Antibody-drug Conjugate Therapy Research Articles

Fully Automated Artificial Intelligence Solution for Human Epidermal Growth Factor Receptor 2 Immunohistochemistry Scoring in Breast Cancer: A Multireader Study.

The proven efficacy of human epidermal growth factor receptor 2 (HER2) antibody-drug conjugate therapy for treating HER2-low breast cancers necessitates more accurate and reproducible HER2 immunohistochemistry (IHC) scoring. We aimed to validate performance and utility of a fully automated artificial intelligence (AI) solution for interpreting HER2 IHC in breast carcinoma. A two-arm multireader study of 120 HER2 IHC whole-slide images from four sites assessed HER2 scoring by four surgical pathologists without and with the aid of an AI HER2 solution. Both arms were compared with high-confidence ground truth (GT) established by agreement of at least four of five breast pathology subspecialists according to ASCO/College of American Pathologists (CAP) 2018/2023 guidelines. The mean interobserver agreement among GT pathologists across all HER2 scores was 72.4% (N = 120). The AI solution demonstrated high accuracy for HER2 scoring, with 92.1% agreement on slides with high confidence GT (n = 92). The use of the AI tool led to improved performance by readers, interobserver agreement increased from 75.0% for digital manual read to 83.7% for AI-assisted review, and scoring accuracy improved from 85.3% to 88.0%. For the distinction of HER2 0 from 1+ cases (n = 58), pathologists supported by AI showed significantly higher interobserver agreement (69.8% without AI v 87.4% with AI) and accuracy (81.9% without AI v 88.8% with AI). This study demonstrated utility of a fully automated AI solution to aid in scoring HER2 IHC accurately according to ASCO/CAP 2018/2023 guidelines. Pathologists supported by AI showed improvements in HER2 IHC scoring consistency and accuracy, especially for distinguishing HER2 0 from 1+ cases. This AI solution could be used by pathologists as a decision support tool for enhancing reproducibility and consistency of HER2 scoring and particularly for identifying HER2-low breast cancers.

Detection of SEZ6, a therapeutic target, in medullary thyroid carcinoma.

Seizure-related 6 homolog (SEZ6) is a cDNA that strongly associated with neuroendocrine differentiation. Recently, SEZ6 expression was found in a subset of small cell lung carcinoma (SCLC). Furthermore, ABBV-011, a novel antibody drug conjugate targeting SEZ6 has been developed and is currently in clinical trial in treating SCLC and neuroendocrine neoplasms, including medullary thyroid carcinoma (MTC). We herein presented the first evidence that SEZ6 was highly expressed in MTC. SEZ6 immunoexpression was studied in 78 MTCs and correlated with clinicopathologic characteristics, outcome, and molecular profile. SEZ6 was highly expressed in primary tumors, regional recurrence, and distant metastasis. Using two different SEZ6 antibody clones SC17.14 and 14E5, SEZ6 immunopositivity was seen in 91% to 93% of primary MTCs, 100% of regional recurrence, and 75% to 83% of distant metastasis. High level of SEZ6 immunoexpression determined using H score was associated with male sex, advance stage, and extrathyroidal thyroidal extension. There was no correlation between SEZ6 expression and outcome or RET/RAS mutation status in MTC. The frequency of SEZ6 positivity in MTC without RET/RAS mutations were 83%. SEZ6 may serve as a novel biomarker for MTCs. Although SEZ6 lacks any prognostic values in MTC, its positivity in 91% to 93% of MTCs, including MTCs without RET and RAS mutations, renders SEZ6-targetted antibody-drug conjugate therapy a promising targeted therapy for MTCs.

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.

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.

Imaging and Monitoring HER2 Expression in Tumors during HER2 Antibody-Drug Conjugate Therapy Utilizing a Radiolabeled Site-Specific Single-Domain Antibody Probe: 68Ga-NODAGA-SNA004-GSC.

