anti-HER2 Antibody-drug Conjugate Research Articles

Strategies for the treatment of hormone receptor-positive HER2-low breast cancer based on clinical practice: a round table discussion.

Human epidermal growth factor receptor 2 (HER2)-low breast cancer is a newly identified targetable subset of breast tumors, and its clinical characteristics and treatment strategies are controversial. The emergence of novel anti-HER2 antibody-drug conjugate (ADC) has brought promising approaches for HER2-low breast cancer treatment. Several clinical trials have validated the efficacy and safety of trastuzumab deruxtecan (T-Dxd) in HER2-low breast cancer at different treatment settings. The treatment timing, candidate identification, long-term management, and overcoming drug resistance are crucial questions to improve breast cancer patient survival. Here we present a clinical case of hormone receptor-positive (HR+) HER2-low breast cancer patient who experienced neoadjuvant chemotherapy, surgery, adjuvant, and first-line endocrine therapy with limited effectiveness. After the treatment failure of CDK4/6 inhibitors, the utilization of T-Dxd brought a long-term disease response and tolerable low toxicities. In this round table discussion, we summarized opinions and recommendations from breast cancer surgeons and oncologists on treatment strategies for this patient. The discussion mainly focused on the precise diagnosis of HER2-low breast cancer, treatment design at different disease status, regimens selection according to drug response, strategies consideration for overcoming drug resistance and the management of adverse events in long-term survival. These opinions would provide critical insights to improve HER2-low breast cancer treatment and offer valuable suggestions for clinical practice.

184 (PB172): Evaluation of a Novel and Highly Efficacious Anti-HER2 Antibody-Drug Conjugate for HER2-Positive Breast Cancer Treatment

184 (PB172): Evaluation of a Novel and Highly Efficacious Anti-HER2 Antibody-Drug Conjugate for HER2-Positive Breast Cancer Treatment

Unveiling the mysteries of HER2-low expression in breast cancer: pathological response, prognosis, and expression level alterations

BackgroundThe novel anti-HER2 antibody drug conjugates (ADCs) can effectively improve the long-term survival of patients with HER2-low expression breast cancer. However, pathological responses to neoadjuvant therapy (NAT) within HER2-low expression breast cancer, the relationship between pathological response and prognosis and the transformation of HER2 status are all now poorly understood.MethodsThe patients with HER2-0 and HER2-low expression breast cancer receiving NAT at Harbin Medical University Cancer Hospital between Jan. 2014 and Nov. 2018 were retrospectively explored. HER2 low expression refers to the IHC 1 + or 2 + and FISH negative. The Kappa test was utilized for analyzing the consistency rate of HER2 expression. To evaluate disease-free survival (DFS) and overall survival (OS), this research employed both the Kaplan-Meier analysis and the Cox regression.ResultsIn this study, 178 patients with HER2-0 and 344 patients with HER2-low expression breast cancer were included. In comparison with the HER2-0 group, it is shown that patients in the HER2-low group have more possibility to be younger compared to those 50 years old (P < 0.014), have more premenopausal patients (P < 0.001), a higher proportion of hormone receptor (HR) positive patients (P < 0.001), and less proportion of stage III V patients (P < 0.034). When NAT was finished, the pCR rate became 23.6% in the HER2-0 group while 22.1% in the HER2-low group, and there was also a higher pCR rate in HR- patients in comparison with that in HR + patients (P < 0.01). Considering HER2 expression inconsistency, the overall HER2 inconsistency rate was 30.4% (Kappa = 0.431, P < 0.01). Among patients initially diagnosed as HER2-0, 34% (N = 61) were re-diagnosed as HER2-low after NAT. After stratification by HR expression status, HR+/HER2-0 patients transformed to HER2-low after NAT in 37%, and 32% of HR- patients changed from HER2-0 to HER2-low. In this survival analysis, there were both better DFS rates (P = 0.009) and OS rates (P = 0.026) in the HR-/HER2-low patients in comparison with the HR-/HER2-0 patients, while the HER2-0 and HER2-low patients in the HR + group had no significant survival difference. Additionally, for non-pCR patients, there was better DFS (P = 0.029) and OS (P = 0.038) in the HER2-low group in comparison with that of the HER2-0 group, while no significant survival difference exists between pCR patients.ConclusionAfter HR stratification, there are unique clinical characteristics and prognostic outcomes in HER2-low expression breast cancer, which indicates the potential to become a specific molecular subtype of breast cancer. The significant instability of HER2-low expression status between primary tumor and residual invasive disease suggests that multiple detections of HER2 status should be emphasized in NAT strategies.

