Metastatic HER2 Research Articles

Abstract 6799: A porous silicon particle based particulate anti-cancer vaccine for immunotherapy

Abstract Background: Anti-cancer vaccine is a widely-studied strategy that activates innate and adaptive host immunity via its adjuvant components and tumor antigens against cancer. Unfortunately, its response rate in clinical trials was not promising. On the vaccine part, sufficient stimulation of strong and long-lasting local and systemic immunity and efficient promotion of intratumoral infiltration of cytotoxic T lymphocytes are among the critical issues determining the therapeutic efficacy of cancer vaccines in addition to the innate features of tumor. Our project aims to develop a porous silicon particle based particulate vaccine against cancer, and investigate the therapeutic mechanism and combinational effects with current first-line strategies. Method: We first screened the combinations of ligands of Toll-like receptors (TLRs) expressing on antigen presenting cells (APCs) and selected the most powerful combo for immune stimulation. We then loaded the identified adjuvants in addition to antigen peptides to produce vaccine particles. Stimulation and licensing of APCs were tested in vitro, and its therapeutic efficacies were evaluated on multiple orthotopic and systemic metastasis cancer murine models of breast and colon cancers. Furthermore, we investigated the vaccine’s synergistic effects and impacts on tumor microenviroment (TME) with an immunogenic chemotherapeutic oxaliplatin on a CT26 colon cancer model. Result: According to the adjuvant screening assays, we identified a capable combination of CpG1826 (CpG) and 2’3’-cGAMP (cGAMP), which extensively stimulated the activation, maturation and type-I interferon secretion of APCs. A µGCVax formulation composed by these two adjuvants and antigen peptides was then applied on primary and metastatic HER2+ breast cancer TUBO bearing mice. µGCVax potently promoted the activation and lymph node migration of CD8+ and CD103+ dendritic cells in vivo. Distal metastatic tumor nodules in all different tissues vanished after two vaccinations. Functional cure of cancer and extension of animal survival were achieved. Moreover, oxaliplatin treatment on colon cancer caused immunogenic cell death and generated an immune favorable TME in a subcutaneous CT26 colon cancer model. The combination of µGCVax with the oxaliplatin effectively blocked the progression of large tumor mass. We finally revealed that the reprogramming of TME and the promotion of efficacy were mostly achieved from diminishing myeloid-derived suppressor cells (MDSCs) in tumor. Conclusion: µGCVax is an effective and board-spectrum formulation for cancer immunotherapy. It effectively induces APC activation and licensing, and stimulates the innate and adaptive immunity against multiple cancers. The combination with oxaliplatin further promotes the therapeutic efficacy of µGCVax by decreasing tumor MDSCs. Citation Format: Junhua Mai, Yongbin Liu, Dongfang Yu, Haifa Shen. A porous silicon particle based particulate anti-cancer vaccine for immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6799.

Abstract 5060: Tucatinib does not alter oxaliplatin PK or associated renal function: An OCT2 and MATE transport inhibition study

Abstract Background: Oxaliplatin (OX)-containing regimens are frequently utilized to treat gastrointestinal (GI) cancers. OX is eliminated predominately via urinary excretion (GFR and active tubular secretion). The contribution of active transport via OCT2 and MATE1/2-K to OX clearance is not fully understood. Tyrosine kinase inhibitors (TKIs) are frequently found to interact with OCT2/MATE transporters; however, a gap in knowledge remains between their clinical potential to impact OX pharmacokinetics (PK) and in turn, impact renal function. Tucatinib (TUC) is a highly selective human epidermal growth factor receptor 2 (HER2)-directed TKI approved in multiple regions in combination with trastuzumab and capecitabine for adult patients with metastatic HER2+ breast cancer and is currently being investigated in other HER2+ tumors. TUC inhibits OCT2/MATE-mediated transport of metformin and creatinine in vitro and in vivo. In this study, we investigated the impact of TUC on OX plasma PK, OX renal clearance (Clr), and renal function. Methods: In vitro inhibition of OCT2/MATE-mediated transport of OX by TUC was assessed in OCT2, MATE1, or MATE2-K-expressing MDCK-II cells. SGNTUC-024 (NCT04430738) is a Ph1b/2 clinical study in patients with HER2+ GI cancers evaluating the impact of TUC on the safety and PK of OX. Patients received TUC 150 mg (Cohort 1A) or 300 mg (Cohort 1B) BID starting on C1D8 of a 2-week cycle in combination with modified FOLFOX6/7. Intensive PK was collected in plasma and urine for OX alone (C1D1) or with steady-state TUC (C2D1). Total plasma platinum (Pt, analyzed as a surrogate for OX and catabolites), plasma Pt ultrafiltrate (PUF, unbound), and urine Pt were quantitatively analyzed via ICP-MS. Serum Cystatin C (CysC) was measured as a pharmacodynamic (PD) renal function marker in Cohorts 1A and 1B. Results: TUC inhibited in vitro OX transport by MATE1 (IC50 = 0.0639 µM), MATE2-K (IC50 = 0.0382 µM), and OCT2 (IC50 = 0.491 µM). In 11 patients, total Pt and PUF AUC0-8h geometric mean ratio (GMR) and 90% confidence intervals (CI) between patients who received OX alone compared to in combination were 1.1 (0.98, 1.3) and 1.0 (0.78, 1.4) in Cohort 1A (n=4) and 1.1 (0.96, 1.2) and 1.0 (0.98, 1.1) in Cohort 1B (n=7), respectively. OX GM (%CV) renal clearance (Clr,0-8h in mL/min) and fraction excreted 24h post-dose (fe,0-24h) were similar with and without TUC in both Cohort 1A (C1D1 Clr0-8h = 277 (33), fe,0-24h = 22% (17); C2D1 Clr0-8h = 249 (78), fe,0-24h = 21% (15)) and Cohort 1B (C1D1 Clr0-8h = 189 (37), fe,0-24h = 17.7% (16); C2D1 Clr0-8h = 177 (40), fe,0-24h = 16.6% (35)). Reversible slight increases in CysC (normalized to baseline) on day 3 of each cycle, irrespective of tucatinib, were observed. Conclusions: This investigation of in vitro and in vivo determinants of OX PK demonstrates that TUC does not alter the renal clearance of oxaliplatin nor renal function when OX is administered in combination with TUC. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, Vineet Kumar, Michelle Ubowski, JoAl G. Mayor, Layth I. Abdulrasool, Clark M. Henderson, Joseph A. Ware, Christopher J. Endres. Tucatinib does not alter oxaliplatin PK or associated renal function: An OCT2 and MATE transport inhibition study. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5060.

Abstract 3990: Imaging molecular alterations during tucatinib response in preclinical models of HER2+ breast cancer

Abstract Introduction: Human epidermal growth factor receptor 2 (HER2) is overexpressed in 25% of breast cancers. Tucatinib, a small molecule HER2 inhibitor, was FDA approved for inoperable or metastatic HER2+ breast cancer. As many of these patients have inoperable tumors, there is a need to identify imaging metrics that can characterize response to tucatinib. Positron emission tomography (PET) imaging can quantify changes in the tumor microenvironment that precede changes in tumor size through imaging with radiopharmaceuticals that target proliferation (fluorothymidine, [18F]-FLT), hypoxia (fluoromisonidazole, [18F]-FMISO) and HER2 expression ([89Zr]-Pertuzumab). The goal of this study is to use advanced PET imaging to non-invasively monitor response to tucatinib in HER2+ primary breast cancer and quantify the subsequent tumor microenvironment modulation. Methods: HER2+ cell line (BT474) and patient derived xenograft (BCM 3472) tumor models were engrafted and developed to 270 ± 166.4 mm3 before being enrolled into experiments. Mice were treated with 50 mg/kg tucatinib via PO and were imaged with [18F]-FLT PET (N = 8) on days 0, 3 and 7, [18F]-FMISO PET (N = 6) on days 0, 3 and 7, or [89Zr]-Pertuzumab PET (N = 5) on days 0 and 14. Intratumoral proliferation, hypoxia and HER2 expression were quantified with standardized uptake value (SUV). Following the final imaging timepoint, tumors were excised for immunohistochemistry against Ki-67 (proliferation), pimonidazole (hypoxia), and HER2. A non-parametric T-test was used to assess for significance. Results: Tucatinib treated BT474 and BCM3472 tumors had a 2.07 and 2.63 fold decrease in tumor volume, respectively (p<0.01). Tucatinib treated BT474 and BCM3472 tumors had significantly decreased hypoxia and proliferation, relative to control tumors (p<0.05). Tucatinib treated BT474 tumors had significantly decreased HER2 expression (p<0.05); however, no significant change in HER2 expression was observed in tucatinib treated BCM3472 tumors. Conclusion: Tucatinib significantly decreases tumor volume and decreases intratumoral proliferation and hypoxia in both cell-line and patient-derived xenograft models of HER2+ breast cancer. Our data suggests molecular imaging may drive understanding of and predict response to tucatinib therapy. Acknowledgements: Tucatinib was provided by Seagen Inc. Bothell, Washington, USA. Citation Format: Patrick Song, Ameer Mansur, Anna Sorace. Imaging molecular alterations during tucatinib response in preclinical models of HER2+ breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3990.