The overexpression of HER2 is pivotal in the initiation and progression of breast cancer. Developing HER2-targeted radiotracers is crucial for noninvasive assessment of HER2 expression, patient selection for HER2-targeted therapy, monitoring treatment response, and identifying resistance. Here, we reported a nonsite-specific coupled radiotracer, 68Ga-NOTA-SNA004-His6, and a site-specific coupled radiotracer, 68Ga-NODAGA-SNA004-GSC, based on a novel HER2 nanobody, SNA004. Both radiotracers exhibited high affinity, specific targeting, and rapid clearance in vitro and in vivo. Additionally, these tracers and trastuzumab showed noncompetitive binding to HER2. Compared to 68Ga-NOTA-SNA004-His6, 68Ga-NODAGA-SNA004-GSC demonstrated significantly reduced renal and liver uptake. PET/CT imaging with 68Ga-NODAGA-SNA004-GSC sensitively detected the responsiveness of various tumor models to trastuzumab and its antibody-drug conjugates (ADCs). Overall, the site-specific coupled radiotracer 68Ga-NODAGA-SNA004-GSC offered significant advantages in biodistribution and signal-to-noise ratio, making it a valuable tool for monitoring HER2 expression levels before, during, and after trastuzumab and ADC treatment.

Antibody-Drug Conjugates in Urothelial Cancer: From Scientific Rationale to Clinical Development.

Antibody-drug conjugates (ADCs) have been a significant advancement in cancer therapy, particularly for urothelial cancer (UC). These innovative treatments, originally developed for hematological malignancies, use target-specific monoclonal antibodies linked to potent cytotoxic agents. This rational drug design efficiently delivers cancer cell-killing agents to cells expressing specific surface proteins, which are abundant in UC owing to their high antigen expression. UC is an ideal candidate for ADC therapy, as it enhances on-target efficacy while mitigating systemic toxicity. In recent years, considerable progress has been made in understanding the biology and mechanisms of tumor progression in UC. However, despite the introduction of immune checkpoint inhibitors, advanced UC is characterized by rapid progression and poor survival rates. Targeted therapies that have been developed include the anti-nectin 4 ADC enfortumab vedotin and the fibroblast growth factor receptor inhibitor erdafitinib. Enfortumab vedotin has shown efficacy in prospective studies in patients with advanced UC, alone and in combination with pembrolizumab. The anti-Trop-2 ADC sacituzumab govitecan has also demonstrated effectiveness in single-armed studies. This review highlights the mechanism of action of ADCs, their application in mono- and combination therapies, primary mechanisms of resistance, and future perspectives for their clinical use in UC treatment. ADCs have proven to be an increasingly vital component of the therapeutic landscape for urothelial carcinoma, filling a gap in the treatment of this progressive disease.

Abstract PO-006: ABBV-319: A CD19–targeting glucocorticoid receptor modulator antibody-drug conjugate therapy for B-cell malignancies

Abstract Glucocorticoids such as prednisone (P) and dexamethasone (D) are key components in standard-of-care immuno-chemotherapy regimens (e.g., R-CHOP, EPOCH-R, Hyper-CVAD) for the treatment of B-cell malignancy. However, prolonged systemic glucocorticoid treatment is associated with several adverse events that often result in dose reduction and reduced therapeutic efficacy. ABBV-319 is a CD19-targeting antibody-drug conjugate (ADC) with a glucocorticoid receptor modulator (GRM) payload engineered to reduce glucocorticoid-associated toxicities while possessing three distinct mechanisms of action (MOA) to increase therapeutic efficacy: (1) CD19 receptor-mediated delivery of potent glucocorticoid receptor modulator (GRM) payload to induce apoptosis, (2) inhibition of B-cell receptor (BCR) stimulated CD19 signaling, and (3) enhanced Fc-mediated effector function via afucosylation of the antibody backbone. ABBV-319 elicited potent GRM-driven anti-tumor activity against multiple malignant B-cell lines in vitro as well as in cell line-derived xenografts (CDXs) and patient-derived xenografts (PDXs) in vivo. Remarkably, a single-dose of ABBV-319 induced sustained tumor regression and enhanced anti-tumor activity compared to repeat dosing of systemic prednisolone at the maximum tolerated dose (MTD) in mice. The unconjugated CD19 monoclonal antibody (mAb) also displayed anti-proliferative activity on a subset of B-cell lymphoma cell lines through the inhibition of PI3K signaling. Moreover, afucosylation of the CD19 mAb enhanced Fc-mediated antibody-dependent cellular cytotoxicity (ADCC), and this activity was maintained after conjugation with GRM payload. Notably, ABBV-319 displayed superior efficacy compared to afucosylated CD19 mAb in human CD34+ PBMC-engrafted NSG-tg(Hu-IL15) transgenic mice, demonstrating enhanced anti-tumor activity in vivo when multiple MOAs are enabled concurrently. ABBV-319 also showed potent anti-tumor activity across multiple B-cell lymphoma models, including non-germinal center B-cell (GCB) DLBCL and relapsed lymphoma treated with R-CHOP treatment. Collectively, these data support the ongoing evaluation of ABBV-319 for the treatment of B-cell malignancy in Phase I clinical trial (NCT05512390). Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication. Citation Format: Chewei (Anderson) Chang. ABBV-319: A CD19–targeting glucocorticoid receptor modulator antibody-drug conjugate therapy for B-cell malignancies [abstract]. In: Proceedings of the Fourth AACR International Meeting on Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2024 Jun 19-22; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(3_Suppl):Abstract nr PO-006.

