HER2-targeted Antibody Research Articles

HER2(-low)-Expression on Circulating Tumor Cells (CTCs) and corresponding Metastatic Tissue in Metastatic Breast Cancer (MBC).

Significant progress has been made in the targeted therapy of metastatic breast cancer (mBC) in recent years. In this context, new biomarkers enable personalized therapy management and individualized therapy monitoring. Therefore, the systemic treatment is based increasingly on the biological characteristics of the tumor disease. Given the challenges of obtaining fresh tumor tissue through biopsies, the significance of liquid biopsies for assessing circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) is of growing importance for the detection of prognostic and predictive biomarkers. Multiple studies have shown that the number of CTCs decreases under therapy, especially under anti-HER2-targeted therapy, and that the expression of the HER2 status on CTCs could play a role in predicting therapy response and therapeutic monitoring. The aim of this study was to analyze the HER2 status of CTCs in mBC patients before and after 3 months of systemic therapy to evaluate changes in the number of HER2 positive CTCs. The study focuses on HER2-low, which plays an increasingly important role in clinical practice due to new developments of HER2 targeting antibody drug conjugates (ADCs). In this context, temporal and spatial heterogeneity of the disease represent a major diagnostic challenge. A total of 324 patients with complete immunohistochemistry (IHC) of biopsied metastases were divided into five groups: HER2 negative (-)/hormone receptor (HR) negative (-), HER2 -/HR positive (+), HER2 +/HR +/-, HER2-low/ HR + and HER2-low/ HR -. Before and after 3 months of a new therapeutic line for mBC, CTCs were enumerated and analyzed for HER2 expression using the Cell-Search® system. Overall survival of all subgroups was calculated. The analyses revealed a discrepancy between the HER2 status of CTCs and corresponding tumor tissues in 98 patients (30.2%). The number of CTCs in general and the number of HER2 + CTCs decreased during systemic treatment, mainly in HER2 + tumors, but also in the other subgroups. Discrepancy in the HER2 status of the metastases and of CTCs was observed in approximately one third of patients. Measuring HER2 on CTCs could potentially offer a means to longitudinally monitor HER2 status during therapy and simultaneously address challenges such as tumor heterogeneity. Therefore, the predictive value of HER2 on CTCs should be further investigated in clinical trials.

Resistance mechanisms and prospects of trastuzumab

Breast cancer that overexpresses Human Epidermal Growth Factor Receptor 2 (HER2+) due to gene amplification or overexpression constitutes 15-20% of all breast cancer cases. Trastuzumab, the first FDA-approved monoclonal antibody targeting HER2, serves as the standard first-line treatment for HER2-positive advanced breast cancer, as recommended by multiple clinical guidelines.Currently, accumulated clinical evidence reveals a considerable degree of variability in the response of HER2+ breast cancer to trastuzumab treatment. Specifically, over 50% of patients either do not respond to or develop resistance against trastuzumab.The specific mechanisms of resistance to trastuzumab are currently unclear. This paper aims to review the existing research on the resistance mechanisms of trastuzumab, based on its target, from aspects such as genetic loci, molecular structure, signaling pathways, and the tumor microenvironment and to outline current research progress and new strategies.

Switching to a Fixed-dose Combined Pertuzumab and Trastuzumab With Recombinant Human Hyaluronidase Subcutaneous Injection to Treat Human Epidermal Growth Factor Receptor 2-positive Breast Cancer in Real-world UK Clinical Practice

Current standard of care for human epidermal growth factor receptor 2 (HER2)–positive breast cancer is first-line treatment with chemotherapy in combination with the HER2-targeting monoclonal antibodies, trastuzumab and pertuzumab. While this treatment approach is associated with improved clinical outcomes, there is a treatment burden associated with the invasive and time-consuming nature of separate intravenous (IV) administration of pertuzumab and trastuzumab. In 2020, a novel subcutaneous (SC) formulation of pertuzumab plus trastuzumab with recombinant human hyaluronidase, available as a fixed-dose combination vial that can be administered in 5–8 minutes, was approved for use by the US Food and Drug Administration and the European Medicines Agency. AimA UK cancer centre set out to switch all patients currently receiving IV infusion of pertuzumab and trastuzumab over to the combined SC injection in a safe and timely manner and to initiate all future patients on the combined SC injection. Materials and methodsOrganisational governance approval was obtained before a novel project model approach was used to implement the treatment switch which incorporated aspects such as education and multidisciplinary team collaboration. ResultsOf the 97 eligible patients, 99% were switched to the combined SC injection safely and effectively over a 4-week period. Between 1st April 2021 and 30th September 2022, 3062 hours of pharmacy aseptic preparation time and 6764 hours of day unit chair time were saved. The number of aseptic unit operation days above the maximum capacity was reduced post-switch. ConclusionThis initiative demonstrated the ability to rapidly and effectively transition >95% of eligible breast cancer patients from separate IV trastuzumab and pertuzumab to a fixed combined SC formulation. Patient benefits included shorter administration appointments and a less invasive form of treatment, whereas healthcare system benefits included substantial savings in aseptic preparation time and chair time, and a meaningful increase in clinic capacity. The reported treatment-switch process provides a model that can be adopted by other centres wishing to implement similar treatment switches.