Abstract 2622: Targeting Rac/Cdc42 GTPases to overcome HER2-targeted therapy resistance

Abstract Breast cancer is the most common cancer in women. Breast cancer is categorized by the overexpression (or lack thereof) of estrogen receptors (ER+/-), progesterone receptors (PR+/-) or human epidermal growth factor 2 receptors (HER2+/-). Specifically, HER2+ breast cancer is one of the most aggressive subtypes, comprising ~20% of all cases. Overexpression of the HER2 receptor leads to active downstream signaling that results in cell proliferation and metastasis. Clinically, this problem has been tackled by targeting the HER2 receptor with antibodies (e.g., Trastuzumab, Pertuzumab) and (or) tyrosine kinase inhibitors (TKIs; e.g., Lapatinib). However, patients may present with intrinsic or acquired resistance to these therapies. Molecular mechanisms of resistance to HER2 targeted therapy include activating mutations, alterations in downstream effectors, and compensation from other growth factor receptors. The active signaling sequelae from such mechanisms converge on the activation of guanine nucleotide exchange factors (GEFs) that regulate the GTPases Rac and Cdc42. These GTPases are critical for cell migration/invasion and have been correlated with poor prognosis in breast cancer patients. Therefore, targeting the activation of Rac/Cdc42 is a rational strategy to overcome HER2-targeted therapy resistance. Previously, we characterized the dual Rac/Cdc42 inhibitor MBQ-167 with IC50s of 103nM and 78nM for Rac and Cdc42, respectively. Our objective is to test MBQ-167 as an alternative to overcome HER2-targeted therapy resistance. To test the hypothesis that MBQ-167 will overcome HER2 therapy resistance, metastatic trastuzumab resistant HER2 overexpressing cells were treated with vehicle or individual or combined Trastuzumab and MBQ-167. Rac activity was determined by pulldown assays for active (GTP-bound) Rac, and viability was tested by MTT assays. Additionally, we measured apoptosis via caspase 3/7 activity and western blotted for the active signaling sequelae downstream of Rac. MBQ-167 reduced Rac activity and downstream signaling, as well as cell viability with a GI50 of 78nM after 72 hours, while caspase activity was increased after 24 hours of treatment. The results presented herein show the utility of the Rac/Cdc42 inhibitor MBQ-167 in overcoming HER2-targeted therapy resistance. Citation Format: Miciely Cristal Aponte Reyes, Luis E. Velazquez Vega, Suranganie Dharmawardhane. Targeting Rac/Cdc42 GTPases to overcome HER2-targeted therapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2622.

Abstract 3900: In vivo inhibition of metastatic HER2 positive trastuzumab resistant breast cancer using engineered destabilized 3UTR ARE of HER2 improves survival outcomes

Abstract Breast cancer is the most common form of cancer in women with mortality of about 58% in developing countries. HER2+ breast cancers are treated with trastuzumab in various forms in combination with chemotherapy and has been successful in targeting HER2 overexpression in HER2+ breast cancer and improving survival as a standard first line therapy for more than a decade. However, about 25% of early and 75% of late stage HER2 driven breast cancers are resistant to trastuzumab. For these patients, the clinical outcomes are grim. We report the destabilization of HER2 3‘UTR ARE which degraded oncogene HER2 transcript, protein expression, HER2 dependent kinases and interactome. In vitro, we transfected the engineered destabilizing HER2 constructs into BT474 clone 5 trastuzumab resistant breast cancer and within days, we inhibited cancer cell growth and degraded HER2 transcript and protein. The degradation of HER2 leads to loss of many kinases especially YES1 and WNK1 that are known causes of chemoresistance in HER2 positive trastuzumab resistant breast cancer. In vivo, we administered the destabilizing constructs as naked constructs or as complexed with nanocages to mice bearing tumors of BT474 clone 5 trastuzumab resistant cells. We found that our constructs, both the naked and nanocage-delivered, conferred significant survival (p values: 0.0178 and 0.00492) to about 60% of the exceptionally surviving mice compared to the controls. Taken together, we have developed a new therapy to target trastuzumab resistant HER2+ metastatic breast cancers with increased survival outcomes. Citation Format: Chidiebere U. Awah, Joo Sun Mun, Baris Boylu, Alooka Paragodaarachchi, Chika Ochu, Hiroshi Matsui, Olorunseun O. Ogunwobi. In vivo inhibition of metastatic HER2 positive trastuzumab resistant breast cancer using engineered destabilized 3UTR ARE of HER2 improves survival outcomes. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3900.

Abstract 4019: Preclinical activity of ELVN-002: A potent, selective, and irreversible HER2 and pan-HER2 mutant small molecule inhibitor for the treatment of HER2 driven malignancies

Abstract Mutation or amplification of the human epidermal growth factor receptor 2 (HER2) gene has been identified in numerous solid tumor types, including non-small cell lung cancer (NSCLC), breast, and colorectal cancer. These genetic alterations are believed to confer elevated HER2 activity resulting in oncogenic transformation. In NSCLC, an estimated 3% of patients harbor activating mutations in the HER2 gene. Enhertu (T-DXd), a HER2-specific antibody-drug conjugate was recently approved as an important therapy for this patient population. However, for patients who are not candidates for T-DXd or have discontinued treatment due to an adverse event or disease progression, there exist few therapeutic options. Accordingly, HER2 inhibitors have the potential to provide meaningful therapeutic benefit to these patients. Due to significant structural homology between EGFR and HER2, most investigational small molecule HER2 kinase inhibitors are dual EGFR/HER2 inhibitors and are substantially dose-limited by EGFR-related toxicities in patients. These toxicities likely limit their clinical activity. Currently, tucatinib is the only HER2-selective small molecule inhibitor approved for metastatic breast cancer in combination with trastuzumab and capecitabine. However, it lacks sufficient potency against several of the key clinically relevant mutations, including HER2 YVMA, the most common exon 20 insertion mutation, prevalent in HER2 mutant NSCLC. ELVN-002 is a potent, irreversible inhibitor of HER2 with a >100-fold selectivity over EGFR. ELVN-002 potently inhibits the phosphorylation of HER2 in cell lines endogenously expressing HER2 or in those engineered to express specific clinically relevant HER2 mutants. This activity readily translates into marked anti-proliferative activity against cell lines dependent upon HER2 for their growth and survival. In addition, ELVN-002 is highly selective for HER2 and HER2 mutants versus wild-type EGFR as demonstrated via assessment of both EGFR-driven proliferation and EGFR phosphorylation in cells. Furthermore, ELVN-002 is highly active in mouse models of HER2-driven cancers, including subcutaneous models driven by wild type or mutant HER2. ELVN-002 is also active in an NCI-N87 wild-type HER2 intracranial model. In all models tested, ELVN-002 treatment is well tolerated and resulted in tumor regressions at exposures believed to be clinically achievable. Due to its selectivity and breadth of activity versus the clinically relevant HER2 mutants, ELVN-002 has the potential to be an effective treatment for HER2 mutant NSCLC as well as other HER2 mutant amplified solid tumors, including metastatic HER2 positive breast cancer. Additionally, ELVN-002 could provide a meaningful therapeutic option for patients with CNS metastases. ELVN-002 has been selected for clinical development. Citation Format: Monette Aujay, Amanda J. Broad, Stefan D. Gross, Li Ren, Joseph P. Lyssikatos, Samuel Kintz, Qi Wang, Helen Collins. Preclinical activity of ELVN-002: A potent, selective, and irreversible HER2 and pan-HER2 mutant small molecule inhibitor for the treatment of HER2 driven malignancies. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4019.