345MO IBI354 (anti-HER2 antibody-drug conjugate [ADC]) in patients (pts) with advanced solid tumors and breast cancer (BC): Results from a phase I study

345MO IBI354 (anti-HER2 antibody-drug conjugate [ADC]) in patients (pts) with advanced solid tumors and breast cancer (BC): Results from a phase I study

720MO IBI354 (anti-HER2 antibody-drug conjugate [ADC]) in patients (pts) with advanced gynecological cancers (Gynecol C): Results from a phase I study

720MO IBI354 (anti-HER2 antibody-drug conjugate [ADC]) in patients (pts) with advanced gynecological cancers (Gynecol C): Results from a phase I study

Clinical best practices in interdisciplinary management of human epidermal growth factor receptor 2 antibody-drug conjugates-induced interstitial lung disease/pneumonitis: An expert consensus in China.

Antibody-drug conjugates (ADCs) have demonstrated effectiveness in treating various cancers, particularly exhibiting specificity in targeting human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Recent advancements in phase 3 clinical trials have broadened current understanding of ADCs, especially trastuzumab deruxtecan, in treating other HER2-expressing malignancies. This expansion of knowledge has led to the US Food and Drug Administration's approval of trastuzumab deruxtecan for HER2-positive and HER2-low breast cancer, HER2-positive gastric cancer, and HER2-mutant nonsmall cell lung cancer. Concurrent with the increasing use of ADCs in oncology, there is growing concern among health care professionals regarding the rise in the incidence of interstitial lung disease or pneumonitis (ILD/p), which is associated with anti-HER2 ADC therapy. Studies on anti-HER2 ADCs have reported varying ILD/p mortality rates. Consequently, it is crucial to establish guidelines for the diagnosis and management of ILD/p in patients receiving anti-HER2 ADC therapy. To this end, a panel of Chinese experts was convened to formulate a strategic approach for the identification and management of ILD/p in patients treated with anti-HER2 ADC therapy. This report presents the expert panel's opinions and recommendations, which are intended to guide the management of ILD/p induced by anti-HER2 ADC therapy in clinical practice.

HER2 exon 20 mutant non-small cell lung cancer with complete remission of intracranial metastases with trastuzumab deruxtecan: a case report.

Trastuzumab deruxtecan (T-DXd) is a novel anti-HER2 antibody-drug conjugate formed by the combination of trastuzumab and deruxtecan. It is used in human epidermal growth factor 2 receptor (HER2) mutant breast, stomach and colorectal cancers as well as non-small cell lung cancer (NSCLC). The 58-year-old denovo metastatic NSCLC patient we will discuss here progressed with newly developing brain metastasis under first-line carboplatin/paclitaxel treatment. After next generation sequencing revealed a mutation in the ERBB2 gene located in exon 20, we administered T-DXd to our patient. While a significant improvement was observed in the clinical condition of the patient after one course of treatment, brain metastases were found to be in complete response in control screening after four courses of treatment. Systemic screening with PET/computed tomography showed nearly complete regression of the primary lesion, metastatic lymphadenopathies, and surrenal metastases. T-DXd may be successfully used in HER2 mutant metastatic NSCLC patients. In addition, it can also be successfully used in patients with central nervous system metastases with or without cranial radiotherapy.

Assessment of chemical stability of monoclonal antibody and antibody drug conjugate administered by pressurized intraperitoneal aerosol chemotherapy

Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is a new therapeutic approach for patients with peritoneal cancer. So far, most published studies investigated the administration of established cytostatic agents through PIPAC. This study aimed to evaluate the effect of PIPAC on two breakthrough anti-cancer agents, specifically anti-PD1 pembrolizumab, and anti-HER2 antibody-drug conjugate (ADC) - trastuzumab-deruxtecan. We conducted systematic analyses on samples of pembrolizumab and trastuzumab-deruxtecan at clinically relevant concentrations before and after PIPAC administration using an experimental setup of a hermetic container system, mimicking the abdominal cavity and using identical features as in clinical use. We utilized a range of chromatographic and spectroscopic techniques to explore potential alterations in the primary, secondary, and tertiary structures of the drugs, focusing on post-translational modifications resulting from the aerosolization. Our findings indicate that PIPAC did not compromise the integrity of tested biopharmaceuticals. The size variants of both drugs, assessed by size exclusion chromatography (SEC), remained unchanged. Reversed-phase liquid chromatography (RPLC) and hydrophobic interaction chromatography (HIC) revealed no significant differences in hydrophobicity variants, the average drug-to-antibody ratio (DAR), or DAR distribution before and after PIPAC treatment. Circular dichroism (CD) spectroscopy confirmed that the secondary and tertiary structures were preserved. While pembrolizumab showed no change in charge variants post-PIPAC, trastuzumab-deruxtecan exhibited a non-negligible change in the quantity of charge variants on the monoclonal antibody itself, while the payload remained unchanged. This shift could possibly be related to the metallic composition of the CapnoPen® device (made of nickel and chromium) used in PIPAC and for these experiments. Together, our results suggest that PIPAC does not alter the structure of pembrolizumab and trastuzumab-deruxtecan, paving the way for future clinical trials.

A DXd/TLR7-Agonist Dual-Conjugate Anti-HER2 ADC Exerts Robust Antitumor Activity Through Tumor Cell Killing and Immune Activation.

The emergence of trastuzumab deruxtecan (T-DXd), a new-generation antibody-drug conjugate (ADC), has profoundly altered the therapeutic paradigm for HER2-positive solid tumors, demonstrating remarkable clinical benefits. However, the combined outcomes of T-DXd with immunotherapy agents remain ambiguous. In this study, we introduce Tras-DXd-MTL1, an innovative HER2 targeting ADC that integrates the topoisomerase inhibitor DXd and a toll like receptor 7 (TLR7) agonist MTT5, linked to trastuzumab via a GGFG tetrapeptide linker. Mechanistically, Tras-DXd-MTL1 retains the DNA-damaging and cell-killing properties of topoisomerase inhibitors while simultaneously enhancing the immune response within the tumor microenvironment. This is achieved by promoting immune cell infiltration and activating dendritic cells and CD8+T cells via MTT5. In vivo evaluation of Tras-DXd-MTL1's antitumor potency revealed a notably superior performance compared with the T-DXd (Tras-DXd) or Tras-MTL1 in immunocompetent mice with trastuzumab-resistant EMT6-HER2 tumor and immunodeficient mice with JIMT-1 tumor. This improved efficacy is primarily attributed to its dual functions of immune stimulation and cytotoxicity. Our findings highlight the potential of incorporating immunostimulatory agents into ADC design to potentiate antitumor effects and establish durable immune memory, thereby reducing tumor recurrence risks. Therefore, our study offers a novel strategy for the design of immune-activating ADCs and provides a potential approach for targeting solid tumors with different levels of HER2 expression.

Depicting Biomarkers for HER2-Inhibitor Resistance: Implication for Therapy in HER2-Positive Breast Cancer.

HER2 (human epidermal growth factor receptor 2) is highly expressed in a variety of cancers, including breast, lung, gastric, and pancreatic cancers. Its amplification is linked to poor clinical outcomes. At the genetic level, HER2 is encoded by the ERBB2 gene (v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2), which is frequently mutated or amplified in cancers, thus spurring extensive research into HER2 modulation and inhibition as viable anti-cancer strategies. An impressive body of FDA-approved drugs, including anti-HER2 monoclonal antibodies (mAbs), antibody-drug conjugates (ADCs), and HER2-tyrosine kinase inhibitors (TKIs), have demonstrated success in enhancing overall survival (OS) and disease progression-free survival (PFS). Yet, drug resistance remains a persistent challenge and raises the risks of metastatic potential and tumor relapse. Research into alternative therapeutic options for HER2+ breast cancer therefore proves critical for adapting to this ever-evolving landscape. This review highlights current HER2-targeted therapies, discusses predictive biomarkers for drug resistance, and introduces promising emergent therapies-especially combination therapies-that are aimed at overcoming drug resistance in the context of HER2+ breast cancer.