Race/ethnicity and human epidermal growth hormone receptor 2–targeted therapy for breast cancer.

91 Background: Breast cancer is the most common cancer in the US. Up to 25% of breast cancers are classified as human epidermal growth factor receptor 2 (HER2)-positive and associated with an aggressive tumor burden. HER2-targeting monoclonal antibodies improves survival in patients with HER2-positive breast cancer. Prior work has demonstrated disparities in access to oncologic therapies among older women. Our study seeks to examine racial/ethnic disparities in receiving HER2-targeted therapies for patients with HER2-positive breast cancer and trends in use over time. Methods: In the Surveillance, Epidemiology and End Results (SEER) Medicare-linked database we identified women diagnosed with breast cancer from 2010 to 2019. We included those >66 years old who survived 12 months after diagnosis, were enrolled in Medicare Parts A/B for 12 months pre and post-diagnosis, and had local or regional stage HER2-positive cancer. Our primary outcome was receipt of HER2-targeted therapies in the 12 months after diagnosis. Our independent variable was race/ethnicity as measured by the validated Research Triangle Institute race/ethnicity codes in Medicare. Due to small sample sizes, we focus our analysis on White, Black, or Hispanic women. We used multivariable Modified Poisson regression to evaluate changes in the probability of HER2-targeted therapy receipt by race/ethnicity over time, adjusted for sociodemographics, cancer factors, and medical comorbidities. Results: Our cohort comprised 13,887 patients including 8.7% Black, 7.5% Hispanic, and 83.8% White (mean age 74.9). Overall, 7,351 (52.9%) received HER2-targeted therapies in the 12 months post-diagnosis, with use increasing over time in all racial/ethnic groups (Table). Compared with White patients, Black and Hispanic patients had a 19% (adjusted risk ratio [aRR] 0.81, 95% CI:0.69-0.96) and 27% (aRR 0.73, 95% CI 0.61-0.89) lower likelihood, respectively, of receiving HER2-targeted therapies from 2010-2011 (Table). By 2018-2019, no significant differences in receiving HER2-targeted therapies were observed across racial/ethnic groups. Conclusions: In a national cohort of Medicare enrollees with HER2-positive breast cancer, we observed significant racial/ethnic disparities which narrowed over time. Overall utilization rates were low. Future work is needed to understand how improved access to breast cancer treatments impact downstream outcomes. Use of human epidermal growth hormone receptor 2–targeted therapy from 2010-2011 and 2018-2019 by race/ethnicity. Race and Ethnicity Unadjusted Rates Adjusted Risk Ratios (95% CI)* 2010-2011 2018-2019 2010-2011 2018-2019 Black 36% 62% 0.81 (0.69-0.96) 0.97 (0.87-1.08) Hispanic 31% 68% 0.73 (0.61-0.89) 1.01 (0.92-1.12) White 42% 64% Reference Reference *Adjusted for age, marital status, region, breast cancer stage and year of diagnosis, and medical comorbidities.

Analysis of HER2-Low Breast Cancer in Aotearoa New Zealand: A Nationwide Retrospective Cohort Study.

To perform the first national analysis of demographic and clinicopathological features associated with the HER2 positive, HER2-low, and HER2-zero invasive breast cancers in New Zealand. The study will reveal the proportion of women who may benefit from new HER2-targeted antibody drug conjugate (ADC) therapies. Utilising data from Te Rēhita Mate Ūtaetae (Breast Cancer Foundation NZ National Register), the study analysed data from women diagnosed with invasive breast cancer over a 21-year period. The HER2 status of tumours was classified into three categories-HER2-zero, HER2-low, HER2-positive. From 2009-2021, 94% of women underwent HER2 testing, with 14% diagnosed with HER2-positive breast cancer. For advanced-stage disease, 38% of those formerly classified as HER2-negative were reclassified as HER2-low. Including HER2-positive breast cancers, this indicates that 60% of women with advanced breast cancer may potentially benefit from the new HER2-directed ADCs (approximately 120 women per year). The findings suggest a significant proportion of women with invasive breast cancer in New Zealand could benefit from new HER2-targeted treatments. There is a need to standardise HER2 testing to enhance personalised treatment and improve outcomes.