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.

Identifying mutations in ctDNA to predict antibody-drug conjugate response in breast cancer.

e13074 Background: Metastatic breast cancer (mBC) is a complex disease, and outcomes remain poor because new therapies are needed. A new class of drugs, antibody-drug conjugate (ADC), has shown effectiveness across all breast cancer subtypes. Yet FDA- approval for these therapies is restricted only to HER2 and triple-negative subtypes. Therefore, we urgently need to identify which patients, regardless of subtype, will respond to ADCs. The advent of circulating tumor DNA (ctDNA) offers a unique noninvasive method to capture breast cancer (BC) heterogeneity. Recently, ctDNA testing has been employed in clinical practice to guide targeted therapies for mBC, particularly in cases of hormone receptor positive (HR+) disease with mutations in PIK3CA and ESR1. The clinical implications to predict response to ADC therapy in BC remains unclear. Here we test the hypothesis that ctDNA can detect mutations that predict response to novel ADCs. Methods: We analyzed a subset of patients from the Dallas Metastatic Breast Cancer Study comprised of patients with mBC who underwent ctDNA testing using the Tempus xF liquid biopsy ctDNA sequencing panel. The data was analyzed from a single academic medical center between the initial year of ctDNA collection in 2019 to 2023. We identified detectable mutations from patients and addressed a relationship by using Metascape. Relevant signaling pathways were identified: APOBEC, ErbB signaling, p53 and Ras-MAPK pathway. Patients with triple negative, HER2, and HR BC were examined for ADC response and associated mutations. Survival analyses were estimated using Kaplan-Meier and Gehan Breslow Wilcoxon test for statistical analysis. Results: We identified 43 patients with HR+ mBC who had at least one mutation within the Ras-MAPK pathway and 10 of 43 received ADC therapy. Median survival of patients who received ADC therapy 58 months (n=10) vs not receiving ADC therapy 33 months (n=33) (p &lt; 0.05). Of the ten patients who received ADC treatment, 60% had 1+ HER2 staining on tissue biopsy. 70% of patients received Trastuzumab deruxtecan (T-DXd) and 30% received Sacituzumab govitecan (SG). SG was given to patients with negative HER2 staining on biopsy. Patients with at least one mutation within ABOBEC, ErbB signaling, and p53 pathways did not have statistically significant differences in mOS. Conclusions: In HR+ mBC, detection of mutated genes associated with the Ras-MAPK pathway by ctDNA was associated with a more favorable response when treated with ADCs. These findings are exciting because HR+ BCs are being targeted with ADCs regardless of HER2 or TROP2 expression, highlighting the need for new biomarkers to distinguish which HR+ patients to treat. Our retrospective analysis findings are limited by the number of patients with ctDNA testing and also timing of testing. Further studies are needed to solidify the observed correlation between Ras-MAPK pathway mutations and favorable response to ADC treatment.