Efficacy and prognosis of HER2-Low and HER2-Zero in triple-negative breast cancer after neoadjuvant chemotherapy

Mounting evidence showed that HER2-Low breast cancer patients could benefit from the novel anti-HER2 antibody–drug conjugates (ADCs) treatment, which pointed the way towards better therapy for HER2-Low patients. The purpose of this study was to describe the clinicopathological features, along with chemotherapeutic effects and survival outcomes of HER2-Low and HER2-Zero in TNBC who received neoadjuvant chemotherapy (NACT). We retrospectively evaluated 638 triple-negative breast cancer patients who were treated with neoadjuvant chemotherapy between August 2014 and August 2022. Pathologic complete response (pCR) and survival outcomes were analyzed in HER2-Low cohort, HER2-Zero cohort and the overall patients, respectively. In the entire cohort, 342 (53.6%) patients were HER2-Low and 296 (46.4%) patients were HER2-Zero. No significant difference was found between HER2-Low and HER2-Zero patients based on all the clinical–pathological characteristics. 143 cases (22.4%) achieved pCR after NACT in the overall TNBC patients. The pCR rate of the HER2-Low patients and the HER2-Zero patients was 21.3% and 23.6%, respectively, exhibiting no statistical difference (p = 0.487). The survival of pCR group after NACT significantly improved compared to non-pCR group either in HER2-Low patients or in HER2-Zero patients. Although we found that patients with HER2-Low had longer DFS than patients with HER2-Zero, there was no considerable difference (p = 0.068). However, HER2-Low patients had a dramatically longer OS than HER2-Zero patients (p = 0.012). The data from present study confirmed the clinical importance of HER2-Low expression in TNBC. Further effort is needed to determine whether HER2-Low could be a more favorable prognostic marker for individual treatment.

HER2-targeted therapies beyond breast cancer - an update.

The receptor tyrosine-kinase HER2 (also known as ErbB2) is a well-established therapeutic target in patients with breast or gastric cancer selected on the basis of HER2 overexpression on immunohistochemistry and/or ERBB2 amplification on in situ hybridization. With advances in cancer molecular profiling and increased implementation of precision medicine approaches into oncology practice, actionable HER2 alterations in solid tumours have expanded to include ERBB2 mutations in addition to traditional HER2 overexpression and ERBB2 amplification. These various HER2 alterations can be found in solid tumour types beyond breast and gastric cancer, although few HER2-targeted therapeutic options have been established for the other tumour types. Nevertheless, during the 5 years since our previous Review on this topic was published in this journal, obvious and fruitful progress in the development of HER2-targeted therapies has been made, including new disease indications, innovative drugs with diverse mechanisms of action and novel frameworks for approval by regulatory authorities. These advances have culminated in the recent histology-agnostic approval of the anti-HER2 antibody-drug conjugate trastuzumab deruxtecan for patients with HER2-overexpressing solid tumours. In this new Review, we provide an update on the current development landscape of HER2-targeted therapies beyond breast cancer, as well as anticipated future HER2-directed treatment strategies to overcome resistance and thereby improve efficacy and patient outcomes.

Development of a deep-learning model tailored for HER2 detection in breast cancer to aid pathologists in interpreting HER2-low cases.

Over 50% of breast cancer cases are "Human epidermal growth factor receptor 2 (HER2) low breast cancer (BC)", characterized by HER2 immunohistochemistry (IHC) scores of 1+ or 2+ alongside no amplification on fluorescence in situ hybridization (FISH) testing. The development of new anti-HER2 antibody-drug conjugates (ADCs) for treating HER2-low breast cancers illustrates the importance of accurately assessing HER2 status, particularly HER2-low breast cancer. In this study we evaluated the performance of a deep-learning (DL) model for the assessment of HER2, including an assessment of the causes of discordances of HER2-Null between a pathologist and the DL model. We specifically focussed on aligning the DL model rules with the ASCO/CAP guidelines, including stained cells' staining intensity and completeness of membrane staining. We trained a DL model on a multicentric cohort of breast cancer cases with HER2-IHC scores (n = 299). The model was validated on two independent multicentric validation cohorts (n = 369 and n = 92), with all cases reviewed by three senior breast pathologists. All cases underwent a thorough review by three senior breast pathologists, with the ground truth determined by a majority consensus on the final HER2 score among the pathologists. In total, 760 breast cancer cases were utilized throughout the training and validation phases of the study. The model's concordance with the ground truth (ICC = 0.77 [0.68-0.83]; Fisher P = 1.32e-10) is higher than the average agreement among the three senior pathologists (ICC = 0.45 [0.17-0.65]; Fisher P = 2e-3). In the two validation cohorts, the DL model identifies 95% [93% - 98%] and 97% [91% - 100%] of HER2-low and HER2-positive tumours, respectively. Discordant results were characterized by morphological features such as extended fibrosis, a high number of tumour-infiltrating lymphocytes, and necrosis, whilst some artefacts such as nonspecific background cytoplasmic stain in the cytoplasm of tumour cells also cause discrepancy. Deep learning can support pathologists' interpretation of difficult HER2-low cases. Morphological variables and some specific artefacts can cause discrepant HER2-scores between the pathologist and the DL model.