Optimization of a pendant-shaped PEGylated linker for antibody-drug conjugates

In this work, we conceived and developed antibody-drug conjugates (ADCs) that could efficiently release the drug after enzymatic cleavage of the linker moiety by tumoral proteases. The antibody-drug linkers we used are the result of a rational optimization of a previously reported PEGylated linker, PUREBRIGHT® MA-P12-PS, which showed excellent drug loading capacities but lacked an inbuilt drug discharge mechanism, thus limiting the potency of the resulting ADCs. To address this limitation, we chose to incorporate a protease-sensitive trigger into the linker to favor the release of a “PEGless” drug inside the tumor cells and, therefore, obtain potent ADCs. Currently, most marketed ADCs are based on the Val-Cit dipeptide followed by a self-immolative spacer for releasing the drug in its unmodified form. Here, we selected two untraditional peptide sequences, a Phe-Gly dipeptide and a Val-Ala-Gly tripeptide and placed one or the other in between the drug on one side (N-terminus) and the rest of the linker, including the PEG moiety, on the other side (C-terminus), without a self-immolative group. We found that both linkers responded to cathepsin B, a reference lysosomal enzyme, and liberated a PEG-free drug catabolite, as desired. We then used the two linkers to generate ADCs based on trastuzumab (a HER2-targeting antibody) and DM1 (a microtubule-targeted cytotoxic agent) with an average drug-to-antibody ratio (DAR) of 4 or 8. The ADCs showed restored cytotoxicity in vitro, which was proportional to the DM1 loading and generally higher for the ADCs bearing Val-Ala-Gly in their structure. In an ovarian cancer mouse model, the DAR 8 ADC based on Val-Ala-Gly behaved better than Kadcyla® (an approved ADC of DAR 3.5 used as control throughout this study), leading to a higher tumor volume reduction and more prolonged median survival.Taken together, our results depict a successful linker optimization process and encourage the application of the Val-Ala-Gly tripeptide as an alternative to other existing protease-sensitive triggers for ADCs.

The DNA repair pathway as a therapeutic target to synergize with trastuzumab deruxtecan in HER2-targeted antibody–drug conjugate–resistant HER2-overexpressing breast cancer

BackgroundAnti-HER2 therapies, including the HER2 antibody–drug conjugates (ADCs) trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd), have led to improved survival outcomes in patients with HER2-overexpressing (HER2+) metastatic breast cancer. However, intrinsic or acquired resistance to anti-HER2–based therapies remains a clinical challenge in these patients, as there is no standard of care following disease progression. The purpose of this study was to elucidate the mechanisms of resistance to T-DM1 and T-DXd in HER2+ BC patients and preclinical models and identify targets whose inhibition enhances the antitumor activity of T-DXd in HER2-directed ADC-resistant HER2+ breast cancer in vitro and in vivo.MethodsTargeted DNA and whole transcriptome sequencing were performed in breast cancer patient tissue samples to investigate genetic aberrations that arose after anti-HER2 therapy. We generated T-DM1 and T-DXd–resistant HER2+ breast cancer cell lines. To elucidate their resistance mechanisms and to identify potential synergistic kinase targets for enhancing the efficacy of T-DXd, we used fluorescence in situ hybridization, droplet digital PCR, Western blotting, whole-genome sequencing, cDNA microarray, and synthetic lethal kinome RNA interference screening. In addition, cell viability, colony formation, and xenograft assays were used to determine the synergistic antitumor effect of T-DXd combinations.ResultsWe found reduced HER2 expression in patients and amplified DNA repair–related genes in patients after anti-HER2 therapy. Reduced ERBB2 gene amplification in HER2-directed ADC–resistant HER2+ breast cancer cell lines was through DNA damage and epigenetic mechanisms. In HER2-directed ADC–resistant HER2+ breast cancer cell lines, our non-biased RNA interference screening identified the DNA repair pathway as a potential target within the canonical pathways to enhance the efficacy of T-DXd. We validated that the combination of T-DXd with ataxia telangiectasia and Rad3-related inhibitor, elimusertib, led to significant breast cancer cell death in vitro (P < 0.01) and in vivo (P < 0.01) compared to single agents.ConclusionsThe DNA repair pathways contribute to HER2-directed ADC resistance. Our data justify exploring the combination treatment of T-DXd with DNA repair–targeting drugs to treat HER2-directed ADC–resistant HER2+ breast cancer in clinical trials.

Dual targeting non-overlapping epitopes in HER2 domain IV substantially enhanced HER2/HER2 homodimers and HER2/EGFR heterodimers internalization leading to potent antitumor activity in HER2-positive human gastric cancer

BackgroundTrastuzumab and pertuzumab combination has been approved for the treatment of patients with HER2-positive metastatic breast cancer. However, trastuzumab and pertuzumab combination did not show improvement in overall survival in patients with HER2-positive metastatic gastric cancer.MethodsWe developed a new HER2-targeted monoclonal antibody, HLX22, targeting HER2 subdomain IV as trastuzumab but with non-overlapping epitopes. We examined the antitumor effects of this novel HER2-antibody in gastric cell lines and cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models.ResultsHLX22 in combination with HLX02 (trastuzumab biosimilar) induced enhancement of HER2/HER2 homodimers and HER2/EGFR heterodimers internalization, which ultimately led to the reduction in signal transductions involving STAT3, P70 S6, and AKT; gene expressions of FGF-FGFR-PI3K-MTOR, EGF-EGFR-RAS, TGF-β-SMAD, PLCG and cell cycle progression related pathways that favor tumor development, proliferation, progression, migration and survival in gastric cancer cell line NCI-N87 were also reduced. These differing but complementary actions contributed to the synergistic antitumor efficacy of the HLX22 and HLX02 combination in gastric cancer cell lines, CDX and PDX. In addition, HLX22 in combination with HLX02 demonstrated stronger antitumor efficacy than HLX02 and HLX11 (a potential pertuzumab biosimilar) combination treatment both in vitro and in vivo.ConclusionsThese results suggested that the application of non-competing antibodies HLX22 and HLX02 targeting HER2 subdomain IV together may be of substantial benefit to gastric cancer patients who currently respond suboptimal to trastuzumab therapy.

