HER2-targeting Antibody-drug Conjugate Research Articles

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

Objectives: 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. Methods: 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. Results: 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). Conclusions: 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.

First-in-human study of DP303c, a HER2-targeted antibody-drug conjugate in patients with HER2 positive solid tumors

DP303c is a HER2-targeted ADC with a cleavable linker-MMAE payload. Previous in vitro studies demonstrated that DP303c showed similar or better antitumor activity than T-DM1 in xenograft models. This was a multicenter, dose escalation and dose expansion phase 1 study in China. Eligible patients were 18-75 years old with HER2-positive advanced solid tumors who were unable to benefit from standard therapy. DP303c was administered intravenously every 3 weeks, with accelerated titration at lower dose of 0.5 mg/kg and 3 + 3 design with dose levels of 1.0, 2.0, 3.0 or 4.0 mg/kg at dose escalation part, followed by the selected dose level at dose expansion part. The primary endpoints were safety and tolerability, as well as identification of recommended phase 2 dose. As of Feb 28, 2023, 94 patients were enrolled and received DP303c (dose escalation: n = 22; dose expansion: n = 72), of whom 68 patients had breast cancer. One dose limiting toxicity (Grade 3 eye pain) was observed at 4.0 mg/kg dose, and the maximum tolerated dose was not reached. The most common treatment-related adverse events at grade 3 or higher were blurred vison (16.0%), dry eye (6.4%), and peripheral neuropathy (5.3%). No treatment-related death occurred. Overall, among 91 efficacy evaluable patients, 39 patients (42.9%) achieved an objective response. Disease control was observed in 62 patients (68.1%). In 66 efficacy evaluable patients with breast cancer, 34 patients achieved an objective response (51.5%). Disease control was achieved in 51 patients (77.3%). Median PFS was 6.4 months. On a molar basis, DP303c Cmax at 3.0 mg/kg doses was 132-folder higher than that for free MMAE. DP303c demonstrated promising anti-tumor activity with acceptable safety in patients with pre-treated advanced HER2 positive solid tumors, especially in breast cancer. Based on safety and efficacy results, 3.0 mg/kg Q3W was determined as recommended phase 2 dose for DP303c. (Trial registration: ClinicalTrials.gov Identifier: NCT04146610).

759P JSKN003, a HER2-targeting antibody-drug conjugate, in patients with platinum-resistant ovarian cancer: A pooled analysis of two studies

759P JSKN003, a HER2-targeting antibody-drug conjugate, in patients with platinum-resistant ovarian cancer: A pooled analysis of two studies

Therapeutic indications for antibody-drug conjugates estimated from HER2 and p53 expressions in endometrial carcinoma

ObjectiveWhile human epidermal growth factor receptor 2 (HER2) is upregulated in endometrial carcinoma—especially in the p53 aberrant type— conventional anti-HER2 therapy is not typically used for this cancer type. Recently, HER2-targeted antibody-drug conjugates have shown antitumor effects against HER2 low-expressing cancers. Therefore, we analyzed the clinicopathological characteristics of HER2-positive endometrial carcinomas including those with low expression, as well as the prognostic significance of p53 and HER2 co-expression. MethodsImmunohistochemistry for HER2 and p53 was performed in 530 patients with endometrial carcinoma; 124 cases (23%) were HER2-positive. ResultsOf the HER2-positive cases, >50% were 1+. A high prevalence of HER2 expression was observed in serous (64%), clear-cell (73%), and mixed (64%) carcinomas. Notably, 19% of endometrioid carcinomas were HER2-positive. HER2 positivity was significantly associated with age ≥60 years, high-grade histological subtype, deep myometrium invasion, stage III/IV, recurrence, and death. Univariate analysis showed that HER2-positive cases had reduced progression-free survival (PFS) (p = 0.007) and overall survival (OS) (p = 0.012). However, after adjusting for stage, HER2 positivity was not associated with survival. In the early stage, co-expression of HER2-positive and p53 aberrant types was associated with shorter PFS (p < 0.001) and OS (p < 0.001) compared with at least one negative result. Multivariate analysis of PFS showed HER2 and p53 co-expression (hazard ratio, 1.891; 95% confidence interval, 1.183–5.971, p = 0.008) as an independent prognostic factor. ConclusionsThis study presents detailed clinicopathological characteristics and the prognostic impact of HER2-positivity in endometrial carcinomas. HER2-targeted antibody-drug conjugate therapy may be broadly applicable to endometrial carcinoma.