HER2-targeting antibody drug conjugate FS-1502 in HER2-expressing metastatic breast cancer: a phase 1a/1b trial

Currently approved HER2-targeting antibody-drug conjugates (ADCs) for HER2-positive breast cancer (BC) are associated with safety concerns. In this multicenter, single-arm, dose-escalation (phase 1a) and dose-expansion (phase 1b) phase 1 trial (NCT03944499), patients with HER2-expressing advanced solid tumors received FS-1502 (an anti-HER2 ADC) with a 3 + 3 design in phase 1a; patients with metastatic HER2-positive BC received FS-1502 at the recommended phase 2 dose (RP2D) in phase 1b. The primary end points were dose-limiting toxicities (DLTs), maximum tolerated dose (MTD) and RP2D for phase 1a and objective response rate (ORR) for phase 1b. A total of 150 patients with HER2-expressing solid tumors (n = 5) and BC (n = 145) were enrolled (female, n = 146, 97.3%). One DLT each was reported at 3.0 and 3.5 mg/kg; the MTD was not reached. The RP2D was 2.3 mg/kg once every 3 weeks. Five (3.3%) patients experienced pneumonitis; four (2.7%) had grade 3 reversible ocular events. Of 67 HER2-positive BC patients receiving the RP2D, the best ORR was 53.7% (95% CI, 41.1-66.0%), including PRs confirmed (confirmed ORR, 37.5%) and pending for confirmation. FS-1502 was well tolerated with limited ocular and pulmonary findings and demonstrated promising antitumor activity in HER2-positive BC patients.

Mechanisms of action and resistance to anti-HER2 antibody-drug conjugates in breast cancer.

Human epidermal growth factor 2 (HER2)-positive breast cancer (BC) represents nearly 20% of all breast tumors. Historically, these patients had a high rate of relapse and dismal prognosis. The advent of HER2-targeting monoclonal antibodies such as trastuzumab followed by pertuzumab had improved the prognosis of HER2-positive metastatic BC. More recently, antibody-drug conjugates (ADCs) are now reshaping the treatment paradigm of solid tumors, especially breast cancer. Tratsuzumab emtansine (T-DM1) was one of the first ADC developed in oncology and was approved for the management of HER2-positive metastatic BC. In a head-to-head comparison, trastuzumab deruxtecan (T-DXd) defeated T-DM1 as a second-line treatment. The efficacy of ADCs is counterbalanced by the appearance of acquired resistance to these agents. In this paper, we summarize the mechanisms of action and resistance of T-DM1 and T-DXd, as well as their clinical efficacy. Additionally, we also discuss potential strategies for addressing resistance to ADC.

ACE-BREAST-03: A phase 2 trial evaluating ARX788, an anti-HER2 antibody drug conjugate (ADC), for the treatment of HER2+ metastatic breast cancer (mBC) in patients who have been previously treated with trastuzumab deruxtecan (T-DXd).

