 or BRCA2 who had received at least one prior systemic regimen for advanced disease (including a pertuzumab- or trastuzumab emtansine based regimen). Pts received O (300 mg oral, twice daily) plus T (either loading dose of 8 mg/kg IV infusion, and subsequent 3-weekly doses of 6 mg/kg IV infusion; or 600 mg SC injection, on day 1 of every 21-day cycle) until disease progression, unacceptable toxicity, or consent withdrawal. Primary endpoint was investigator-assessed clinical benefit rate (CBR) for at least 24 weeks as per RECIST v.1.1. Secondary endpoints included overall response rate (ORR), duration of response (DoR), progression-free survival (PFS), overall survival (OS); and safety and tolerability as per NCI-CTCAE v.5.0. The primary analysis evaluated CBR (H0: ≤5%; H1: ≥30%) based on exact binomial test. Sample size was designed to attain a 90% power at 10% one-sided alpha level. Results: From Mar 25, 2019, through Mar 2, 2022, 5 pts (from a total of 42 pts evaluated) were enrolled at 17 sites in Spain. Median age was 37.0 (range 32–54) years, 1 (20.0%) patient was male, 4 (80.0%) pts carried germinal BRCA2 mutations, 4 (80.0%) pts had received ≥ 3 advanced disease treatments lines, and 4 (80.0%) pts presented ≥ 2 metastatic sites. At data cutoff (Mar 2, 2022), with a median follow-up of 18.7 months (min: 11.7; max: 22.1), 40.0% of pts remained on therapy. CBR at 24 weeks was 80.0% meeting the primary endpoint (4 of 5 pts; 95% CI, 28.4% to 99.5%, p< 0.001). ORR (1 complete and 2 partial responses) was 60.0% (95% CI, 17.4% to 94.7%), and median DoR was 3.8 months (95% CI, 2.5 to 8.3 months). Two (40.0%) pts had PFS events due to disease progression at 5.2 and 1.2 months, respectively. Rest of pts were treated for 5.5, 11.2, and 19.0 months. There were 2 (40.0%) deaths at 14.0 and 18.5 months. The most common non-hematological treatment emergent adverse events (TEAEs) of any grade (G) were fatigue (60.0%; 0% G≥3), nausea (60.0%; 0% G≥3), vomiting (40.0%; 0% G≥3), and back pain (40.0%; 0% G≥3). Anemia (40.0%; 20.0% G≥3) and lymphopenia (40.0%; 20.0% G≥3) were the most frequent hematological TEAEs. One (20.0%) patient discontinued treatment because of a drug-related TEAE (leukopenia). A dose reduction of O was reported in 1 (20.0%) patient. No treatment-related deaths were reported. Conclusions: HER2 overexpression in germline BRCA-mutated ABC is infrequent. The activity observed in these 5 pts indicates that O+T combination might be of help in this group of pts. We strongly believe that randomized data are not needed, and RWE studies might help us to understand the real activity of this combination. Toxicity was as expected.

Citation Format: José E. Alés-Martínez, Judith Balmaña, Pedro Sánchez-Rovira, Francisco Javier Salvador Bofill, José Ángel García-Sáenz, Isabel Pimentel, Serafin Morales Murillo, Adela Fernández, Ainhara Lahuerta Martínez, Neus Ferrer, Pilar Zamora, Begoña Bermejo, Tamara Díaz-Redondo, María Helena Lopez-Ceballos, María Galán, Andrea Malfettone, Laura Calabuig, Miguel Sampayo-Cordero, José Manuel Pérez-García, Javier Cortés, Antonio Llombart-Cussac. Olaparib plus Trastuzumab in HER2[+] BRCA-Mutated Advanced Breast Cancer Patients: The OPHELIA Study [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 P4-07-29.