P288 Is it safe to discontinue long-term trastuzumab containing therapy after radiological complete response (rCR) in metastatic HER-2 positive breast cancer (MBC)?

P288 Is it safe to discontinue long-term trastuzumab containing therapy after radiological complete response (rCR) in metastatic HER-2 positive breast cancer (MBC)?

A phase I trial of palbociclib and bosutinib with fulvestrant in patients with metastatic hormone receptor positive and HER2 negative (HR+ HER2-) breast cancer refractory to an aromatase inhibitor and a CDK4/6 inhibitor

Standard treatment for metastatic hormone positive (HR+) breast cancer includes a combination of a CDK4/6 inhibitor and antiestrogen therapy. Despite durable responses, eventual endocrine resistance results in disease progression. The Src/Abl pathway has been shown to mediate endocrine resistance in breast cancer, thus providing a promising target for novel therapies. Bosutinib is a tyrosine kinase inhibitor that targets the Src/Abl pathway, which has been studied in hematologic malignancies. Preclinical data suggests that the addition of bosutinib to a CDK4/6 inhibitor and antiestrogen therapy has the potential to reverse endocrine resistance.This is a phase I, single arm, open-label clinical trial in which we evaluate the combination of palbociclib and fulvestrant with bosutinib in metastatic HR+ breast cancer. Patients with confirmed advanced HR+/HER2- breast cancer who have received no more than three lines of chemotherapy and have progressed on at least one aromatase inhibitor and one CDK4/6 inhibitor will be enrolled. Participants will be given a combination of palbociclib, fulvestrant and bosutinib over 28-day cycles. The primary objective of this study is to assess the safety and tolerability of bosutinib in combination with palbociclib and fulvestrant in the study population. Secondary objectives are to 1) determine the anti-tumor effect of this therapeutic combination by assessing overall response rate (ORR) and clinical benefit rate (CBR) after 6 months of treatment, 2) to determine the clinical pharmacology parameters of bosutinib in this regimen, and 3) to build a tissue repository at Georgetown Lombardi Comprehensive Cancer Center for further translational study.

Abstract P4-01-20: Phase IV study evaluating talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a somatic or germline BRCA1/2 mutation (ViTAL) – Analysis of cohort 1 according to hormonal receptor status

Abstract Background: Talazoparib (TALA) is a highly potent, dual-mechanism PARP inhibitor that has demonstrated clinical benefit in EMBRACA Phase III trial for patients with germline BRCA1/2 mutated locally advanced or metastatic HER2- breast cancer. Objective: The aim of the study is to ensure the effectiveness and safety of TALA in real-life setting among patients with locally advanced or metastatic HER2- breast cancer, with somatic or germline BRCA1/2 mutation. Methods: ViTAL is an ambispective, multicentric, longitudinal, phase IV study. It includes two ambispective cohorts: - Cohort 1: patients treated through the French Early Access Program and inclusion of patients with somatic BRCA1/2 mutation was allowed. - Cohort 2: patients treated according to the European Marketing Approval granted in 09/21/2021. Here we present the results of the primary and some secondary endpoints for cohort 1. Results: From November 2018 to May 2021, 86 patients were included in Cohort 1, with updated results after a median follow-up of 17.3 months (11.2 - 24.4). Patients’ characteristics are 53.5% of ER+ BC/46.5% of TNBC (refer to the table). The median Time to Treatment Discontinuation (mTTD) was 9.0 months [range 6.0; 11.5] with 37.7% of patients still on treatment at 12 months. Subgroup analysis shows similar mTTD according HR status, germline vs somatic mutation and prior platinum exposure (refer to the table). The Clinical Benefit Rate assessed by the investigators is 82.4% (Complete Response for 25.7%, Partial response R for 32.4% and stable disease for 24.3%). The median of duration of CNS metastases control was 6.6 months, and 80.0% of patients had control of CNS metastases during TALA. Out of the 85 treated patients, 69 patients (80,2%) experienced a TALA permanent discontinuation for progressive disease (84.1%), toxicity (10.1%), cancer-related death (1.4%), or other reasons (1.4%). After discontinuation of TALA, 65.1% of patients received a subsequent treatment with a TTD of 2.3 months [1.7; 2.7]. The most common subsequent treatments were non-platinum chemotherapy (64.3%), platinum chemotherapy (19.6%) and others (19.1%). At least one adverse events (AEs) was recorded in 74.4% of patients. Hematologic AEs (any grade) occurred in 48.8% (anemia 27.9%, thrombocytopenia 12.8%, neutropenia 10.5%). Most common non-hematologic AEs were alopecia (8.1%) and asthenia (7.0%). Related Serious Hematologic AEs occurred in 10 patients (11.6%) including 7 (8.1%) Anemia. Related Serious Non-hematologic AEs (vomiting, pyelonephritis and ascitis) were seen in 3 patients (3.6%). AEs associated with temporary drug interruption, dose modification and permanent drug discontinuation occurred in 36 (41.9%), 24 (27.9%), and 7 (10.1%) patients respectively. The mOS is expected to be reached at the time of the congress, with 51.9% of patients still alive at 24 months. Conclusions: ViTAL is the largest study that reports real-word data with TALA. Outcomes and safety in Cohort 1 are consistent with the results of EMBRACA study and give additional data on subgroups of interest (ie patients previously treated with carboplatin, presence of CNS). (Litton et al. NEJM 2018) mTTD on subgroups of interest Patients’ characteristics Citation Format: Delphine Loirat, Marie Duboys de la barre, Jean-Christophe Thery, Ioana Hrab, Christelle Jouannaud, Jean-Loup Mouysset, Laura Salabert, Pauline Soibinet, Audrey Mailliez, Romain Valery, Anne Creisson, Cristian Villanueva, Nadine Dohollou, Jean-david Fumet, Thomas grellety, Nathalie Perez-staub, Emma Lachaier, Aurore Iltis-roux, Miguel delbado, Abeer Najem, Romuald Le Scodan, Elsa Curtit, kais aldabbagh, Pascal Pujol, thibault DE LA MOTTE ROUGE. Phase IV study evaluating talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a somatic or germline BRCA1/2 mutation (ViTAL) – Analysis of cohort 1 according to hormonal receptor status [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 P4-01-20.

Abstract P4-01-04: Phase IV multicenter study evaluating RWE and the safety of talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a BRCA1/2 mutation (ViTAL) - Cohort 2: patients treated according to the EMA