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.

InVivo PET Imaging of 89Zr-Labeled Natural Killer Cells and the Modulating Effects of a Therapeutic Antibody.

Natural killer (NK) cells can kill cancer cells via antibody-dependent cell-mediated cytotoxicity (ADCC): a tumor-associated IgG antibody binds to the Fcγ receptor CD16 on NK cells via the antibody Fc region and activates the cytotoxic functions of the NK cell. Here, we used PET imaging to assess NK cell migration to human epidermal growth factor receptor 2 (HER2)-positive HCC1954 breast tumors, examining the influence of HER2-targeted trastuzumab antibody treatment on NK cell tumor accumulation. Methods: Human NK cells from healthy donors were expanded ex vivo and labeled with [89Zr]Zr-oxine. In vitro experiments compared the phenotypic markers, viability, proliferation, migration, degranulation, and ADCC behaviors of both labeled (89Zr-NK) and unlabeled NK cells. Female mice bearing orthotopic human breast HCC1954 tumors were administered 89Zr-NK cells alongside trastuzumab treatment or a sham treatment and then scanned using PET/CT imaging over 7 d. Flow cytometry and γ-counting were used to analyze the presence of 89Zr-NK cells in liver and spleen tissues. Results: 89Zr cell radiolabeling yields measured 42.2% ± 8.0%. At an average specific activity of 16.7 ± 4.7 kBq/106 cells, 89Zr-NK cells retained phenotypic and functional characteristics including CD56 and CD16 expression, viability, migration, degranulation, and ADCC capabilities. In vivo PET/CT studies indicated predominant accumulation of 89Zr-NK cells in the liver and spleen. Ex vivo analyses of liver and spleen tissues indicated that the administered human 89Zr-NK cells retained their radioactivity invivo and that 89Zr did not transfer to cells of murine soft tissues, thus validating this 89Zr PET method for NK cell tracking. Notably, 89Zr-NK cells migrated to HER2-positive tumors, both with and without trastuzumab treatment. Trastuzumab treatment was associated with an increased 89Zr-NK cell signal at days 1 and 3 after injection. Conclusion: In vitro, 89Zr-NK cells maintained key cellular and cytotoxic functions. In vivo, 89Zr-NK cells trafficked to HER2-postive tumors, with trastuzumab treatment correlating with enhanced 89Zr-NK infiltration. This study demonstrates the feasibility of using PET to image 89Zr-NK cell infiltration into solid tumors.

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.

Surface-Available HER2 Levels Alone Are Not Indicative of Cell Response to HER2-Targeted Antibody-Drug Conjugate Therapies.

HER2-targeting therapies have advanced breast cancer treatment over the past decade. Clinically, eligibility for HER2 therapies is determined by assessing HER2 levels on tumor cell surfaces through immunohistochemistry or by gene regulation through fluorescence in situ hybridization. HER2 therapies are not always effective in patients with elevated levels of HER2, questioning whether the amount of HER2 is sufficiently predictive of patient outcomes. Additionally, the HER2-targeting antibody-drug conjugate (ADC) Enhertu® was recently approved for metastasized HER2-low cancers, confirming the benefits of HER2 treatment for patients with low HER2 levels. To evaluate the correlation between HER2 levels and treatment efficacy, we quantified HER2 on eight cell lines using flow cytometry while simultaneously determining the toxicity of two HER2-targeting ADCs. Both HER2-high cell lines and HER2-low cell lines had significant toxicity responses to ADCs. We quantified HER2 internalization and found no correlation between HER2 levels and the percentage of internalization. We found a useful metric suggesting that a minimum number of HER2 receptors trafficked to lysosomes is sufficient to provide effective treatment. Our results indicate that the current standards of determining eligibility for HER2 therapy could limit patients' access to effective treatment. In conclusion, HER2 levels are not wholly adequate to determine the response to ADC treatment.

Preliminary safety and efficacy of TQB2930, a HER2-targeted bispecific antibody in patients with advanced breast cancer: Results from a phase 1b study.