Abstract P5-02-31: Genetic determinants of response to patritumab deruxtecan (HER3-DXd) in hormone receptor-positive/HER2-negative (HR+/HER2-) breast cancer: a correlative analysis from SOLTI TOT-HER3 trial

Background: Baseline HER3 protein or ERBB3 mRNA levels do not seem to predict efficacy from HER3-DXd in early-stage and advanced HR+/HER2- breast cancer (Prat et al. ESMO Breast 2022; Krop et al. ASCO 2022). Here, we evaluated potential baseline pre-treatment genetic determinants of efficacy to HER3-DXd. Methods: SOLTI TOT-HER3 (NCT04610528) is a window of opportunity, multicenter, pre-operative trial which enrolled, in part A, 77 evaluable patients with untreated HR+/HER2- operable (≥1 cm) breast cancer. Patients received a single dose of HER3-DXd (6.4 mg/kg). The primary objective was to evaluate the CelTIL score variation between pre- and post-treatment (day 21) samples. CelTIL combines % of tumor cellularity and % of tumor-infiltrating lymphocytes into a single score. DNA and RNA were purified from pre-treatment baseline FFPE tumor samples. Gene expression was evaluated using a custom 67-gene panel on the nCounter. NGS-based DNA-seq was performed using the VHIO-300 panel, which estimates tumor mutational burden (TMB), identifies copy-number aberrations (CNAs) across the entire genome and calls mutational status of >300 genes. From CNA data, 150 previously defined DNA-based signatures (Xia et al. Nat Comm 2019) trained to capture RNA- and protein-based phenotypes such as the PAM50-related biology were evaluated. Associations of each variable with efficacy (i.e., CelTIL relative changes, and tumor cellularity relative changes) were adjusted for multiple-testing (false discovery rate [FDR] < 5%). The area under the ROC Curve (AUC) was used to estimate the discrimination performance of each variable. Results: RNA and DNA data were obtained from 45 (58%) patients. Baseline characteristics in this subset of patients were generally similar to the original TOT-HER3 population. Among 228 variables (single mutation status, single gene expression, PAM50 signatures, TMB, and DNA CNA-based signatures), 139 (61%) were found significantly associated (FDR< 5%) with CelTIL changes at day 21. Among them, TP53 mutations (n=7) were found associated with higher CelTIL response compared to TP53 wild type (71% [95% CI=-5.4-17.8] vs. 24% [95% CI=15.9-55.4], FDR=2.1%). In addition, RNA-based genes tracking Basal-related biology (e.g., CCNE1, AUC=0.71) or immune expression (e.g., PDCD1, AUC=0.73, or CD68, AUC=0.62), together with RNA/DNA-based signatures tracking proliferation and/or basal-related biology (e.g., retinoblastoma loss-of-heterozygozity [RB-LOH], AUC=0.76), were associated with high CelTIL response. Conversely, RNA/DNA-based signatures tracking endocrine sensitivity/Luminal A-related biology (e.g., Scorr_IE_Correlation, AUC=0.76) were associated with low/lack of CelTIL response. PIK3CA somatic mutations (n=14, 31% of cases), and TMB (range 2.2-12.7) were not found associated with CelTIL response. Similar overall results were obtained when relative changes in tumor cellularity (instead of CelTIL) was evaluated as the efficacy endpoint. Conclusions: TP53 mutations, immune-related genes, and DNA/RNA-based phenotypic signatures tracking Basal- or Luminal A-related biology such as the DNA-based RB-LOH score or the endocrine sensitivity score (Scorr_IE_Correlation) are associated with CelTIL changes in response to HER3-DXd in HR+/HER2- breast cancer. Further RNA- and DNA-based analyses will be evaluated.