TPS1123 Background: HER2-targeted ADCs revolutionized treatment for patients with HER2+ mBC. The HER2-targeted ADC, T-DXd, improved PFS and OS vs T-DM1 (trastuzumab emtansine) as second-line treatment for HER2+ mBC and is now the preferred treatment option in this setting. However, new treatment options are needed for patients with disease progression on T-DXd. Novel technological advances in design of the antibody, linker, and payload of ADCs may further improve the safety/tolerability and efficacy, widening the therapeutic window to address resistance to other anti-HER2 therapies. ARX788 is a next-generation anti-HER2 ADC stably conjugated to AS269 (a potent tubulin inhibitor). Proprietary site-specific oxime conjugation chemistry, enabled by incorporation of synthetic amino acids into the antibody construct, maximizes the delivery of the cytotoxic payload to tumor cells and minimizes systemic exposure of free payload. ARX788 has shown antitumor activity in heavily pretreated patients with HER2+ and HER2-low mBC, including those with prior T-DXd exposure. Methods: ACE-Breast-03 (NCT04829604) is a Phase 2 trial evaluating ARX788 in patients previously treated with T-DXd. The primary efficacy endpoint is response rate by RECIST v1.1. Approximately 40 patients will be enrolled. Eligible patients have HER2+ mBC and up to 5 prior treatment regimens for mBC, including T-DXd. Patients must have central laboratory-confirmed HER2+ mBC; new pre-treatment biopsies may be required. Patients with treated and stable brain metastases who are off steroids are eligible. Treatment includes 1.5 mg/kg Q3W ARX788 for up to 26 cycles or until disease progression. Tumor status is assessed every 9 weeks through 27 weeks and every 12 weeks thereafter. The study is currently enrolling in the US. Clinical trial information: NCT04829604 .

Phase Ia/Ib trial on the safety and efficacy of mobocertinib in combination with T-DM1 for patients with HER2-mutant solid tumors (WJOG16022M).

3025 Background: Safety and efficacy of HER2 tyrosine kinase inhibitor (TKI) and anti-HER2 antibody-drug conjugate (ADC) in HER2-mutant solid tumors have not been investigated. Methods: Mobocertinib, a potent HER2 TKI plus T-DM1, an anti-HER2 ADC was evaluated in this phase I study. In a dose-finding cohort (phase Ia, pIa), the maximum tolerated dose was estimated in patients (pts) irrespective of HER2 mutational status. To further establish safety and evaluate preliminary efficacy, additional pts with HER2 mutations were enrolled in a dose-expansion cohort (phase Ib, pIb). Mobocertinib of 80, 120 to 160 mg was orally administered with intravenous T-DM1 3.6 mg/kg every 3 weeks. The primary endpoint was to determine the recommended dose (RD) (pIa), and to evaluate the confirmed objective response rate (ORR) (pIb). Results: Between Nov 2022 and Jun 2023, a total of 28 pts, 6 in the pIa and 22 in the pIb were enrolled to this study (14 NSCLC; 4 cervical; 2 duodenal papilla; 2 pancreatic, median follow-up, 6.4 mo [range, 1.9 to 12.9 mo]). The median age was 54 (range, 40-84) years, 17 pts were female. Among 27 pts with HER2-mutant tumors, mutations in kinase domain were most common (66.7%). In the pIa cohort, 3 DLTs were observed with mobocertinib 120 mg, including grade 3 thrombocytopenia, grade 4 acute kidney injury, and drug withdrawal due to nausea and anorexia, while there was no DLT with 80 mg. The RD was therefore determined to be mobocertinib 80 mg plus T-DM1 3.6 mg/kg. Among 22 pts in the pIb, grade ≥ 3 AE occurred in 72.7% of pts; the common events (&gt;5%) being thrombocytopenia (50.0%), diarrhea (13.6%), and anorexia (13.6%). No interstitial lung disease/pneumonitis was observed. The ORR was 28.6%, the disease control rate (DCR) was 71.4%, and median progression-free survival (mPFS) was 3.2 mo (95% CI 1.6, 6.1) in the pIb. In 27 pts with HER2 mutations across all cohorts, the ORR was 42.3%, the DCR was 76.9%, and mPFS was 4.3 mo (95% CI 2.7, 6.7). Additionally, in 13 pts with HER2-mutant NSCLC including those who had developed resistance to trastuzumab deruxtecan, the ORR was 53.8%, the DCR was 84.6%, and mPFS was 6.1 mo (95% CI 2.9, 6.3). Conclusions: The RD of this study treatment is mobocertinib 80 mg plus T-DM1 3.6 mg. Combination therapy of HER2 TKI and HER2 ADC demonstrated feasibility and potential efficacy for HER2-mutant solid tumors. Clinical trial information: 2051220070 .

ACE-Breast-02: A pivotal phase II/III trial of ARX788, a novel anti-HER2 antibody-drug conjugate (ADC), versus lapatinib plus capecitabine for HER2+ advanced breast cancer (ABC).