1026 Background: TQB2930 is a HER2-targeted bispecific antibody, binding to two distinct HER2 epitopes, the same domain as trastuzumab (ECD4) and pertuzumab (ECD2). This study aims to evaluate the safety and efficacy of TQB2930 for patients with advanced breast cancer after failure of standard therapy. Methods: This phase 1b, dose-escalation and expansion trial included patients preferred HER2-expressing or HER2-amplified breast cancer who had received standard therapy. In the dose-escalation phase, TQB2930 was given weekly (10mg/kg, QW), biweekly (20mg/kg, Q2W), or triweekly (30mg/kg, Q3W). After the dose-escalation phase, eligible patients were enrolled and dosed biweekly or triweekly in the expansion cohort. The primary endpoints were safety, maximum tolerated or maximum administered dose, and the secondary endpoints were immunogenicity, pharmacokinetics, and tumor response per RECIST v1.1. Results: As of Dec 20, 2023, 34 patients(pts) have received TQB2930 weekly (n=3), biweekly (n=16), and triweekly (n=15). All pts were female, the median age was 59. 22 pts had HER2 expression of ICH3+ or ICH2+ with FISH+, and the others had ICH2+ with FISH- or ICH1+. The median prior lines of therapies were 3 (range: 0-8), with one pt intolerance to first-line treatment enrolled, and the median prior lines of HER2-targeted therapies were 2 (range: 0-8). No dose-limited toxicity was observed. The main treatment-related adverse events (TRAEs) were infusion reaction, occult blood of urine, leukopenia, and neutropenia. 3 pts were reported grade≥3 TRAEs, including neutropenia, anemia, and hypokalemia. Of 31 response-evaluable pts, the objective response rate (ORR) was 25.8% with 8 partial responses (PRs) were observed (including 5 confirmed PRs and 3 PRs awaiting confirmation). The disease control rate was 80.6%. Moreover, 5 pts achieved PR at 30mg/kg (ORR 41.7%), including one with prior exposure to trastuzumab, pyrotinib, tucatinib, ARX788, and the other one prior to trastuzumab, pertuzumab, lapatinib, MRG002. The median progression-free survival for all pts was 5.5 months (95%CI 3.58-NE). Additionally, Pharmacokinetic analysis showed exposure (Cmax and AUC0-t) of TQB2930 increased linearly with doses within 10~30mg/kg. After dosing, the mean peak concentration reached at 2.5-4.3 h, and the elimination half-life of TQB2930 was 109-161 h. Conclusions: TQB2930 is well tolerated and has demonstrated promising single-agent anti-tumor activity in HER2-positive breast cancer who have failed standard anti-HER2 therapies, including multiple lines of prior HER2 targeted agents. These early signs of activity support the further exploration of combination therapy of TQB2930 and the study is ongoing. Clinical trial information: NCT06202261 .

Heterogeneity of immune status in patient-derived malignant pleural effusion and ascites: Relationship to the ex-vivo efficacy of a HER2-targeted tri-specific antibody and a novel cytokine fusion protein.

Heterogeneity of immune status in patient-derived malignant pleural effusion and ascites: Relationship to the ex-vivo efficacy of a HER2-targeted tri-specific antibody and a novel cytokine fusion protein.

Zanidatamab in previously-treated HER2-positive (HER2+) biliary tract cancer (BTC): Overall survival (OS) and longer follow-up from the phase 2b HERIZON-BTC-01 study.

4091 Background: For patients with BTC that has progressed after first-line therapy, prognosis is poor with a median OS of 6-9 months with subsequent chemotherapy. Zanidatamab is a HER2-targeted bispecific antibody that binds to two non-overlapping HER2 domains and crosslinks neighboring HER2 proteins. In the primary analysis of the phase 2b HERIZON-BTC-01 trial, after a median follow-up of 12.4 months (data cutoff: October 10, 2022), zanidatamab showed encouraging antitumor activity (41% confirmed objective response rate [cORR]) with rapid and durable responses and a manageable safety profile in patients with previously treated HER2+ BTC. OS data were immature at that time. Here, we report updated analyses, including OS. Methods: HERIZON-BTC-01 (NCT04466891) is an ongoing phase 2b trial assessing zanidatamab (20 mg/kg IV Q2W) in patients with HER2/ERBB2 gene amplification and immunohistochemistry (IHC) 2+ or 3+ (Cohort 1; HER2+); or 0 or 1+ (Cohort 2) locally advanced, unresectable, or metastatic BTC (gallbladder cancer, intra/extrahepatic cholangiocarcinoma) who received prior gemcitabine-containing treatment. The primary endpoint was cORR. Select secondary endpoints included duration of response (DoR), OS, and frequency and severity of adverse events (AEs). Updated efficacy analyses include only Cohort 1; safety analyses include Cohorts 1 and 2. Results: As of the data cutoff (July 28, 2023), median (range) follow-up was 21.9 (16-34) months. In the 80 patients in Cohort 1 (HER2+), treatment was ongoing for 9 (11%) patients and 20 (25%) patients remained on the study. cORR was unchanged from the primary analysis (n = 33; 41%) with 1 additional complete response (n = 2; 2.5%). The median DoR (95% CI) increased approximately 2 months to 14.9 (7.4, not reached) months. Median OS (95% CI) was 15.5 (10.4, 18.5) months; 12-month OS (95% CI) was 56.2% (44.3, 66.5). Among all 87 patients (Cohort 1 and Cohort 2), 18 (21%) experienced grade ≥3 treatment-related AEs (TRAEs). The most common grade 3 TRAEs (occurring in &gt; 2 patients) were diarrhea (4 [5%]); anemia (3 [3%]), and ejection fraction decreased (3 [3%]). Only one patient had a grade 4 TRAE (aspartate aminotransferase increased). There were no deaths due to TRAEs. Serious AEs occurred in 8 (9%) patients; 2 (2%) patients discontinued treatment due to an AE (pneumonitis and ejection fraction decreased; 1 patient each). Conclusions: With close to 2 years of median follow-up, zanidatamab demonstrated a median OS of 15.5 months and a median duration of response of 14.9 months (an increase compared with the initial report) in previously-treated patients with HER2+ BTC; a patient population with significant unmet need. With additional follow-up, safety remained manageable. A phase 3 trial of zanidatamab in the first-line setting for patients with metastatic BTC is planned. Clinical trial information: NCT04466891 .