Citation Format: Fara Brasó-Maristany, Claudette Falato, Olga Martínez-Sáez, Juan Miguel Cejalvo, Mireia Margelí, Pablo Tolosa, Francisco Javier Salvador Bofill, Josefina Cruz, Blanca González-Farré, Esther Sanfeliu, Míriam Arumí, Guillermo Villacampa, Eva Ciruelos, Martín Espinosa-Bravo, Yann Izarzuzaga, Patricia Galván, Judit Matito, Sonia Pernas, Anu Santhanagopal, Stephen Esker, Parul Patel, Pang-Dian Fan, Juan Manuel Ferrero-Cafiero, Ana Vivancos, Tomás Pascual, Aleix Prat, Mafalda Oliveira. Genetic determinants of response to patritumab deruxtecan (HER3-DXd) in hormone receptor-positive/HER2-negative (HR+/HER2-) breast cancer: a correlative analysis from SOLTI TOT-HER3 trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-31.

Abstract P1-04-18: Identification of UGT2B family genes as potential biomarkers of response to neoadjuvant therapy in HER2+ breast cancer

INTRODUCTION Human Epidermal Growth Factor Receptor (HER2) is overexpressed and/or amplified in 15-20% of breast cancer at time of first diagnosis and is associated with an aggressive clinical progression disease. Management of HER2+ early breast cancer, include a combination of sequential chemotherapy and HER2-targeted therapy, which is currently the gold standard of care. Achieving pathological complete response (pCR) to after neoadjuvant therapy has been proposed as a prognostic marker for the prediction of disease-free survival (DFS). Although there are different criteria to define pCR, in general pathological complete response is the absence of residual disease in breast and lymph nodes in the pathology analysis of the surgical piece resection (ypTo/is ypN0). However, there is a compelling need to identify molecular biomarkers that will help determine which patients will benefit from neoadjuvant therapy. Considering that the UGT2B family plays an important role in drug metabolism, our aim is to analyze its role as potential predictive biomarkers of pCR to neoadjuvant therapy in breast cancer. METHODS We included 18 female patients diagnosed as early breast cancer HER2+ at the time of neoadjuvant treatment. Tissue samples were obtained from the surgical resection performed at Virgen del Rocio Hospital (Seville, Spain) and were formalin-fixed paraffin-embedded (FFPE) to subsequently carry out the pertinent analyses of the study. All patients were treated with chemotherapy plus anti-HER2-targeted therapy and were stratified according to response to neoadjuvant treatment. We defined two groups: responder (R; RCB-0; n=14) and non-responder (NR; RCB-II/III; n=4). Total RNA from FFPE tissue was extracted using the RecoverAll Total Nucleic Acid Isolation commercial kit (Ambion, Austin, TX, USA) following the manufacturer’s instructions. RNA concentration was measured using the NanoDrop ND-1000 spectrophotometer (Nanodrop Tech, DE, USA). A total of 18 samples were labeled and hybridized with a Clariom D pico Array microarray (Affymetrix, Santa Clara, CA, USA) following the manufacturer’s instructions. Differences in expressed genes according to response were identified using the Mann–Whitney U test where p -values. < 0.05 were considered significant and ROC curve was used to determine predictor value of complete response for each member of UGT2 family. Differential expression between the two groups was analyzed using the statistical packages SPSS version 28 and R 4.1.1.1. Statistical significance was established for p-values ​​< 0.05 and fold change ≥ 2 RESULTS We found 954 differentially expressed transcripts: 311 downregulated transcripts (lower expression in R) and 643 upregulated transcripts (higher expression in R). Our data showed a significant upregulation in 5 genes of the UGT2B family in non-responder patients (p-value< 0.05). 3 genes of the UGT2b family showed an acceptable ability to discriminate responders and non-responders to neoadjuvant treatment of HER2-positive in the ROC (receiver operating characteristic curve) analysis. CONCLUSIONS We identified a set of transcript differentially expressed (FC>2; adjusted p-value< 0.05) in patients with residual disease (nR) when compared with tissue samples in patients that achieve pCR (R). UGT2B family genes are consistently upregulated in non-responder patients. UGT2B genes encode enzymes involved in glucuronidation. They are phase II drug-metabolizing enzymes with steroids removal capabilities in the liver and various steroid target tissues. An increased rate of glucuronidation is been associated with a loss of potency for the target drugs. These genes would be used as predictive biomarkers of pCR to neoadjuvant therapy in breast cancer.