Abstract Background: Talazoparib (TALA) is a highly potent, dual-mechanism PARP inhibitor that has demonstrated clinical benefit in EMBRACA Phase III trial for patients with germline BRCA1/2 (BRCA1/2)-mutated locally advanced or metastatic HER2- breast cancer. Objective: The aim of the study is to ensure the effectiveness and safety of TALA in the real-world setting among patients with locally advanced or metastatic HER2- breast cancer, with somatic or germline BRCA1/2 mutation. Methods: ViTAL is an ambispective, multicentric, longitudinal, phase IV study. It includes two ambispective cohorts: - Cohort 1: patients treated through the French Early Access Program and inclusion of patients with somatic BRCA1/2 mutation was allowed. - Cohort 2: patients treated according to the European Marketing Approval granted in 09/21/2021. The primary endpoint of the study is the Time to Treatment Discontinuation (TTD) which is defined as time between the date of first dose of TALA and the date of last dose or death. Results: From November 2018 to May 2021, 85 patients were included in Cohort 2, Patients’ characteristics are: - a median age of 49.0 years; - 65.8% ER+ BC/34.2% TNBC; - 42.1% mBRCA1/55.3 % mBRCA2/2,6% mBRCA1 and mBRCA2. - 85.7% ECOG PS 0 or 1; - 23.4% de novo mBC. - Visceral, bones and CNS metastases were found in 59.0%, 61.5% and 10.3% of patients respectively. - No breast or ovarian cancer family history at 1st degree was found in 39 patients (50.0%). - 38.5% were chemo-naïve; - 21.8% received prior platinum in (neo)adjuvant or metastatic setting, with a median of prior cytotoxic regimen of 1 - For patients with ER+/HER2- ABC the median number of prior endocrine therapy was 1 and 62.0% of these patients received a CDK4/6 inhibitor prior to TALA. - 8 patients (10.3%) had CNS metastases. Out of the 78 treated patients, 57 patients (73.0%) experienced a TALA permanent discontinuation for Progressive disease (80.7%), toxicity (12.3%), cancer-related death (1.8%), or other reasons (1.8%). The median TTD for TALA is 9.6 months [6.7;10.8] with 34.5% of patients still on treatment at 12 months. After discontinuation of TALA, 59.0% of patients received a subsequent treatment with a TTD of 3.9 months [2.1; 45]. The most common subsequent treatments were non-platinum chemotherapy (67.4%), platinum therapy (6.5%) and other (26.1%). The Clinical Benefit Rate assessed by the investigators is 87.6% (Complete Response for 14.1%, Partial Response for 56.3% and Stable Disease for 17.2%). The median duration of CNS metastases control was 10.2 months, and 25.0% of patients had a control of CNS metastases. At least one adverse events (AEs) was recorded in 67.9% of patients. Hematologic adverse events (AEs) (any grade) occurred in 55.1% (anemia 37.2%, thrombocytopenia 16.7%, neutropenia 15.4%). Most common non-hematologic AEs were Nausea (15.4%) and asthenia (15.4%). Related Serious Hematologic AEs occurred in 6 patients (7.7%) including 3 (3.8%) thrombocytopenia and 3 (3.8%) anemia. Related Serious Non-hematologic AEs (metrorrhagia) were seen in 1 patient (1.3%). AEs associated with temporary drug interruption, dose modification and permanent drug discontinuation occurred in 26 (33.3%), 22 (28.2%), and 7 (12.3%) patients respectively. The mOS is not mature for this analysis. Conclusions: ViTAL is the largest study that reports real-word data with TALA. Outcomes and safety in Cohort 2 (patients treated with TALA according to the European Marketing Approval), are consistent with the results of EMBRACA study and with the Cohort 1. (Litton et al. NEJM 2018) Citation Format: Delphine Loirat, Marie Duboys de la barre, Cristian Villanueva, Audrey Mailliez, Nicolas Isambert, Lionel Moreau, Emmanuelle Jacquet, Dominique Spaëth, Anne Creisson, Christelle Jouannaud, Eric Legouffe, Miguel delbado, Laura Deiana, Pauline Soibinet, Ioana Hrab, Thomas grellety, Nadine Dohollou, Raffaele Longo, Jean-Christophe Thery, Jean-david Fumet, Sellam Zineb, Pascal Pujol, thibault DE LA MOTTE ROUGE. Phase IV multicenter study evaluating RWE and the safety of talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a BRCA1/2 mutation (ViTAL) - Cohort 2: patients treated according to the EMA [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 P4-01-04.

Abstract P4-08-15: Identification of target kinases whose inhibition enhances antitumor efficacy of sacituzumab-govitecan in metastatic HER2-negative breast cancer

Abstract BACKGROUND HER2-negative (HER2−) breast cancer (BC) subtypes, such as luminal A and triple-negative breast cancer (TNBC), express human trophoblast cell-surface antigen 2 (Trop-2). A high level of Trop-2 expression is associated with a poor prognosis in solid tumors. Sacituzumab-govitecan (SG), a Trop-2–directed antibody conjugated with SN-38 (topoisomerase Ⅰ inhibitor) significantly improves survival in patients with metastatic TNBC. Also, the IMMU-132-01 phase Ⅰ/Ⅱ study revealed that SG has antitumor activity in previously treated hormone receptor (HR)+/HER2− metastatic BC. In a phase Ⅲ trial (TROPiCS-02), SG demonstrated statistically significant progression-free survival in patients with heavily pre-treated HR+/HER2− endocrine-resistant metastatic BC. To augment the efficacy of SG, we sought to identify potential kinase targets whose inhibition enhances the antitumor efficacy of SG to formulate an SG-based combination therapy. MATERIALS AND METHODS Fluorescence-activated cell sorting analysis and Western blotting were used to evaluate the expression of Trop-2 in 24 TNBC and 8 HR+ BC cell lines. Non-biased high-throughput kinome-wide RNAi screening was performed with BT-20 (TNBC) and T47D tamoxifen/abemaciclib double-resistant (HR+) cell lines to identify target kinases whose inhibition produces synergistic antitumor efficacy of SG. To validate the combination antitumor effect of SG and selected kinase target inhibitors, sulforhodamine B staining proliferation assays, cell cycle analysis, and caspase 3/7 activity assays were performed in Trop-2+ TNBC and HR+ BC cell lines, including cell lines resistant to tamoxifen and double-resistant to tamoxifen and CDK4/6 inhibitor (palbociclib or abemaciclib). RESULTS In vitro proliferation assays revealed that the half-maximal inhibitory concentration (IC50) of SG in tested TNBC cell lines ranged from 10 nM to 84 nM, and that of HR+ cell lines ranged from 12.5 nM to >250 nM. We identified 69 kinase targets in TNBC cell line BT-20 and 44 kinase targets in HR+ BC cell line T47D (tamoxifen/abemaciclib double-resistant) by the sensitivity index analysis (>0.15) of RNAi screening results, and further pathway analysis revealed DNA damage response (DDR), (drug: BAY1895344), PI3k/Akt/mTOR (drug: copanlisib), and MAPK (drug: trametinib) as potential target canonical pathways whose targeting enhanced the cytotoxic effect of SG in both TNBC and HR+ BC. Among these strategies, inhibition of the DDR pathway with ATR inhibitor (BAY1895344) yielded a synergistic antiproliferative effect in combination with SG compared to SG or BAY1895344 alone in all tested TNBC and HR+ BC cell lines. Growth inhibition by SG combined with BAY1895344 averaged 97.1% in TNBC cell lines and ranged from 30.7% to 81.3% in HR+ BC cell lines, with P< 0.001. Other combinations with SG showed partially synergistic antiproliferative effects (copanlisib: effective in 3 of 5 cell lines, trametinib: effective in 2 of 5 cell lines). CONCLUSIONS RNAi screening uncovered DDR, PI3k/Akt/mTOR, and MAPK pathways as potential targets for combination with SG. Among inhibitors of these targets, DDR pathway inhibitor BAY1895344 had the most robust synergy with SG, compared to two other target inhibitors, against Trop-2+ TNBC and HR+ BC cell lines. These in vitro data warrant future in vivo validation studies of the synergistic antitumor effect of SG and BAY1895344 in metastatic HER2– breast cancer. Citation Format: Nakyung Oh, Jon A. Fuson, Huey Liu, Debu Tripathy, Naoto T. Ueno, Jangsoon Lee. Identification of target kinases whose inhibition enhances antitumor efficacy of sacituzumab-govitecan in metastatic HER2-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-15.

Abstract P4-01-37: Discontinuation of HER2+ targeted therapy among cancer survivors with metastatic HER2+ breast cancer: A case report