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.

A DXd/TLR7-agonist dual-conjugate anti-HER2 ADC exerts robust anti-tumor 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 MTT-5, 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 (TME). This is achieved by promoting immune cell infiltration and activating dendritic cells and CD8+T cells via MTT-5. In vivo evaluation of Tras-DXd-MTL1's anti-tumor potency revealed a notably superior performance compared to 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.

The Evolving Paradigm of Antibody-Drug Conjugates Targeting the ErbB/HER Family of Receptor Tyrosine Kinases.

Current therapies targeting the human epidermal growth factor receptor (HER) family, including monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs), are limited by drug resistance and systemic toxicities. Antibody-drug conjugates (ADCs) are one of the most rapidly expanding classes of anti-cancer therapeutics with 13 presently approved by the FDA. Importantly, ADCs represent a promising therapeutic option with the potential to overcome traditional HER-targeted therapy resistance by delivering highly potent cytotoxins specifically to HER-overexpressing cancer cells and exerting both mAb- and payload-mediated antitumor efficacy. The clinical utility of HER-targeted ADCs is exemplified by the immense success of HER2-targeted ADCs including trastuzumab emtansine and trastuzumab deruxtecan. Still, strategies to improve upon existing HER2-targeted ADCs as well as the development of ADCs against other HER family members, particularly EGFR and HER3, are of great interest. To date, no HER4-targeting ADCs have been reported. In this review, we extensively detail clinical-stage EGFR-, HER2-, and HER3-targeting monospecific ADCs as well as novel clinical and pre-clinical bispecific ADCs (bsADCs) directed against this receptor family. We close by discussing nascent trends in the development of HER-targeting ADCs, including novel ADC payloads and HER ligand-targeted ADCs.

A high hydrophobic moment arginine-rich peptide screened by a machine learning algorithm enhanced ADC antitumor activity.

Cell-penetrating peptides (CPPs) with better biomolecule delivery properties will expand their clinical applications. Using the MLCPP2.0 machine algorithm, we screened multiple candidate sequences with potential cellular uptake ability from the nuclear localization signal/nuclear export signal database and verified them through cell-penetrating fluorescent tracing experiments. A peptide (NCR) derived from the Rev protein of the caprine arthritis-encephalitis virus exhibited efficient cell-penetrating activity, delivering over four times more EGFP than the classical CPP TAT, allowing it to accumulate in lysosomes. Structural and property analysis revealed that a high hydrophobic moment and an appropriate hydrophobic region contribute to the high delivery activity of NCR. Trastuzumab emtansine (T-DM1), a HER2-targeted antibody-drug conjugate, could improve its anti-tumor activity by enhancing targeted delivery efficiency and increasing lysosomal drug delivery. This study designed a new NCR vector to non-covalently bind T-DM1 by fusing domain Z, which can specifically bind to the Fc region of immunoglobulin G and effectively deliver T-DM1 to lysosomes. MTT results showed that the domain Z-NCR vector significantly enhanced the cytotoxicity of T-DM1 against HER2-positive tumor cells while maintaining drug specificity. Our results make a useful attempt to explore the potential application of CPP as a lysosome-targeted delivery tool.

Preclinical studies of BB-1701, a HER2-targeting eribulin-containing ADC with potent bystander effect and ICD activity.