1020 Background: ARX788 is a next-generation ADC of HER2 monoclonal antibody site-specifically conjugated with Amberstatin 269, a potent cytotoxic tubulin inhibitor. Here we report the interim result from this seamless phase II/III trial in patients who progressed on trastuzumab based therapy. Methods: This randomized study was conducted in HER2+ (FISH+ or IHC3+) ABC in 85 centers in China. Patients with unresectable or metastatic breast cancer pretreated with trastuzumab and taxane were randomized 1:1 to receive ARX788 (1.5mg/kg, IV, Q3W) or lapatinib plus capecitabine (LC, lapatinib 1250mg, QD; capecitabine 1000mg/m2 BID, d1-14, Q3W), stratified by previous chemotherapy lines (0-1 vs. &gt;1) and visceral metastasis (yes vs. no). ARX788 was not pre-medicated with any prophylactic measures. Primary endpoint was progress-free survival (PFS) determined by Independent Review Committee (IRC). Results: As of Dec. 21, 2022, 221 patients were randomly assigned to ARX788 and 220 to LC, and 240 PFS events occurred. Efficacy results are listed in table 1. The median PFS was 11.33 months with ARX788 versus 8.25 months with LC as per IRC (HR 0.64, p=0.0006). Treatment-related adverse events (TRAEs) of any grade occurred in 98.6% (217/220) and 99.1% (213/215) of patients, respectively. TRAEs of grade 3-5 was similar in two groups (41.4% and 40.0%, respectively), commonest being blurred vision (12.3%), dry eye (9.1%), keratopathy (5.9%) and interstitial lung disease (5.9%) with ARX788 and hand-foot syndrome (18.1%), hypokalemia (5.1%), diarrhea (4.2%) with LC. 71 patients (32.3%) had interstitial lung disease with ARX788, primarily grade 1 or 2 (26.8%) with 3 (1.4%) possibly having drug-related deaths. 164 patients (74.5%) had ocular events related to ARX788, primarily grade 1 or 2 (55.5%) with no grade 4 or 5. Conclusions: ARX788 significantly prolonged PFS comparing to LC in patients with HER2+ ABC previously treated with trastuzumab and taxane. While ocular toxicity and interstitial lung disease were common and manageable, its hematological and GI toxicities under no prophylactic premedication compared favorably with already available ADCs. Clinical trial information: CTR20201708. [Table: see text]

Evaluating antitumor activity and response determinants to trastuzumab deruxtecan in pediatric solid tumors.

10049 Background: Trastuzumab deruxtecan (T-DXd) is an anti-HER2 antibody-drug conjugate (ADC) linked to a topoisomerase inhibitor FDA-approved for several indications, including the treatment of HER2+ breast and gastric cancer. Although HER2 amplification is uncommon in pediatric cancers, recent demonstration of T-DXd efficacy in HER2-low breast cancer patients prompted us to examine the potential clinical relevance of T-DXd in pediatrics by evaluating HER2 expression and activity of T-DXd in preclinical pediatric solid tumor models. Methods: Cell viability was assessed in a panel of histologically diverse pediatric solid tumor cell lines and 2 HER2-amplified adult cancer cell lines treated with T-DXd, payload (DXd), and a control IgG-ADC. HER2 protein expression in patient-derived xenograft (PDX) tumors was evaluated by immunohistochemistry (IHC) using 5 clinically validated anti-HER2 antibodies. RNAseq was performed on clinical (n=290) and PDX (n=184) tumors to determine relative expression of ERBB2. In vivo activity of T-DXd was evaluated in osteosarcoma (OS, n=10), Wilms tumor (WT, n=1) and malignant rhabdoid tumor (MRT, n=1) PDX models and a desmoplastic small round cell tumor (DSRCT) cell line xenograft model. Differences in tumor volume and time to disease progression was assessed and compared across treatments and models. Responses were correlated with HER2 expression by IHC. Results: In vitro, HER2-amplified control cell lines demonstrated a &gt;30-fold reduction of IC50 when comparing T-DXd to ADC control. In contrast, the ADC control IC50 was nearly identical to T-DXd across all pediatric cancer cell lines, consistent with the absence of HER2 amplification in these models. We observed focal and membranous staining of HER2 by IHC in PDXs but was quite variable across antibodies tested: WT 0-17% HER2+ cases (n=6), MRT 0-40% (n=5), DSRCT 0-33% (n=24), OS 0-7% (n=30). ERBB2 gene expression was highest in DSRCT followed by WT, OS and MRT. In vivo efficacy studies demonstrated complete and partial responses in OS, WT, and DSRCT and improved disease control rates (OS: 67%, p=0.006, Mann-Whitney; WT: 100%; DSRCT: 100%). However, T-DXd and ADC control demonstrated similar activity in all tumor types with no consistent correlation between in vivo response and HER2 expression. Consistent with these preclinical studies, 4 patients with progressive DSRCT were treated with T-DXd via compassionate/off-label access with signs of clinical and radiographic responses. Conclusions: T-DXd shows significant preclinical antitumor activity across multiple pediatric solid tumors but little correlation with HER2 expression suggesting a mechanism of action similar to the clinical activity observed in HER2-low breast cancer. Xenograft efficacy studies and preliminary clinical experience with T-DXd in DSRCT patients warrant formal clinical trial investigation in this largely incurable disease.