Abstract Background: Anti-HER2 directed therapy (aHER2tx) has significantly improved survival outcomes in patients with HER2-positive metastatic breast cancer (HMBC). Current United States (US) and European oncology practice guidelines recommend continuing aHER2tx until intolerable side effects or disease progression. It is estimated that 10-15% of treated patients (pts) may achieve prolonged complete remission (CR). Currently, the optimal duration of aHER2tx in patients achieving a CR is unknown. A PubMed literature search identified 7 case reports outside of the US that describe pts who remain in CR after discontinuation of aHER2tx. To our knowledge, this is the first analysis of similar cases in the US. Method: We identified pts with a diagnosis of HMBC who discontinued aHER2tx between January 1, 2010, to June 30, 2021, at a large integrated healthcare system in the US. Pts were included if they had discontinued aHER2tx for at least one year. Data collection included demographics, histology, confirmed sites of metastatic disease (mets), local and systemic treatment (tx) before and after aHER2tx discontinuation, documented radiographic response, and reason to discontinue aHER2tx. Data collection ended on June 30, 2022. Results: Our case report identified 15 pts (mean age at diagnosis 53.0 ± 13.2) based on inclusion criteria. Baseline demographics and characteristics are listed in Table 1. Common clinical characteristics of the cohort include mean age at mets diagnosis is 56 years, postmenopausal status (67%), invasive ductal carcinoma (87%), ER-negative (60%), HER2-positive 3+ by IHC (93%), de-novo mets (60%), multiple sites (93%) and multi-organ mets (87%). Among the cohort, 6 pts (40%) received prior adjuvant therapy, then later recurred, and of these only one had received HER2-based adjuvant tx. In all pts, first line therapy for mets included chemotherapy and aHER2tx, except one pt received endocrine therapy (ET) and aHER2tx. A CR was achieved in all but one pt (93%) with one line of aHER2tx consisting of trastuzumab (H) ± pertuzumab (P). One pt (7%) received local tx to all metastatic sites. In 13 pts, the median time to first radiologic complete response (RCR) after first line therapy for mets was 4 months (Interquartile (IQR) 3-15). Two cases were not included as we were unable to determine time to initial response after tx. All pts had confirmed RCR at the time of aHER2tx discontinuation. Median duration of aHER2tx was 8.3 years (IQR 4.8-9.5), including a median of 6.3 years (IQR 2.8-8.8) on maintenance aHER2tx. Twelve pts (80%) were off all therapy, and 3 pts (20%) continued ET for ER+ disease at the last follow-up (f/u). Patient preference (47%) was the most common reason for stopping aHER2tx. The median disease-free survival off aHER2tx was 4.8 years (IQR 3.1-6.2) and all pts were alive without evidence of disease at last f/u. Conclusion: A subset of HMBC pts successfully discontinued aHER2tx without experiencing recurrence with a median of 4.8 years off therapy in a US cohort. In this case report, common clinical features like strong HER2 overexpression, no prior aHER2tx, and achieving RCR while on first line aHER2tx with H ± P are potential indicators for prolonged CR after discontinuing aHER2tx. Future studies with a comparator group are needed to fully understand the pt population who may safely stop aHER2tx after a CR. Table 1: Baseline Demographics and Clinical Characteristics Citation Format: Lai Fong Hui, Nina N. Shah, Rita L. Hui. Discontinuation of HER2+ targeted therapy among cancer survivors with metastatic HER2+ breast cancer: A case report [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 P4-01-37.

Abstract P5-02-11: Immune cell profile of tumors from patients with metastatic (met) HER2+ breast cancer (BC) with < 30 months overall survival (OS)

Abstract Background: The “Thousand Patient HER-2 database” project at Saint Vincent’s University Hospital (SVUH) Dublin has been used to identify HER2+ BC patients with durable complete response (never relapsed) to trastuzumab-based therapy. ~10% of met HER2+ BC patients achieve a durable complete response to trastuzumab, meaning the majority of patients progress on treatment. Higher stromal tumour immune infiltrate has been associated with longer OS in met HER2+ BC. There is limited tumor immune profile and PD-1 expression data available for patients with met HER2+ BC with short OS. Using the SVUH database, we have identified a preliminary cohort of 21 met HER2+ BC patients that received trastuzumab and had an OS < 30 months. This study examines the levels of pan T cell marker CD3, cytotoxic T cell marker CD8, Natural Killer (NK) cell marker CD56 and immune checkpoint PD-1 by immunohistochemistry (IHC) in this preliminary cohort. Methods: Formalin-fixed, paraffin-embedded (FFPE) biopsy specimens (n=21 primary, n=7 matched metastatic biopsies) and associated clinico-pathological data were curated. Tumor biopsies were processed for IHC staining of CD8 (Agilent IR62361-2), CD3 (Agilent IR50361-2), CD56 (Agilent IR62861-2) and PD-1 (Roche 07099029001). PD-1 staining was available for 20/21 samples. Staining was performed using the DAKO Link 48 Autostainer as per the manufacturer’s instructions using positive (tonsil tissue) and negative controls (isotype controls). Slides were processed using the Aperio AT2 Digital Slide Scanner (Leica Biosystems), reviewed using Aperio ImageScope 12.4 software (Leica Biosystems) and analyzed in QuPath (University of Edinburgh). Images were annotated to outline tumor areas and an algorithm was trained to identify cells and classify them as either tumor or stromal. Data was expressed as number of positively stained cells/mm2 breast tumor or stromal tissue. Survival studies utilized the Kaplan Meier method. The paired Student’s T test was utilized for primary vs metastatic site comparisons. Results: Designating samples with > 1 stained cell/mm2 breast tumor as positive (pos) and zero stained cells as negative (neg), 19/21 (90.5%) primary samples were pos for CD3, 15/21 (71.4%) for CD56, 14/21 (66.6%) for CD8, and 10/20 (50%) for PD-1. Within the stromal compartment, 20/21 (95.2%) primary samples were pos for CD8, 18/21 (85.7%) for CD56, 16/21 (76.2%) for CD3 and 8/20 (40%) for PD-1. PD-1 expression in the primary tumor (median OS PD-1pos 7.85 mo vs PD-1neg 5.39 mo, hazard ratio (HR) 0.642 (95% CI 0.256-1.613), p=0.346) or the stroma (median OS PD-1pos 8.84 mo vs PD-1neg 5.39 mo, HR 0.495 (95% CI 0.197-1.244), p=0.135) was not significantly associated with OS. When comparing matched primary and metastatic samples (n=7), increased stromal levels of CD3 (4/7), CD8 (4/7), CD56 (5/7) and PD-1 (4/7) were observed. Increased levels of CD3 and CD8 were observed for 2/7 samples, and increased levels of CD56 and PD-1 for 4/7 samples. With the exception of tumor CD8 levels which decreased, mean values for tumor and stromal CD3, CD56, PD-1 and stromal CD8 levels were higher in metastatic sites but all differences were not found to be significant (p>0.05). Conclusions: Our results suggest that met HER2+ BC patients with < 30 months OS have significant T cell and NK cell presence in the tumor and stromal compartments in both primary and metastatic sites. Further expansion of this limited dataset is planned to gain greater insight in to the immune cell profiles and PD-1 status of met HER2+ BC patients with short OS. Citation Format: Denis M. Collins, Janet McCormack, Laura P. Ivers, Jose Javier Berenguer Pina, Jo Ballot, Cecily Quinn, Darko Skrobo, Alex J. Eustace, Naomi Walsh, Aurelie Fabre, John Crown. Immune cell profile of tumors from patients with metastatic (met) HER2+ breast cancer (BC) with < 30 months overall survival (OS). [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 P5-02-11.

Abstract P4-02-01: Efficacy of HER2 ADCs against HER2 inhibitor resistance alterations in the PI3K and MAPK pathways in HER2-positive breast cancer