Citation Format: Ana Gil-Torralvo, Marta Benavent, Maria A Dominguez-Cejudo, Alejandro Falcon, Mónica Cejuela, Begoña Vieites, Sonia Molina-Pinelo, Manuel Ruiz Borrego, Juan de la Haba-Rodríguez, Maria I Queipo, Francisco Javier Salvador Bofill. Identification of UGT2B family genes as potential biomarkers of response to neoadjuvant therapy in HER2+ breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-04-18.

Abstract P3-01-13: Palbociclib, ribociclib and abemaciclib in real-world data: risk of disease progression on first-line treatment of metastatic breast cancer

Introduction and objectives: Cyclin dependent kinase (CDK) 4/6 inhibitors along with endocrine therapy (ET) is the standard first-line for endocrine receptor (ER)-positive HER2-negative metastatic breast cancer. Three CDK 4/6 inhibitors have the FDA and EMA approval: abemaciclib, palbociclib and ribociclib. They appear to have notable differences in their pharmacokinetic characteristics and ability to inhibit every cyclin. Nevertheless, the natural history of disease associated with each CDK 4/6 inhibitor remains unclear. The aim of this study is to establish a risk prediction model for disease progression under the different therapeutic regimes and assess whether there are differences in terms of efficacy between them.

Methods: This is a retrospective observational study in which patients treated with ET plus abemaciclib, palbociclib or ribociclib as front line for metastatic breast cancer in Virgen del Rocio Hospital between April 2014 and April 2021 were selected. Patients in this population were followed for a period of 36 months. They were studied according to their clinical characteristics and disease outcome using descriptive analysis. The risk of progression was studied by a transversal method using a univariate logistic regression model. Moreover, Kaplan Meier curves were used to estimate progression-free survival (PFS) and the Breslow test to estimate the p value. All statistical analyses were performed with SPSS 28.0 (Statistical Package for the Social Sciences).

Results: A total of 189 patients were selected. 55(29.1%) of them received abemaciclib, 83(44%) palbociclib and 51(27%) ribociclib. 50(27%) patients had de novo metastatic disease, while 139(73%) were recurrences of previous disease. Almost half of the patients (45%) received fulvestrant and 104 (55%) patients received aromatase inhibitors. Table 1 represents the proportion of patients with visceral involvement and endocrine resistance in each arm. The univariate logistic regression model showed that patients treated with palbociclib had 2.36(CI95% 1.165-4.765) times the risk of progression compared to abemaciclib, while patients treated with ribociclib had 2.50(CI95% 1.139-5. 475) times the risk of progression compared to abemaciclib. Overall PFS was 30.03 months. A tendency towards best PFS with abemaciclib in comparison with the other CDK 4/6 inhibitors was appreciated, but it did not reach statistical significance (abemaciclib-palbociclib p=0.289; abemaciclib-ribociclib; p= 0.293; palbociclib-ribociclib p=0.979).

Conclusions: In our sample of patients with ER-positive HER2-negative metastatic breast cancer treated with the different CDK 4/6 inhibitors as front line therapy, patients with abemaciclib achieved a lower risk of progression and a trend toward longer PFS. Further follow-up will be necessary to determine whether abemaciclib provides greater benefit in PFS.

Table 1. Proportion of patients with visceral involvement and endocrine resistance in each arm. Visceral metastases: Liver, Lung, central nervous System; Non-Visceral: Bone, skin, Lymph node.

Citation Format: Mónica Cejuela, M. ángeles Castilla, Marta Benavent, Sonia Molina-Pinelo, Maria A Dominguez-Cejudo, Ana Gil, Alejandro Falcon, Francisco Javier Salvador Bofill. Palbociclib, ribociclib and abemaciclib in real-world data: risk of disease progression on first-line treatment of metastatic breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-01-13.