Several HER2-targeting antibody-drug conjugates (ADC) have gained market approval for the treatment of HER2-expressing metastasis. Promising responses have been reported with the new generation of ADCs in patients who do not respond well to other HER2-targeting therapeutics. However, these ADCs still face challenges of resistance and/or severe adverse effects associated with their particular payload toxins. Eribulin, a therapeutic agent for the treatment of metastatic breast cancer and liposarcoma, is a new choice of ADC payload with a distinct mechanism of action and safety profile. We've generated a novel HER2-tageting eribulin-containing ADC, BB-1701. The potency of BB-1701 was tested in vitro and in vivo against cancer cells where HER2-expressing levels vary in a large range. Bystander killing effect and toxin-induced immunogenic cell death (ICD) of BB-1701 were also tested. In comparison with HER2-targeting ADCs with DM1 and Dxd payload, eribulin-containing ADC demonstrated higher in vitro cytotoxicity in HER2-low cancer cell lines. BB-1701 also effectively suppressed tumors in models resistant to DM1 or Dxd containing ADCs. Mode of action studies showed that BB-1701 had a significant bystander effect on HER2-null cells adjacent to HER2-high cells. In addition, BB-1701 treatment induced ICD. Repeated doses of BB-1701 in nonhuman primates showed favorable pharmacokinetics and safety profiles at the intended clinical dosage, route of administration, and schedule. The preclinical data support the test of BB-1701 in patients with various HER2-expressing cancers, including those resistant to other HER2-targeting ADCs. A phase I clinical trial of BB-1701 (NCT04257110) in patients is currently underway.

Trastuzumab deruxtecan (DS-8201a), a HER2-targeting antibody-drug conjugate, demonstrates in vitro and in vivo antitumor activity against primary and metastatic ovarian tumors overexpressing HER2.

High-grade serous ovarian cancer (HGSOC) and ovarian clear cell carcinoma (CC), are biologically aggressive tumors endowed with the ability to rapidly metastasize to the abdominal cavity and distant organs. About 10% of HGSOC and 30% of CC demonstrate HER2 IHC 3 + receptor over-expression. We evaluated the efficacy of trastuzumab deruxtecan (T-DXd; DS-8201a), a novel HER2-targeting antibody-drug conjugate (ADC) to an ADC isotype control (CTL ADC) against multiple HGSOC and CC tumor models. Eleven ovarian cancer cell lines including a matched primary and metastatic cell line established from the same patient, were evaluated for HER2 expression by immunohistochemistry and flow cytometry, and gene amplification by fluorescence in situ hybridization assays. In vitro experiments demonstrated T-DXd to be significantly more effective against HER2 3 + HGSOC and CC cell lines when compared to CTL ADC (p < 0.0001). T-DXd induced efficient bystander killing of HER2 non-expressing tumor cells when admixed with HER2 3 + cells. In vivo activity of T-DXd was studied in HER2 IHC 3 + HGSOC and CC mouse xenograft models. We found T-DXd to be significantly more effective than CTL ADC against HER2 3 + HGSOC (KR(CH)31) and CC (OVA10) xenografts with a significant difference in tumor growth starting at day 8 (p = 0.0003 for KR(CH)31, p < 0.0001 for OVA10). T-DXd also conferred a survival advantage in both xenograft models. T-DXd may represent an effective ADC against primary and metastatic HER2-overexpressing HGSOC and CC.

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.

3D layered co-culture model enhances Trastuzumab Deruxtecan sensitivity and reveals the combined effect with G007-LK in HER2-positive non-small cell lung cancer

Human epidermal growth factor receptor 2 (HER2) aberrations are observed in various cancers. In non-small cell lung cancer, genetic alterations activating HER2, mostly exon 20 insertion mutations, occur in approximately 2–4% of cases. Trastuzumab deruxtecan (T-DXd), a HER2-targeted antibody-drug conjugate has been approved as the first HER2-targeted drug for HER2-mutant lung cancer. However, some cases are not responsive to T-DXd and the primary resistant mechanism remains unclear. In this study, we assessed sensitivity to T-DXd in JFCR-007, a patient-derived HER2-mutant lung cancer cell line. Although JFCR-007 was sensitive to HER2 tyrosine kinase inhibitors, it showed resistance to T-DXd in attachment or spheroid conditions. Accordingly, we established a three-dimensional (3D) layered co-culture model of JFCR-007, where it exhibited a lumen-like structure and became sensitive to T-DXd. In addition, an in-house inhibitor library screening revealed that G007-LK, a tankyrase inhibitor, was effective when combined with T-DXd. G007-LK increased the cytotoxicity of topoisomerase-I inhibitor, DXd, a payload of T-DXd and SN-38. This combined effect was also observed in H2170, an HER2-amplified lung cancer cell line. These results suggest that the proposed 3D co-culture system may help in evaluating the efficacy of T-DXd and may recapitulate the tumor microenvironment.