Abstract Background: HER2 positive (HER2+) breast cancers harboring downstream MAPK or PI3K pathway alterations manifest persistent downstream signaling on anti-HER2 inhibitors with metastatic patients having worse outcomes on first line trastuzumab and pertuzumab (HP) therapy. However, HER2 antibody-drug conjugates (ADCs) are not as dependent upon potent signal transduction inhibition to exert their antitumor effects. To further investigate, we sought to determine whether MAPK and/or PI3K alterations affect the biologic or clinical outcomes of patients and models receiving HER2 ADCs. Methods: We performed prospective genomic sequencing using MSK-IMPACT on patients with advanced HER2+ breast cancer who received trastuzumab emtansine (T-DM1) in the metastatic setting between March 2013 and July 2021. We collected detailed information on clinical outcomes and correlates through our institutional IRB-approved retrieval process. HER2/ER/PR status at the time of metastatic recurrence were defined as per ASCO/CAP guidelines. Cox proportional hazard models were used to determine the association between MAPK and PI3K pathways alterations and progression-free survival (PFS) on T-DM1. Common mutations associated with outcomes were modeled in HER2+ breast cancer cell lines using short hairpin RNAs and CRISPR/Cas9, and the sensitivity to HER2 ADC was evaluated via cell proliferation and xenograft assays. Results: We identified 185 HER2+ breast cancer patients treated with T-DM1 at any line (median: 5) whose primary (N=65) or metastatic (N=120) tumor samples were sequenced. Median age was 55 (range: 20-87). The majority of the patients received T-DM1 in 2nd or 3rd line (52%) and received prior trastuzumab or HER2 TKI in metastatic setting (96%). 74/185 (40%) had de novo metastatic breast cancer and 119/185 (64%) had ER/PR+/HER2+ disease. Pathogenic activating alterations involving the MAPK pathway were observed in 14% of patients with the most frequent alterations being ERBB2 activating mutations (42%) and NF1 loss (34%). PI3K pathway alterations were identified in 42% of the patients, the majority being activating mutations of PIK3CA (87%). MAPK alterations were significantly enriched in the metastatic tumors compared to the treatment-naïve primaries (20% vs 3%, p=0.001), while PI3K alterations were not (44% vs 40%, p=0.6). To reduce the possible confounding resistance mechanisms induced by prior treatment, we restricted the survival analyses to patients who received T-DM1 up to 3rd line of therapy (N=100). On multivariable analysis adjusted for ER/PR status (positive vs negative), stage at the presentation of metastatic disease (de novo metastatic vs recurrence), treatment line and type of sequenced sample (primary vs metastatic), patients with MAPK (N=14) and PI3K (N= 38) alterations had similar PFS compared to wild type (HR 1.20, 95%CI 0.62-2.30, p=0.6 and HR 1.23, 95%CI 0.77-1.95, p=0.4, respectively). Similar results were found in the combined analysis including alterations in either pathway (N=48, HR 1.28, 95%CI 0.81-2.04, p=0.3). To verify the antiproliferative effect of HER2 ADCs on breast cancer cells with MAPK pathway activation, we depleted NF1 in a panel of HER2+ breast cancer cell lines. Consistently, MAPK-altered cell lines were sensitive to FDA-approved HER2 ADCs including trastuzumab deruxtecan (T-DXd). Conclusions: In contrast to H/P therapy, T-DM1 therapy was equally effective in tumors with downstream PI3K or MAPK alterations and wild type tumors. Expanded analysis on a larger cohort, including a subgroup of patients treated with novel HER2 ADCs such as T-DXd will be presented. The characterization of PI3K and MAPK pathways status in metastatic HER2+ breast cancer may inform prioritization of treatment options. Citation Format: Emanuela Ferraro, Anton Safonov, Yuan Chen, Charlie White, Antonio Marra, Mehnaj Ahmed, Barbara Acevedo, Chau T Dang, Shanu Modi, David B. Solit, Larry Norton, Mark E. Robson, Jorge Reis-Filho, Sarat Chandarlapaty, Pedram Razavi. Efficacy of HER2 ADCs against HER2 inhibitor resistance alterations in the PI3K and MAPK pathways in HER2-positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-02-01.

Abstract P3-02-06: Demographic and clinical features of patients with metastatic HER2 positive breast cancer: a retrospective multicenter registry study of the Turkish Oncology Group

Abstract Background: Although HER2 is an aggressive subtype of BC, the outcomes have improved over the past two decades due to advances in targeted therapies. Here, we present data of HER2-positive subset from the multicenter registry study of the Turkish Oncology Group (TOG) for metastatic breast cancer with an evolving treatment landscape for over a decade (MBC). Methods: The study of TOG for MBC was a retrospective registry study aimed to collect the data of adult metastatic BC patients diagnosed between 2010-2019, at seven tertiary oncology clinics in Turkey. Patient and disease characteristics were recorded from chart reviews. HER2 (+) was defined as IHC scores of IHC3+ or IHC2+ and ISH (+). Overall survival (OS) and progression-free survival (PFS) were calculated by the Kaplan-Meier method. Correlations between demographic, prognostic variables and survival outcomes were carried out in database aggregates comprising of cohorts based on disease presentation (recurrent vs de-novo) and the diagnosis date of MBC (Cohort I: patient diagnosed between January 2010-December 2014 and Cohort II: between January 2015-December 2019). Results: Of the 1381 patients analyzed over the whole period, 333 (24.1%) HER2 (+) MBC patients were identified. 55.0% of the patients were in Cohort I. The majority (56.8%) had de novo MBC. Despite a decreasing frequency over time (63.4% in Cohort I vs 48.7% in Cohort II, p=0.007), this was the largest group with among all pathological subgroups presenting with de novo disease. 17 patients (2.4% of recurrent patients) demonstrated changes in HER2 receptor status from negative to positive between the primary tumor and subsequent metastasis. Recurrent BC patients were significantly younger than de novo MBC patients [44 (22-80) years vs 49 (20-91) years, p=0.006] and 43.1% (n=62) had relapsed within two years from initial diagnosis. Recurrent BC patients showed a higher frequency of brain metastasis as compared to de novo patients (13.2% vs 1.1%), whereas non-CNS visceral organ metastases were more common in de novo MBC patients (58.7% vs 47.9%, respectively, p< 0.001). Following conditional approval of use in de novo visceral metastatic disease in 2016, dual-HER2 blockade including pertuzumab was more frequently used in Cohort II compared to Cohort I (p< 0.001). Although overall median PFS was not statistically significant between the two cohorts (Cohort II vs I; 22 vs 17 months, respectively, p=0.609), there was a significantly higher PFS in the de novo group in Cohort II (29 vs 17 months, p=0.037). Furthermore, there was a significant improvement in median OS in Cohort II compared to Cohort I [not reached vs 48.0 (40.0-71.0) months, respectively; p=0.017]; mainly driven by the de novo group in alignment with the approval indication for dual blockade (Cohort I vs II; 3-year OS; 62.0% vs 84.7%; p=0.009); especially those with visceral metastatic presentation (59.4% vs 83.4%, p=0.020); HR (+) HER2 (+) disease (61.2% vs 89.2%; p=0.013) and age< 40 years (40.0% vs 94.7%; p=0.009). Conclusion: There was a significant survival benefit achieved in patients with metastatic HER2 (+) disease over time, regardless of high-risk factors such as visceral involvement or young age, mirroring advances in the timeline of anti-HER2 treatment. Citation Format: Yeşim ERALP, İzzet DOĞAN, Sercan Aksoy, Burcu ÇAKAR, Gül BAŞARAN, Özlem ERCELEP, Nil MOLİNAS MANDEL, Taner KORKMAZ, Erhan GÖKMEN, Adnan AYDINER, Pınar SAİP. Demographic and clinical features of patients with metastatic HER2 positive breast cancer: a retrospective multicenter registry study of the Turkish Oncology Group [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 P3-02-06.

Abstract P1-11-04: Assessing the clinico-pathological characteristics of HER2 positive metastatic breast cancer patients experiencing radiologic complete response in a nationwide cohort