Assessment of carcinoembryonic antigen-related cell adhesion molecule 5 expression by immunohistochemistry in real-world clinical samples of non-small cell lung cancer.

e20013 Background: Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) is an emerging target of antibody-drug conjugate therapy for non-small cell lung cancer (NSCLC). High expression of CEACAM5 has been reported in approximately 25% of patients with lung adenocarcinoma (Lefebvre AM, et al. Lung Cancer. 2023; 184:107356). However, CEACAM5 expression has not been systematically examined in a real-world patient population with NSCLC. In this study, we evaluated our experience in the assessment of CEACAM5 expression by immunohistochemistry (IHC) in routinely diagnosed clinical samples. Methods: We assessed the expression of CEACAM5 by IHC on clinical biopsy/resection samples of consecutively diagnosed NSCLC from September 2022 to June 2023 at our institution, using the anti-CEACAM5 clone 769 antibody assay protocol developed for tusamitamab ravtansine clinical trials. Only cases adequate for PD-L1 22C3 and Oncomine Comprehensive Assay v3 NGS assay were included. CEACAM5 expression was scored independently by three pathologists based on the method proposed by Lefebvre et al. Expression levels were categorized as high (≥ 50% tumor cells at ≥ 2+ intensity), moderate (1–49% tumor cells at ≥ 2+ intensity), and negative (0 or 1+ intensity). Interrater reliability was assessed by Kendall’s coefficient of concordance (KCC) and Fleiss’ Kappa. Discordant classification was reviewed with the final classification achieved by consensus. Association with PD-L1 TPS and NGS results was determined by Chi-squared test. Results: This study cohort consisted of 150 consecutively diagnosed NSCLC, including 133 adenocarcinomas and 17 squamous cell carcinomas. The samples were derived from both primary (n = 138) and metastatic sites (n = 12). Both membranous and cytoplasmic CEACAM5 expression was observed in neoplastic cells, but was consistently absent in nonneoplastic cells. The prevalence of consensus high CEACAM5 membranous expression was 21% (n = 32) overall, 20% in primary (n = 28) and 33% (n = 4) in metastatic sites. The level of interrater agreement across all categories was moderate (KCC = 0.77). Interrater agreement between high CEACAM5 expression versus moderate/negative categories combined was also moderate (Kappa = 0.60). Challenging features included the determination of staining intensity and mixed membranous and cytoplasmic staining pattern, and cases near the cut-offs of the defined categories. CEACAM5 expression was not associated with PD-L1 TPS (p = 0.42) or EGFR mutations (p = 0.44). Conclusions: Our data showed that approximately 20% of routinely diagnosed clinical NSCLC samples had high CEACAM5 expression by IHC. The interrater reliability on the determination of high CEACAM5 expression was moderate among the three pathologists. We highlighted the challenging aspects in the evaluation of this biomarker.

SV-BR-1-GM after progression on ADC in patients with metastatic breast cancer.

1087 Background: Antibody-drug conjugate (ADC) sequencing raises concerns of cross-resistance due to their shared targets and cytotoxic payloads. Consequently, treatments after ADCs in heavily pretreated MBC is uncertain. SV-BR-1-GM, a GM-CSF secreting, antigen-presenting immortalized breast cancer cell line, has emerged as a post ADC solution (1) based on a different MOA. We now report the results of SV-BR-1-GM in ADC treated patients. Methods: Post-hoc analysis of an ongoing randomized Phase 2 censored to the data-cut date prior to data lock. Bria-IMT (~20x106 SV-BR-1-GM cells, intradermally 48-72 hours after ctx (300 mg/m2), followed by interferon-alpha 2 days later) administered q3wks with a checkpoint inhibitor (CPI). Adverse events were classified according to their severity and relationship to treatment regimen. Results: Among 54 advanced MBC patients randomized, 23 who failed prior ADC therapy were identified. All were heavily pretreated (median 6 prior lines, range 3 – 13). Median age 62 (41-83). 14 pts had HR+/HER2-, 5 TNBC, and 2 HR+/HER2+ MBC. The remaining were HR-/HER2+ or HR-/HER2 low. 8 pts received &gt; 1 ADC. Prior ADCs included: 4 ado-trastuzumab emtansine, 14 trastuzumab deruxtecan, 13 sacituzumab govitecan. 7 pts had also received ≥ 1 prior CPI line. To date, pts received a median 3 cycles of Bria-IMT™ + CPI (2-8). Kaplan-Meier analysis revealed a median OS of 42 weeks with survival of 69% at 6 months. The subset experienced a median PFS of 74 days with 40% of pts demonstrating a Bria-IMT PFS (PFS2) similar to or &gt; their prior line PFS (PFS1). 39% of pts experienced a PFS2 ≥ their most recent line of ADC PFS. The disease control rate was 40% among evaluable pts. 43% of pts had a reduction in cancer-associated macrophage-like cell (CAML) levels; median reduction was 36% (22-98%) after 1 cycle. There were no toxicity-related treatment discontinuations. 43% (10/23) reported grade 3 or 4 AEs, independent of study drug causality. AEs included injection site reaction (39%), fatigue (26%), and nausea/vomiting (43%), mostly mild to moderate. One case of elevated lipase was the most clinically significant grade 4 AE. No interstitial lung disease (ILD) was reported. Conclusions: This subset analysis of the Bria-IMT regimen in ADC refractory MBC patients suggests a potential clinical benefit and treatment option for this patient population. The absence of serious AEs, notably interstitial lung disease (ILD), and no toxicity-related treatment discontinuations, underscores the regimen's favorable safety profile. Future studies are warranted to confirm these results and explore the potential of Bria-IMT™ in broad clinical settings of heavily pretreated contemporary MBC patients. 1. Kamaraju 2024 AACR. Clinical trial information: NCT03328026 .