Human epidermal growth factor receptor 2 (HER2) status in breast cancer: practice points and challenges.

Human epidermal growth factor receptor 2 (HER2)-enriched breast cancer benefits significantly from anti-HER2 targeted therapies. This highlights the critical need for precise HER2 immunohistochemistry (IHC) interpretation serving as a triage tool for selecting patients for anti-HER2 regimens. Recently, the emerging eligibility of patients with HER2-low breast cancers for a novel HER2-targeted antibody-drug conjugate (T-DXd) adds challenges to HER2 IHC scoring interpretation, notably in the 0-1+ range, which shows high interobserver and interlaboratory staining platform variability. In this review, we navigate evolving challenges and suggest practical recommendations for HER2 IHC interpretation.

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.

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.

Identification of HER2 ultra-low based on an artificial intelligence (AI)-powered HER2 subcellular quantification from HER2 immunohistochemistry images.

1115 Background: HER2-targeted antibody-drug conjugates (ADCs) can effectively target tumor cells even in HER2-low breast cancers (1+ and 2+/no amp). We developed an AI-based whole-slide image (WSI) analyzer for immunohistochemistry (IHC)-stained slides, exploring a cutoff differentiating between true HER2 negative versus HER2 ultra-low. Methods: An AI-based IHC WSI analyzer was developed using 6,188 WSIs stained by 19 types of IHC including HER2 and from various cancers, annotated by 153 pathologists. The model predicts cells as tumor cells or non-tumor cells and generates HER2 expression continuous score (HER2ecs, 0-100%), quantifying IHC staining intensity of membrane, nucleus, cytoplasm, and membrane+cytoplasm separately for each cell. A total of 401 HER2 IHC WSIs were acquired from Samsung Medical Center (n=275), Kyung Hee University Hospital (n=78), and Commercial Biobank (n=48), scored as 0 (n=347) and 1+ (n=54) by pathologists. Results: In total, 67,169,114 tumor cells and 119,113,886 non-tumor cells from 401 WSIs were successfully evaluated. Comparing HER2 score 0 versus 1+ by pathologists, mean HER2ecs of nucleus (1.7% vs 4.1%), cytoplasm (6.5% vs 12.9%), and membrane (3.6% vs 8.2%) were comparable. In HER2 score 0 WSIs, membrane HER2ecs of tumor cell was 3.6 ± 7.8% (mean ± standard deviation), while that of non-tumor cell was 0.9 ± 2.9% (p &lt;0.001 vs. tumor cell), suggesting, even in HER2 score 0 cases, tumor cell exhibits HER2 expression beyond non-specific HER2 staining intensity. Based on our internal validation dataset, membrane-specific HER2ecs of 6.0% was the optimal threshold discriminating HER2 no-staining cells versus HER2 incomplete and faint/barely perceptible cells (AI-HER2-weak) per ASCO/CAP guideline. Among HER2 score 0 by pathologists, when applying this cutoff, the proportion of WSIs showing AI-HER2-weak or higher membrane-specific HER2ecs in over 10% of all tumor cells was 23.6% (82/347). Interestingly, that of WSIs among HER2 score 1+ by pathologists was 51.9% (28/54), which is comparable to 52.3%, objective response rate of trastuzumab deruxtecan in HER2-low patients in DESTINY-Breast04. Conclusions: AI-powered subcellular-level analysis enables identification of 23.6% HER2 ultra-low WSIs among HER2 score 0 by pathologist, which is defined by AI-HER2-weak or higher membrane-specific HER2 expression ≥ 10%. Clinical validation of the AI-powered HER2 ultra-low definition is warranted.