Abstract Background: Up to 6% of patients (pts) with HER2 positive (pos) metastatic breast cancer (MBC) experience a radiologic complete response (rCR) to a first line of therapy, but these results mostly derive from dated and/or limited cohorts. Aim of this study was to define the clinico-pathological characteristics of HER2 positive (pos) MBC pts experiencing a rCR. Methods: Pts were selected from the database of the GIM14 study (NCT02284581) and classified according to the best radiologic response obtained to the first line chemotherapy (CT) and upon time-to-treatment-failure (TTF). rCR was defined as complete response (CR) with a TTF > 3 months. The association across variables was tested through logistic regression and their prognostic impact in terms of overall survival (OS) was estimated using the Kaplan-Meier method and compared using the log-rank test. Results: Of the 3,423 pts included in the GIM14 study, 814 had HER2 pos MBC. After exclusion of pts treated with first line endocrine therapy and/or with TTF < 3 months, 656 pts were included in the present analysis, of which 96 (14.6%) experienced a rCR. Instead, the best response was a partial response for 295 pts (45.0%), stable disease for 221 pts (33.7%), and progression for 44 pts (6.7%). Most pts (59.8%) presented de novo MBC; 379 pts (57.8%) had visceral metastases (mets), 609 pts (92.8%) did not have central nervous system (CNS) involvement and 318 pts (48.5%) had only 1 site of distant mets. Also, 445 pts (67.9%) had hormone receptor (HR) pos disease, a HER2 3+ score at immunohistochemistry (IHC) was present in 59.8% of cases versus 40.2% with HER2 2+ at IHC and in situ hybridization (ISH) + disease. Taxanes were the main CT backbone (489 pts, 74.5%), 341 pts (52.0%) had received a Trastuzumab-Pertuzumab doublet. At multivariable analysis, higher odds of experiencing a rCR were reported for presence of non-visceral mets (OR 1.87, 95%CI 1.10-3.17), low number of metastatic sites (OR 2.42, 95%CI 0.80-7.33 for 1 site only) and HER2 3+ score at IHC (OR 1.80, 95%CI 1.09-2.98). Disease-free interval (DFI) was associated to rCR at univariable but not at multivariable analysis. HR status, CT backbone and type of anti-HER2 regimen were not associated with rCR neither at univariable nor at multivariable analysis. Median follow-up was 76.2 months. Amongst pts with TTF>12 months, those with rCR had a significantly higher OS compared to those not experiencing a rCR (median OS 133 and 90 months, respectively; p=0.0191). OS rates in pts with TTF ≥ 12 months were 97.8% at 2-year follow-up and 59.4% at 5-year follow-up. Instead, in pts with TTF ≥ 60 months, OS rates were 76.7% at 10-year follow-up. Amongst the 96 pts experiencing a CR, 38 had a rCR with TTF between 12 and 60 months, while 22 pts had a rCR with a TTF ≥ 60 months. The remaining pts had a CR with a TTF < 12 months. Pts with HR negative (neg) disease were found to be more likely to experience a rCR with a with TTF between 12 and 60 months, whilst pts with HR pos disease had a higher probability to experience a rCR with a TTF ≥ 60 months (p=0.0074). Pts with HER2 3+ score at IHC had a higher probability to achieve a rCR with a TTF ≥ 12 months compared to pts with HER2 2+ score at IHC and ISH + (p=0.0216). Age at diagnosis, menopausal status, DFI, number and site of mets, CT backbone and anti-HER2 therapy did not influence the duration of the rCR obtained. Conclusions: This study characterized a real-world cohort of HER2 positive MBC patients experiencing radiologic complete response to a first line treatment. Based on these results a clinical trial focused on liquid biopsy-based minimal residual disease is being designed. Novel anti-HER2 agents are gaining momentum as ever increasingly effective treatments and future de-escalation strategies after complete response will represent a growing need. Citation Format: Linda Cucciniello, Eva Blondeaux, Claudia Bighin, Simona Gasparro, Stefania Russo, Arianna Dri, Palma Pugliese, Andrea Fontana, Giuseppe Naso, Antonella Ferzi, Ferdinando Riccardi, Valentina Sini, Luca Boni, Alessandra Fabi, Filippo Montemurro, Michelino De Laurentiis, Grazia Arpino, Lucia Del Mastro, Lorenzo Gerratana, Fabio Puglisi. Assessing the clinico-pathological characteristics of HER2 positive metastatic breast cancer patients experiencing radiologic complete response in a nationwide cohort [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-11-04.

Abstract P6-01-29: Serial genomic analysis of circulating free DNA and change of immune-related gene signature in triple negative and HER2 positive advanced, metastatic breast cancer

Abstract Background: Circulating tumor cells (CTCs) and circulating free DNA (cfDNA) have a promising role for detecting early response and progression in breast cancer. Furthermore, change of immune-related gene signature during systemic treatment influence the treatment response of breast cancer. Herein we report the outcome of serial genomic analysis of CTC, cfDNA and change of immune-related gene signature in advanced, metastatic triple negative breast cancer (TNBC) and HER2 positive breast cancer (BC). Methods: Serial whole blood were prospectively collected in 18 early or advanced, and 10 metastatic BC patients periodically during systemic chemotherapy. CTC was isolated from whole blood through EpCAM positive bead selection, and ctDNA was isolated from plasma. For genomic profiling of CTC and ctDNA, Oncomine™ Comprehensive Assay Plus and Oncomine™ Pan-Cancer cfDNA assay (included BRCA1, BRCA2 and MYCN customized panel) was performed and analyzed, respectively. Total RNA was extracted using whole blood and analyzed using Nanostring Pancancer Immunology Panel. Results: Total 61 serial samples were obtained from 28 patients during the study. At baseline, FGFR4 mutation was the most commonly detected (10 patients, 76.9%) with median variant of allele frequency (VAF) of 54.5% (range 20.87~99.8%) in advanced and metastatic TNBC based on CTC analysis. In case of cfDNA, 11 patients (84.6%) showed TP53 mutation with low VAF (median 1.8%, range 0.1~12.3%). In HER2 positive BC, FGFR4 was also the most common mutation (5 patients [62.5%]; median VAF 57.9%) in CTC analysis and TP53 was most frequently detected (5 patients, [62.5%]; median VAF 3.0%) in cfDNA analysis. In three pathogenic gBRCA1 mutated patients, BRCA1 was identically detected in 2 patients based on CTC analysis and in 3 patients based on cfDNA analysis with VAF of approximately 50%. There were no significant changes of VAF in target mutations of CTC and cfDNA during systemic treatment, irrespective of tumor response and subtype. However, in one patients who harbored 13 mutations detected based on baseline CTC analysis, showed disappearance of 12 mutations in final CTC analysis with partial response based on radiologic findings. In contrary, there was another patient who gained multiple mutations during CTC analysis during neoadjuvant chemotherapy (NAC) with gain of tumor mutational burden (TMB). She did not achieve pathologic complete response and RCB score was 3 after completion of NAC. Most TNBC patients who received NAC and showed partial response, TMB showed gradual decrease during treatment. Baseline immune-related gene signatures were compared between HER2(+) BC and TNBC, and type 1 interferon signaling pathway was upregulated in HER2 (+) BC compared to TNBC. Conclusions: Our study suggest that serial follow up CTC and ctDNA, immune-related gene signature is feasible and reflect the general characteristics of baseline characteristics and dynamic molecular alteration of breast cancer. Further analysis with larger patient sample and correlation with tumor tissue is warranted in the future. Citation Format: Jieun Lee, Kabsoo Shin, Seung Yeon Joe, Hayoon Lee, Byung Hee Jeon, Ahwon Lee. Serial genomic analysis of circulating free DNA and change of immune-related gene signature in triple negative and HER2 positive advanced, 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 P6-01-29.

Abstract P1-03-04: Visceral fat area as a predictive factor in metastatic HER2 negative breast cancer patients treated by first line chemotherapy with weekly paclitaxel and bevacizumab

Abstract Background Obesity has previously been correlated with poorer survival in both early and metastatic breast cancer. Adipose tissues release proangiogenic factors such as Insulin-like Growth Factor and Vascular Endothelial Growth Factor that may ultimately promote tumor growth. CTscan can be used to measure the visceral fat area (VFA) and the subcutaneous fat area (SFA) on the same section. High VFA has been shown to independently predict poorer outcome in patients given first-line bevacizumab-based treatment for metastatic colorectal cancer and metastatic renal cell carcinoma. The prospective multicenter COMET trial included metastatic HER2 negative breast cancer patients receiving bevacizumab and paclitaxel as fist-line chemotherapy. This study was designed to identify and validate reliable factors to predict benefit of bevacizumab and allow for a more personalized use of this antiangiogenic agent. Our aim was to evaluate the prognostic value of BMI (Body Mass Index), VFA and SFA in the COMET cohort and their impact on the quality of life. Patients and Methods Out of the 510 patients included in the COMET trial from 9/2012 to 3/2016, 480 received bevacizumab and paclitaxel as first-line treatment and 360 had available CTscan data. VFA and SFA were measured retrospectively on the CTscans performed before chemotherapy initiation, at the level of the umbilicus with the patient in the supine position. ImageJ software was used to measure pixels with densities in the -190 HU to -30 HU range in order to delineate the subcutaneous and visceral compartments and to compute the cross-sectional area of each in cm2. These measurements were performed by a radiologist blinded to patients’ characteristics and outcomes. For VFA and SFA, we used a threshold at the median value. VFA and SFA levels were tested for their association with progression-free survival (PFS) and overall survival (OS). The impact on quality of life was based on the Global Health Status, the Physical functioning, the Emotional functioning, Fatigue and Pain scores. Results The mean age at inclusion was 57 years (range: 28-83). At initial diagnosis, the main histological type was invasive ductal carcinoma (n = 247, 80.7%). Most patients had received prior neoadjuvant/adjuvant chemotherapy (n = 245, 68.1%) and a large majority (95.4%) had less than 3 metastatic sites. One hundred and forty patients (46.7%) had histological grade II and 41% had grade III tumors. The majority of the patients had positive hormone receptor tumor (n = 238, 79.3 %) and 62 (20.7%) had triple-negative tumor subtype. The median BMI was 24.7 (range : 17-46). After a median follow-up of 60.6 months (95%CI, 60-61.3), median PFS was 9.5 months (95CI, 8.6-10.3). There was no significant correlation between BMI (p = 0.69), VFA (p = 0.24) or SFA (p = 0.58) and PFS in the univariate analysis. The median OS was 29.6 months (95CI, 25.9-32.4). BMI, VFA and SFA were not correlated with OS. Out of the 360 patients, 328 had available data regarding the quality of life. There was no impact of the VFA or the SFA on the different quality of life scores. Conclusions In our prospective cohort of 360 patients with metastatic breast cancer receiving bevacizumab and paclitaxel as first-line treatment, high VFA or high SFA were not associated with a poorer survival. VFA and SFA had no impact on quality of life. Citation Format: Séverine Guiu, Boris Guiu, Marion Chevrier, Oumar Billa, Christelle Levy, Olivier Trédan, Isabelle Desmoulins, Marc Debled, Jean-Marc Ferrero, Christelle Jouannaud, Anthony Gonçalves, Maria Rios, Marie-Ange Mouret-Reynier, Frédérique Berger, Fatima-Zohra TOUMI, Jérôme Lemonnier, Jean-Yves Pierga, Sandrine Dabakuyo, Sophie Gourgou. Visceral fat area as a predictive factor in metastatic HER2 negative breast cancer patients treated by first line chemotherapy with weekly paclitaxel and bevacizumab [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 P1-03-04.