Evaluation of the safety, pharmacokinetics, and efficacy of JSKN003 in patients with advanced solid tumors: A phase I/II clinical study.

3031 Background: JSKN003 is a bispecific HER2-directed antibody-drug conjugate (ADC) conjugated to a topoisomerase I inhibitor via a dibenzocyclooctyne tetrapeptide linker on the glycan of a humanized bispecific antibody. Pre-clinical studies showed that JSKN003 had a good serum stability, that may lead to a broader therapeutic window. Methods: JSKN003-102 (NCT05744427) is a phase I (dose escalation and dose expansion) and phase II (cohort expansion) study in Chinese patients (pts) with advanced solid tumors. Pts (ECOG PS 0-1) with HER2-expressing (IHC ≥ 1+) or HER2-mutant cancers who failed prior systemic therapies were recruited and received JSKN003 monotherapy intravenously Q3W. The objectives were safety, MTD or RP2D, pharmacokinetics, and preliminary antitumor activity. Here the results from phase I were reported. Results: As of 5th Jan 2024, 46 pts (25 breast cancers, 11 gastric cancers, 8 colorectal cancers, 1 lung cancer, and 1 ovarian cancer) were enrolled and received JSKN003 across 6 dose levels, including 2.1 (n=1), 4.2 (n=10), 5.2 (n=14), 6.3 (n=15), 7.3 (n=3), and 8.4 mg/kg (n=3), Q3W, in phase I period. Among the 46 pts, 18 were IHC 3+, 21 were IHC 2+, and 7 were IHC 1+. Most pts (73.9%) received ≥ 3 prior lines of therapy, including 60.9% and 45.6% of pts received prior anti-HER2 and anti-HER2 ADC therapy, respectively. The median duration of treatment was 13.1 (range, 2.1 - 42.4) weeks, and 37 pts (80.4%) remained on treatment. Treatment-related adverse events (TRAEs) occurred in 44 pts (95.7%), and the common, mostly grade 1 and 2, were diarrhea (37.0%) and nausea (32.6%). Only 6 pts (13.0%) experienced grade ≥3 TRAEs, and the common were lymphopenia (4.3%) and neutropenia(4.3%). 1 pt (2.2%) had treatment related SAE (nausea, grade 3). No pts experienced DLT or interstitial lung disease, and no TRAE led to death or discontinuation. Following a single dose, exposures (Cmax and AUC) of JSKN003 increased proportionally over a dose range of 4.2 mg/kg to 6.3mg/kg. T1/2 of JSKN003 is approximately 3-5 days. No significant accumulation was observed after 4 cycles treatment. The exposure of released payload was very low, demonstrating the stability of the JSKN003 in circulation. 37 pts had at least one post-baseline tumor assessment. The ORR and DCR was 51.4% (95%CI: 34.4, 68.1) and 91.9% (95%CI: 78.1, 98.3), respectively. The ORR in pts with HER2 IHC 1+, 2+ and 3+ was 20.0% (95% CI: 0.5, 71.6), 33.3% (95% CI: 11.8, 61.6), and 76.5% (95% CI: 50.1, 93.2), respectively. For pts who received prior anti-HER2 ADC, the ORR was 57.9% (95% CI: 33.5, 79.7). For HER2 positive breast cancer and gastric cancer, the ORR was 66.7% (95% CI: 38.4, 88.2) in 15 pts and 100% (95% CI: 39.8, 100) in 4 pts, respectively. Conclusions: MTD of JSKN003 was not reached yet. And safety of JSKN003 was extremely excellent with encouraging preliminary antitumor activity in heavily pretreated pts with advanced solid tumors. Clinical trial information: NCT05744427 .