Clinical features and outcomes of patients with breast cancer with leptomeningeal carcinomatosis.

e13162 Background: Leptomeningeal carcinomatosis (LMC) is a rare, but deadly complication in breast cancer, with prior studies showing median overall survival (OS) of 15 weeks. There is a paucity of data on histologic and receptor subtype-specific survival, and there is no standard of care currently for treatment of LMC in breast cancer. We reviewed the outcomes of a contemporary cohort of breast cancer patients (pts) with LMC. Methods: This is a single-institution retrospective analysis of 38 female breast cancer pts diagnosed with LMC between 2016-2023, based on radiographic features and/or positive cerebrospinal fluid (CSF) cytology or CSF circulating tumor cells (CTCs). Patients consented to share information with a research biorepository, and we conducted a chart review of their clinical features and OS with LMC. Results: 25 pts (65.8%) had invasive ductal carcinoma (IDC), 7 pts (18.4%) had invasive lobular carcinoma (ILC), 4 (10.5%) had metaplastic carcinoma, and 2 (5.3%) had mixed IDC/ILC. 22 pts (57.9%) had triple-negative breast cancer (TNBC), 12 (31.6%) had estrogen receptor positive (ER+)/human epidermal growth factor receptor 2 negative (HER2-), and 4 (10.5%) had HER2+ disease. Median age at LMC diagnosis was 50 years. Median time between Stage IV and LMC diagnosis was 11 months. Pts received a median of 2 lines of systemic therapy for metastatic disease prior to LMC diagnosis. 11 pts (28.9%) had parenchymal brain metastasis prior to LMC diagnosis. 32 pts (84.2%) had signs of LMC on Magnetic Resonance Imaging of the brain and/or spine at diagnosis. 25 pts underwent CSF cytology and 13 pts underwent CSF CTC evaluation at LMC diagnosis; 14/25 pts (56%) had positive CSF cytology and 10/13 pts (76.9%) had detectable CSF CTCs. 21 pts (55.3%) underwent whole-brain radiotherapy, and 2 pts (5.3%) received proton craniospinal irradiation. 21 pts (55.3%) received IT therapy. 27 pts (71.1%) received at least 1 line of systemic therapy post-LMC diagnosis. Median OS between LMC diagnosis and death or last oncology follow up for the entire cohort was 5 months (range 0-57 months, 95% CI 3.0-8.0). There was a significant difference in median OS with LMC by receptor subtype: TNBC 3.5 months, ER+/HER2- 8 months, and HER2+ 23 months (p=0.0047). Two HER2+ pts survived ≥ 3 years post-LMC diagnosis with anti-HER2 antibody-drug conjugates and tyrosine kinase inhibitors +/- stereotactic radiosurgery (SRS) to parenchymal brain metastases. Amongst 9 pts with ER+/HER2-low disease, longer survival with LMC (≥ 16 months) was observed with trastuzumab deruxtecan, IT topotecan +/- IT trastuzumab, and SRS to parenchymal brain metastases. Conclusions: This study highlights heterogeneity in outcomes amongst breast cancer pts with LMC by receptor subtype, as well as improvement in outcomes for selected pts treated with novel therapeutics and a multidisciplinary approach. Larger prospective studies are needed to inform treatment paradigms for LMC.