Neoadjuvant pyrotinib and inetetamab in combination with chemotherapy for locally advanced HER2-positive breast cancer (NeoPICD study): A prospective, multicenter, open-label, single-arm study.

e12627 Background: Inetetamab, a novel monoclonal antibody targeting HER2, alters the Fc region amino acids, which induces ADCC stronger than trastuzumab. Pyrotinib is a small chemical inhibitor of pan-HER receptor tyrosine kinase. The globally recommended first-line neoadjuvant treatment for HER2-positive breast cancer is chemotherapy and two large-molecule monoclonal antibodies, which have unsatisfactory benefits for 50% of patients. This study aims to investigate the effectiveness and safety of targeted medicines, specifically inetetamab and pyrotinib, in conjunction with chemotherapy for patients diagnosed with locally advanced HER2-positive breast cancer. Methods: The trial was structured as a multicenter, open-label, single-arm, prospective study. 143 treatment-naive HER2-positive locally advanced breast cancer patients were planned for the trial. Eligible patients will be administered six cycles of neoadjuvant treatment, including carboplatin (AUC=6mg/mL×min, ivgtt), doxorubicin (75mg/m2, ivgtt), inetetamab (initial loading dosage of 8mg/kg, maintenance dose of 6mg/kg), and pyrotinib (400mg/day, po). The surgery was conducted after the neoadjuvant phase, subsequent to a one-year course of targeted therapy with inetetamab and pyrotinib. The primary endpoint of the study is the total pathologic complete response (tpCR). The secondary endpoints include event-free survival (EFS), disease-free survival (DFS), distant metastasis-free survival (DMFS), neurologic disease-free survival (NDFS), overall survival (OS), and safety. Results: A cohort of 70 patients was enrolled between Nov. 27, 2021 and Feb. 1, 2024. Most patients completed the six-cycle neoadjuvant therapy with inetetamab, pyrotinib, and chemotherapy. The pathological findings of 49 patients who had radical surgery revealed that 65.3% (32/49, 95% CI, 0.515-0.791) of them achieved tpCR (ypT0/Tis ypN0). The initial subgroup analysis revealed that among patients with negative hormone receptors, the rate of tpCR was 80.0% (24/30, 95% CI, 64.8-95.2). Moreover, hormone receptor was statistically determined to be an independent factor influencing the effectiveness of the new treatment regimen ( p=0.032). The prevailing grade 3 or more severe adverse events included anemia (12.8%), diarrhea (10.0%), leukopenia (4.2%), liver dysfunction (4.2%) and renal dysfunction (4.2%). As of now, no treatment-related deaths have been documented. Conclusions: The ongoing study is actively enrolling participants. Preliminary findings from the study indicate that the combination of neoadjuvant inetetamab and pyrotinib with chemotherapy has demonstrated satisfactory effectiveness and manageable side effects. This offers a promising alternative for patients with locally advanced breast cancer that is HER2-positive. Clinical trial information: NCT06234137 .

An open-label, multicenter, phase 2 study to evaluate the safety and efficacy of BB-1701, a novel antibody drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER2), in previously treated patients with HER2-positive (HER2+) or HER2-low unresectable or metastatic breast cancer (BC).

TPS1122 Background: Treatment options for patients (pts) with unresectable or metastatic BC have improved with the development of novel targeted therapies including trastuzumab deruxtecan (T-DXd), an ADC directed against HER2 with a cytotoxic topoisomerase I inhibitor as a payload. Currently, there are limited treatment options for pts with HER2+ or HER2-low metastatic BC that has progressed on T-DXd. BB-1701 is an ADC consisting of a monoclonal antibody targeting HER2 with eribulin (microtubule inhibitor) as a payload that is capable of exerting a bystander effect. A first-in-human dose-finding Study 101 of BB-1701 is ongoing. Here we describe Study 205, an open label, multicenter, phase 2 study of BB-1701 in pts with HER2+ or HER2-low unresectable or metastatic BC who have disease progression after treatment with T-DXd. Methods: Study 205 (NCT06188559) includes dose-optimization and dose-expansion parts for BB-1701. Eligible pts must have histologically confirmed HER2+ or HER2-low, unresectable or metastatic BC, with measurable disease per RECIST v1.1. Prior treatment must include 1–3 prior chemotherapy-based regimens for unresectable or metastatic BC, including T-DXd. The primary objectives of the dose-optimization part include determining the recommended dose (RD) and evaluating safety and tolerability of BB-1701. The RD will be assessed by randomly assigning ~50 pts into 1 of 3 dosing cohorts (1.6 mg/kg on day 1 Q3W, 0.8 mg/kg on days 1 and 8 Q3W, and 1.2 mg/kg on day 1 Q3W; IV) in a 2:2:1 ratio. Randomization will be stratified by HER2 status (HER2+ vs. HER2-low) documented prior to T-DXd treatment. The dose-expansion part will enroll ~85 pts at RD; the primary objective includes evaluating the efficacy of BB-1701 at the RD. In both study parts, secondary objectives include assessment of additional efficacy measures (i.e., duration of response [DOR], progression free survival [PFS], overall survival [OS], disease control rate [DCR], clinical benefit rate [CBR], and time to response [TTR]), and pharmacokinetics. Efficacy endpoints will be assessed per RECIST v1.1 by the investigator during the dose-optimization part or by Blinded Independent Central Review during the dose-expansion part. Safety assessments will consist of recording, monitoring, and grading of adverse events (AEs) based on CTCAE v5.0, AEs of special interest, and serious AEs. In both study parts, exploratory objectives will include evaluation of biomarkers of response to BB-1701 and BB-1701 immunogenicity; other efficacy measures (i.e., PFS on the next line of therapy) and population pharmacokinetics will be analyzed in the dose-expansion part only. Pt enrollment is currently open. Clinical trial information: NCT06188559 .