Efficacy and safety of disitamab vedotin (RC48) in HER2-expressing breast cancer: A multicenter retrospective study.

e13011 Background: RC48 is an Antibody-Drug Conjugate (ADC) that integrates a humanized monoclonal antibody targeting human epidermal growth factor receptor 2 (HER2) linked to the microtubule inhibitor monomethyl auristatin E (MMAE). This study reports real-world data using RC48 monotherapy in HER2-expressing advanced breast cancer (ABC). Methods: The study reviewed patients with HER2-expressing ABC who received RC48 monotherapy at three hospitals in China between September 2021 and June 2022. The electronic medical record was used to collect the clinical characteristics of the patient and to evaluate the antitumor activity and safety. The primary outcome was real-world progression-free survival (rwPFS). Results: A total of 15 patients were included, of whom 9(60%) were HER2-positive and 6(40%) had HER2 low expression (IHC 1+ or IHC 2+/ISH-).11 patients (73.3%) had visceral metastases, 40% of patients (6/15) had central nervous system (CNS) metastases at baseline. 6 patients (40%) had ≥3 metastatic lesions, and 13(86.7%) of patients received RC48 as third-line treatment or higher. Progression-free survival (PFS), overall survival (OS), and response can be assessed in all patients. The median follow-up was 10 months and the median rwPFS was 8.0 months (95% CI, 4.897-11.103), while the median OS was not reached. Objective response rate (ORR) and disease control rate (DCR) were 46.7% and 80% respectively. Partial response (PR) was achieved in 46.7% of the patients (7/15). patients with HER2-positive and HER2 low expression, the median rwPFS was 8.77 and 4.63 months, respectively (HR = 0.49,95% Cl, 0.13-1.80, P = 0.196), and in 6 patients with CNS metastases, the median rwPFS was 7.5 months (95% CI, 2.82-18.28). The most common treatment-related adverse events (TRAEs) were elevated transaminase (33.3%) and Leukopenia (33.3%), most of which were grade 1-2, No serious adverse events related to treatment were observed. Conclusions: The novel HER2-targeted ADC, RC48, demonstrated promising preliminary antitumor activity in patients with HER2-expressing ABC, patient with brain metastases could also benefit, with tolerable toxicities.

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.

A single-arm, multicenter, phase 2 clinical study of recombinant humanized anti-HER2 monoclonal antibody-MMAE conjugate (MRG002) in HER2-positive unresectable locally advanced or metastatic urothelial carcinoma

BackgroundMRG002 is a novel HER2-targeted antibody-drug conjugate being investigated in the MRG002–006 trial to evaluate the efficacy and safety in HER2-positive urothelial carcinoma patients. MethodsThis is an open-label, single-arm, multicenter phase II study. Eligibility criteria included: histologically confirmed HER2 IHC 2 + or 3 + UC, prior received ≥ 1 standard treatment. Patients in this study received MRG002 every 3 weeks until progressive disease or unacceptable toxicity. The primary endpoint was confirmed ORR per RECIST 1.1. ResultsAs of February 24, 2023, a total of 43 patients were enrolled. The median age was 60. 9 patients were dosed at 2.6 mg/kg and 34 patients were dosed at 2.2 mg/kg. At baseline, most patients (29/43) received ≥ 2 lines of treatment and 35 (81.4%) patients had prior ICI therapy. FISH test was performed in 41 patients and 9 (22.0%) were positive. By the cut-off date, 41 patients were evaluable and the ORR was 53% (95%CI：38.9%−67.5%), with 6.9% CR, and the DCR was 83.7% (95%CI：70.0%−91.9%). The median PFS and OS for the 43 patients were 7.0 months (95%CI：5.4-NE) and 14.9 months (95%CI：11.9-NE), respectively. The ORR was 77.8% in 9 patients with positive HER2 FISH results. Most common treatment-related AEs were anemia (51.2%), alopecia (44.2%) and neutropenia (39.5%); most were grade 1 or 2. ConclusionPreliminary results of MRG002 demonstrated a clinically meaningful response in pretreated HER-2 positive unresectable locally advanced or metastatic UC patients. MRG002 at 2.2 mg/kg was well tolerated with a manageable toxicity.