Abstract P1-12-02: Unusual hepatotoxicity with the use of Ribociclib in a premenopausal patient

Abstract BACKGROUND The introduction of cyclin inhibitors in the treatment of metastatic breast cancer has completely changed the natural history of this disease. In the case of premenopausal women, the use of ovarian suppression + aromatase inhibitor or tamoxifen associated with ribociclib demonstrated not only a gain in disease-free survival, but also in overall survival, making it the first choice of treatment for premenopausal women with HER2 negative hormone receptor-positive metastatic breast cancer. Ribociclib is a very well tolerated drug. Neutropenia, the main side effect, is easily manageable in clinical practice. However, one study showed elevation of ALT and AST grade 3 or 4 in 9.3% of patients, while other studies observed that liver dysfunction was dose-limited, and therefore should always be evaluated when using this drug. The pathophysiology of liver injury, not yet fully understood, is attributed to hepatotoxic metabolites or immunogenic effects with damage to hepatocytes similar to the ones triggered by autoimmune hepatitis. There are successful case reports with re-exposure to either the same drug or another CDK4/6 inhibitor. METHODS We describe a case of a premenopausal woman with metastatic breast cancer who experienced severe hepatotoxicity with ribociclib use. When her liver function was back to normal, she did a rechallenge with a lower dose of ribociclb and had another liver disfunction. RESULTS A 34-year-old premenopausal and nulliparous woman, was diagnosed in 2020 with a hepatic and lymph nodes metastatic HER2 negative hormone receptor-positive invasive breast carcinoma, (ER 90%, PR 90%, HER2 negative, KI-67: 20%). Genetic evaluation showed pathogenic mutation in ATM and VUS in RET, and positive PIK3CA in the tumor. Her first-line treatment was according to the Monaleesa-7 trial with goserelin 3.6 mg every 28 days + letrozole 2.5 mg daily + ribociclib 600 mg/day for 21 days and a break for 7 days, without delays or dose reductions. After 3 months of treatment, with monthly laboratory tests showing normal results, a new PET-CT was performed, which showed a complete metabolic response, both in lymph nodes and in liver lesions (attached figures). In the 4th month of treatment, the patient presented symptoms of malaise, nausea, vomiting, epigastric pain, and jaundice. Laboratory tests showed: ALT 1439 (Reference value – RV: 13-35); AST 1946 (RV:10-49), Total Bilirubin 5 (RV: 1.1), INR 1.8, GGT 500 (RV< 38), ALP 651 (RV: 46-116). After extensive laboratory investigation, the hypothesis of toxicity by ribociclib was raised, which was suspended. She was started with prednisone 60 mg daily associated with ursodeoxycholic acid 300 mg BID with normalization of the hepatic profile after2 months, when PET-CT was repeated, maintaining response in all lesion foci. It was decided to reintroduce ribociclib, this time at a dose of 200 mg daily, with further laboratory worsening after 2 weeks and definitive suspension of the drug. The patient is currently with non-evidence of disease, using goserelin 3.6 mg every 28 days associated with letrozole 2.5 mg daily. Last PET-CT was performed 15 months after ribociclib discontinuation, maintaining response in all lesions. CONCLUSION Ribociclib is a great therapeutic option for the treatment of HER 2 negative HR+ metastatic breast cancer. It is generally well tolerated, however laboratory monitoring should be performed throughout the treatment period. Hepatotoxicity, although rare, may occur, with improvement after discontinuation of the drug. Citation Format: Giovanna Carlos, Bruna Zucchetti, Vanessa Donatelli, Alexandre Carlos, anezka Ferrari, Manuel Cruz, Camila Dagostim. Unusual hepatotoxicity with the use of Ribociclib in a premenopausal patient [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 P1-12-02.

Abstract P3-06-01: Unleashing NK- and CD8 T cells by combining monalizumab (anti-NKG2A) and trastuzumab for metastatic HER2+ breast cancer: first results MIMOSA trial

Abstract Background Although treatment options and survival of HER2+ metastatic breast cancer (MBC) patients have greatly improved, the majority of MBC-patients still die of this disease. The relatively high levels of TILs observed in this BC subtype provide a rationale for immunomodulatory strategies, however, PD1-blockade has only shown modest response rates in this setting. While PD-1 blockade mainly acts on T cells, monalizumab targets the inhibitory immune checkpoint NKG2A which interacts with HLA-E on tumor cells, thereby unleashing NK- as well as CD8 T cells. We hypothesize that monalizumab can promote antibody-dependent cell-mediated cytotoxicity (ADCC) which is critical for trastuzumab efficacy. Clinical activity was shown in patients with head and neck cancer when monalizumab was combined with cetuximab (anti-EGFR). Here, we present the first results of the MIMOSA-trial investigating the efficacy of the novel combination monalizumab and trastuzumab in patients with HER2+ MBC. Methods In the phase II MIMOSA-trial (NTC04307329), HER2+ MBC patients were treated biweekly with 4mg/kg trastuzumab and 750mg monalizumab. Key eligibility criteria were progressive disease despite anti-HER2 therapy, had received a minimum of one and a maximum of three lines of palliative chemotherapy, had measurable disease according to RECIST1.1, and a serum LDH-level below 500U/L. Primary endpoint was objective response rate according to RECIST1.1. Secondary endpoints included clinical benefit rate (complete response CR, partial response PR or stable disease SD for at least 6 months) according to RECIST1.1, progression-free survival, overall survival and safety. Dose-limiting toxicities were continuously monitored throughout the trial and evaluated using a pre-defined Pocock-type boundary rule. Following a Simon’s two-stage design, 11 patients were included in stage I of the trial. If two or more responders were observed, further exploration is warranted in stage II. Results Between January 2021 and April 2022, eleven women of which ten are currently evaluable were enrolled in the trial. Patients received a median of two lines of prior treatment for MBC, of which 6 out of 11 patients were treated with trastuzumab emtansine (T-DM1). The majority of patients had hormone receptor positive BC (72% of the patients) and had low levels of tumor-infiltrating lymphocytes (TILs) with a median of 1% (ranging from 1% to 20%). Patients received a median of four cycles of trastuzumab and monalizumab. Treatment was well tolerated with no dose-limiting toxicities. No objective responses were observed in the first ten out of eleven evaluable patients. Therefore, MIMOSA stage I did not meet its primary endpoint, leading to discontinuation of the trial. Conclusions The novel combination of trastuzumab and monalizumab did not induce objective responses in heavily pre-treated HER2+ MBC patients. Citation Format: Veerle Geurts, Leonie Voorwerk, Karolina Sikorska, Roberto Salgado, Koen van de Vijver, Marloes van Dongen, Inge Kemper, Ingrid A. Mandjes, Martine Heuver-mes, John Haanen, Gabe S. Sonke, Hugo Horlings, Marleen Kok. Unleashing NK- and CD8 T cells by combining monalizumab (anti-NKG2A) and trastuzumab for metastatic HER2+ breast cancer: first results MIMOSA 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 P3-06-01.