HER2 expression-independent antitumor effect of trastuzumab deruxtecan (T-DXd) on pediatric solid tumors.

e15016 Background: Treatment of pediatric solid tumors shows limited improvement even with intensification of conventional chemotherapy, suggesting novel approaches such as targeted therapies are needed. Trastuzumab Deruxtecan (T-DXd), a HER2-targeting antibody–drug conjugate, exhibits significant anti-cancer activity in breast cancers with a broad range of HER2 expression. T-DXd might be a promising agent for refractory or relapsed pediatric solid tumors, but its efficacy in pediatric tumors needs to be studied. Methods: Anti-cancer efficacy of T-DXd and its payload DXd were assessed in vitro by utilizing our in-house cancer cell line models. Cytotoxicity assays were performed for 60 pediatric cancer cell lines, including Neuroblastoma (NB) = 25, Ewing sarcoma / Ewing sarcoma family of tumors (EWS / EWSFT) = 17, Rhabdomyosarcoma (RMS) = 10, Others (Osteosarcoma, Brain tumor, Wilms tumor, Hepatoblastoma, and Malignant rhabdoid tumor (MRT) = 8, and 2 breast cancer cell lines expressing HER2 high or low (IHC score 2+ or 0) as positive or low control, respectively. We analyzed HER2 expression on the cell surface by flow cytometry and evaluated relative mean fluorescence intensity (MFI) values. Results: In the flow cytometric assessment, pediatric cancer cell lines showed smaller median MFI of 1.40 (0.67 - 2.71) compared with breast cancer control with HER2 high expression (33.77). The median MFI of each cell lines were 0.94 in NB, 1.76 in EWS / EWSFT, 1.42 in RMS, 1.52 in other pediatric cancers. Although low or no expression of HER2, certain inhibitory activities to the cell growth were observed for T-DXd against a part of NB, EWS, RMS and MRT cell lines, with the minimum IC50 values of 14.5 nM, 6.5 nM, 10.2 nM, 8.1 nM, respectively. In NB, EWS and RMS, a wide range of sensitivity to T-DXd were seen among different cell lines in the same disease. Most of cell lines showed high sensitivity to DXd (Median IC50 value: 0.90 nM [0.08 - 6.46 nM]), but, among them, cell lines with lower sensitivity to DXd tend to show less sensitivity to T-DXd. There was no clear correlation between sensitivity to T-DXd and HER2 expression among pediatric cancer cell lines, indicating that other mechanism such as intrinsic sensitivity to payload might affect antitumor activity of T-DXd. Conclusions: T-DXd exhibited antitumor efficacy against pediatric solid tumors in vitro irrespective of HER2 expression. Our results suggest that T-DXd might be an alternative therapy for pediatric solid tumor cases for whom conventional chemotherapies and other targeting therapies are ineffective. This study supports further investigation for T-DXd in this population.

Clinical significance of HER2 expression between primary tumors and metastatic lymph nodes in patients with extramammary Paget's disease.