Abstract PS11-06: Analysis of HER2 expression changes from breast primary to brain metastases including HER2 Low and impact on overall survival

Abstract Background: Previous studies have shown that breast cancer receptor subtype switching between matched primary and metastatic brain metastases (BrM) is common. HER2 expression at low levels, termed “HER2 Low”, has emerged as a new therapeutic biomarker for highly active antibody drug conjugates with potential intracranial activity. Trastuzumab deruxtecan is FDA approved for the treatment of HER2 Low and HER2 positive breast cancer with emerging evidence of CNS responses and clinical benefit in patients with BrM. This study aimed to investigate the relationship between HER2 expression including HER2-Low between matched breast cancer primary tumors and brain metastases. We also sought to evaluate the impact of low HER2 expression on overall survival in breast cancer brain metastases. Methods: We identified pts with MBC seen at least once at a single, NCI-designated center and had a diagnosis of BrM between 2003 and 2023. Of 1252 MBC pts with a diagnosis of BrM, 265 pts underwent resection/biopsy for BrM with available ER/PR/HER2 status. Only pts with available matched primary and BrM tissue were analyzed. HER2 expression was defined as: HER2+ (3+ or 2+/ISH amplified), HER2-Low (1+, 2+/ISH neg) or HER2-0 [by ASCO-CAP guidelines]. Estrogen receptor (ER) status was defined as ER≥1%. Multivariate overall survival (OS) analyses by Cox proportional hazard models were determined from time of BrM resection to death or last follow-up between HER2+, HER2-Low and HER2-0 patients controlling for ER and age. Results: 197 matched breast cancer primary and BrMs with available ER, PR, and HER2 testing were evaluated. Median age at BrM resection was 51 yrs. ER was positive in 48% (N=95) of BrMs. Of 265 resected BrMs, HER2 expression was found in 72%: 49.8% HER2+ (N=132), 22.2% HER2-Low (N=59), and 27.9% HER2-0 (N=74). HER2 expression by 197 primary tumors was: 57% HER2+ (N=112), 24% HER2-Low (N=48), 19% HER2 0 (N=37). Amongst 112 HER2+ primary tumors, 97% (N=109) had concordant HER2+ BrMs, 3 (2.6%) switched to HER2-Low, with 100% retaining some HER2 expression. Of 37 HER2-0 primaries, 35% (13/37) gained HER2-Low expression and 5.4% (2/37) gained HER2+ expression in the BrM. Amongst 48 HER2-Low primary tumors, half (52%) changed expression to either HER2+ (21%) or HER2-0 (31.2%) in the brain. 66 tumors had extracranial tissue biopsied prior to BrM resection available for HER2 analysis. Of 15 HER2-0 extracranial tumors, 47% gained HER2-Low and 13% gained HER2+ at time of BrMs. After adjusting for age and ER status at the time of BrMs, patients with HER2+ BrM had a statistically significant lower risk of death at time of follow up than those with HER2-Low BrM (HR=0.41, P=0.0006). The risk of death between patients with HER2-0 BrM did not differ from HER2-Low BrM after adjustment for ER and age (HR=0.96, p =0.9). Median survival from BrM resection was 12.4m, 16.1m, 47.6m for HER2-Low, HER2-0 and HER2+ respectively (p = .0004). Conclusions: HER2 expression amongst primary, extracranial and brain metastases is dynamic with frequent change. Over 40% of HER2-0 primary or extracranial tumors gain HER2 expression in the brain. These changes have therapeutic implications given HER2 targeting antibody drug conjugates with improved OS and emerging evidence of CNS activity, highlighting the need for better diagnostics, including those that do not require invasive tissue sampling, to determine HER2 status in the brain. Patients with HER2-Low and HER2-0 BrMs have inferior survival and are a clinical unmet need. Citation Format: Alyssa Pereslete, Melissa Hughes, Alyssa Patterson, Janet Files, Kyleen Nguyen, Lauren Buckley, Ashka Patel, Abigail Moore, Eric Winer, Tianyu Li, Sara Tolaney, Nancy Lin, Sarah Sammons. Analysis of HER2 expression changes from breast primary to brain metastases including HER2 Low and impact on overall survival [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 PS11-06.