Assessment of Prognostic and Therapeutic Factors in Male Breast Cancer: An Observational Study of a Southwest Spanish Single Center

Background: Male breast cancer (MBC) accounts for less than 1% of breast cancer, requiring extrapolation of results from studies in women. The aim of the study is to evaluate prognostic and therapeutic factors with special focus in endocrine treatment (ET) on the disease outcome.Methods: Observational, retrospective, single-center study of 53 MBC treated between January 1997 and December 2018 participated in the study. Among the participants, 48 patients had a performance status (PS) 0-1 (91%), 48 were hormone-receptor-positive (91%) and 4 were human epidermal growth factor 2 receptor (HER2) positive (8%). A total of 45 patients (85%) were treated with ET, with 36 patients (68%) receiving treatment in an adjuvant setting. The association analysis was performed using Chi-square test and survival was estimated using Kaplan-Meier with SPSS v25. Results: The cohort had a median age of 68 years old (range: 40-88). We found that 84% had a non-metastatic breast cancer. A breast cancer gene (BRCA) analysis was carried out in 43% of the patients, showing BRCA2 mutated in 26.1% of those analyzed, without obtaining a benefit in overall survival (P=0.698). The analysis showed higher 5-year overall survival (OS) for PS 0 (P=0.010), absence of vascular invasion (P=0.033), Ki67 ?14% (P=0.041) and absence of metastasis at diagnosis (p<0.0001). Patients receiving adjuvant ET above 5 years had a longer median OS (89 vs 69.6 months, P=0.024), disease-free survival (DFS), and distant relapse (84 vs 48 months; P=0.005, and P=0.002, respectively).Conclusions: Several prognostic factors for male breast cancer have been described. Noteworthy, patients receiving adjuvant ET above 5 years had a higher OS and DFS. BRCA did not show prognostic value in OS in this cohort. Further studies with larger sample size are necessary.

Cross-sectional observational study to describe the clinicopathological and biological characteristics and the management of patients with HER2+ metastatic breast cancer who experienced complete or partial remission or disease stabilization during at least 3 years: LongHer study

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Background: Trastuzumab has shown an improvement in survival outcomes among patients with HER2+ metastatic breast cancer (MBC). Identification of factors and tumor molecular profiles that may predict long-term remission has become a key-issue. Methods: Multicenter, observational, cross-sectional study. Data were collected from women with HER2+ MBC treated with a trastuzumab-based regimen that experienced CR, PR or SD during at least 3 years. FFPE samples(at least 70% tumor cells)for Microarray Analysis were obtained. L2 Boosting for classification with classical Akaike Information criterion based on the binomial log-likelihood for stopping the boosting iterations algorithm was applied to RNA expression data, to identify variables related to clinical information. Predictive models of long term response were built using a Binary Logistic Regression with the Fisher's scoring. Results: 103 patients.Median age: 58(51-68) years. Metastatic disease diagnosed after a median of 24.7(1.8-51.9) months since primary diagnosis. Predominant type: ductal carcinoma(91.9%) and 59% histological grade III. Hormonal status: Progesterone receptor positive 39.2% and estrogen receptor positive 41.2%. Most common metastatic sites: multiple locations(31.4%), lung(23.5%), bone(14.7%) and liver(13.7%). Overexpression of HER2 assessed by IHC in 98.1% of patients, 91.1% were HER2+(3+) and 18.4% had FISH+ HER2 status. Tumor was positive for p53 (>30%) and Ki67(>20%) in 47.3% and 73.6%. Surgery: 87.4% of patients, 77.5% radical mastectomy. Surgery of metastases was performed on 16.8%. Trastuzumab used in combination in 88.3% with a median number of cycles of 35.5(7.0-46). 68.9% of patients achieved a CR, 20.4% PR and 10.7% had SD, during an overall median time of 55 (43-79) months. 4 patients discontinued trastuzumab due to toxicity. Conclusions: Trastuzumab may provide a substantial long-term survival benefit with a manageable safety profile in these patients. Molecular analysis will be presented in the forthcoming Congress.