e21568 Background: HER2 has been reported to be a potential oncogene and therapeutic target in extramammary Paget's disease (EMPD). However, the expression of HER2 in EMPD, especially in matched metastatic lymph nodes (LNs), is limited. Here, we investigated the heterogeneity of HER2 expression between primary tumors and positive nodes and its clinical significance in advanced EMPD patients and detected the efficacy of HER2-targeted antibody drug conjugates (ADCs) in EMPD. Methods: A total of 170 patients with pathologically confirmed EMPD of the scrotum and/or penis treated at SYSUCC from 2003 to 2023 were included. HER2 IHC staining (anti-HER2/neu (4B5), Ventana) and scoring were performed according to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2023 guidelines. Outcome relationships were explored using Cohen's kappa coefficient, multivariate Cox regression and log-rank analysis. Results: A total of 102 primary tumor and 32 metastatic specimens were ultimately subjected to HER2 IHC staining. HER2 high-expression (IHC: 2/3+) was detected in 71.6% (0: 9.8%, 1+: 18.6%, 2+: 40.2% and 3+: 31.4%) and 68.8% (0: 21.9%, 1+: 9.4%, 2+: 28.1% and 3+: 40.6%) of the primary tumors and metastatic LNs, respectively. HER2-high EMPD patients experienced poorer outcomes, with a 5-year OS of 56.5%, than did HER2-low patients (P = 0.032). A multivariate Cox regression model showed that a positive lymph node (HR 15.39, 95% CI 3.79~62.43; P &lt; 0.001) and HER2 high-expression in primary tumors (HR 3.68, 95% CI 1.49~9.09; P = 0.005) were independent poor prognostic factors. Notably, in 31 paired samples, 35.5% (n = 11) of patients had inconsistent HER2 expression between primary tumors and corresponding lymph node metastases. Six (19.4%) patients exhibited a shift from high expression of HER2 in primary tumors to low expression of HER2 in the lymph nodes, and 5 (16.1%) patients exhibited the reverse change. Advanced EMPD patients with HER2 high-expression were treated with Disitamab Vedotin (RC48), for which the ORR was 80% and the DCR was 100% (n = 5). No adverse events (AEs) above grade 3-4 were observed. Conclusions: HER2 was highly expressed in both primary and metastatic LNs in EMPD patients. However, there was some heterogeneity in HER2 expression between paired primary and corresponding metastatic LNs. The expression status of HER2 should be evaluated in both primary tumors and corresponding lymph node metastases. A positive lymph node and HER2 high-expression are poor prognostic factors in patients with EMPD. RC48 demonstrated significant efficacy in treating patients with HER2-high advanced EMPD and has promising potential that requires further validation.

Abstract PO1-29-02: Two and a half years follow-up data of HER2-targeted bispecific antibody KN026 combined with docetaxel as first-line treatment for HER2-positive recurrent/metastatic breast cancer

Abstract Background: KN026 is a novel bispecific HER2-targeted antibody. Fully humanized, IgG1-like antibody binds to two distinct HER2 epitopes, the same domains as trastuzumab and pertuzumab. Preliminary safety and efficacy results (data as of Aug 18, 2022) were presented at SABCs 2022(PD18-08), showed promising efficacy and tolerability. Herein, we update the 2.5-year follow-up results. Methods: Eligible subjects with recurrent/metastatic breast cancer, HER-2 positive and treatment-naive were enrolled. Subjects received KN026 30 mg/kg combined with docetaxel 75 mg/m2 Q3W until disease progression, unacceptable toxicity, or other reasons. The primary endpoints were ORR and DoR. The secondary endpoints included safety, PFS and OS. Results: As of data cut-off date (Sep 15, 2023), 57 subjects were enrolled, the median age was 52 years (min:30, max:67), 100% were female, and 91.2 % (52/57) were stage IV. There were 34 and 23 subjects with and without visceral metastasis, respectively. 48 subjects with high HER2 expression (IHC 3+), and the other 9 subjects with HER2 expression 2+ or 1+. The confirmed ORR within 55 evaluable subjects was 76.4% (42/55). The DoR was not reached yet with a median follow-up of 27.0 mons (95% CI: 26.28, 28.98). The median study follow-up was 30.6 mons (95% CI: 29.11, 31.77). The mPFS was 27.7 mons (95% CI:17.97, NE) and the mOS was not reached. The OS rates at 12m, 24m and 30m were 93.0% (95% CI: 82.37, 97.31), 84.2% (95% CI: 71.85, 91.45) and 78.5% (95% CI: 65.25, 87.21). The mPFS of subjects with or without visceral metastasis were 23.6 mons and not reached. The mPFS of subjects with or without brain metastasis were 13.7 mons and 28.1 mons, respectively. The mPFS of 48 subjects with high HER2 expression (3+) was 28.1 months. The incidence of KN026-related Grade≥3 TRAE was 43.9% (25/57), including neutrophil count decreased 24.6% (14/57), white blood cell count decreased 12.3% (7/57), hypokalaemia 7.0% (4/57), diarrhoea 3.5% (2/57) and others less than 2%. The incidence of serious adverse events related to KN026 was 12.3% (7/57). There was no KN026 -related death. Conclusions: KN026 in combination with docetaxel is well tolerated and has shown promising clinical benefit as 1L treatment for HER2-positive BC. After 2.5 years follow-up, mPFS was 27.7 mons and the 24-months OS rate was 84.2%, which is very promising. No new safety signals were observed. Robustness of efficacy and safety results will be further confirmed in an ongoing randomized phase 3 clinical trial with PTH as control. Citation Format: Qingyuan Zhang, Jingxuan Wang, Quchang Ouyang, Xiaojia Wang, Jingfen Wang, Lu Gan, Daren Lin, Zhong Ouyang, Ting Xu, Yilan Liu, Yuan Lv. Two and a half years follow-up data of HER2-targeted bispecific antibody KN026 combined with docetaxel as first-line treatment for HER2-positive recurrent/metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-29-02.