Abstract B014: FGFR inhibition upregulates Nectin-4 expression in FGFR3 altered urothelial carcinoma

Abstract Bladder urothelial carcinoma (UC) is a common malignancy and remains a significant cause of mortality; however, in recent years there have been substantial advances in the treatment of metastatic UC (mUC). This includes the approval of the antibody drug conjugate (ADC) enfortumab vedotin, which targets Nectin-4, and the fibroblast growth factor receptor (FGFR) inhibitor erdafitinib (in FGFR2/3 altered tumors). Despite the impressive efficacy of these agents, most patients will ultimately develop progressive disease, underlining the need for further therapeutic development. Previous work has demonstrated that NECTIN4 expression and FGFR3 alterations are enriched in luminal subtypes of UC and NECTIN4 expression is higher in FGFR altered tumors. We validate these findings in scRNAseq from primary tumors as well as bulk RNAseq from murine models. Given the positive correlation between NECTIN4 and FGFR3 alterations we hypothesized that FGFR3 inhibition would downregulate Nectin-4 expression. To our surprise we found in vitro treatment with erdafitinib in cell lines with FGFR3 fusion proteins (RT112, RT4, SW780) lead to an increase in Nectin-4 protein levels. Additionally, in vitro FGFR inhibition in the UMUC-14 cell line which harbors an FGFR3S249C hotspot mutation, upregulates Nectin-4 protein levels. To further investigate this phenomenon, we engineered the FGFR3 WT cell line, 5637 to overexpress FGFR3-TACC3 or FGFR3S249C. We saw that FGFR3-TACC3 and FGFR3S249C overexpression both down regulated Nectin-4 indicating that FGFR3 activity negatively regulates Nectin-4 expression. We have also investigated the association between FGFR inhibition and Nectin-4 expression in two in vivo models: (1) in a xenograft model using the RT112 line we found an overall increase in Nectin-4 expression in tumors treated with a 5-day course of erdafitinib; (2) in a UPFL1 (a cell line derived from a genetically engineered mouse with a S249C mutation) syngeneic model we also saw an increase in Nectin-4 expression after erdafitinib treatment. We have observed that the increase in Nectin-4 expression persists in vitro even after withdrawal of erdafitinib treatment, indicating that intermittent dosing of erdafitinib maybe be sufficient to prime a tumor for Nectin-4 targeted therapy. Lastly, preliminary in vitro investigation of the combination of erdafitinib and enfortumab vedotin in RT112 cells showed synergy, particularly with lower doses of both agents, providing further support of our hypothesis that FGFR3 inhibition may act to sensitize UC to Nectin-4 ADC therapy. A potential synergistic relationship is further supported by the recent results of the phase 1 trial investigating the combination of erdafitinib plus enfortumab vedotin in which the objective response rate was 100% (9/9 patients: 8 PRs &amp; 1CR). Citation Format: Sean Clark-Garvey, Mi Zhou, Michael Sturdivant, Wolfgang Beckabir, Lucia Kim, E. Drew Toomer, Ian McCabe, Akihiro Hamada, Daniel Crona, Jeffrey S. Damrauer, William Y. Kim. FGFR inhibition upregulates Nectin-4 expression in FGFR3 altered urothelial carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B014.

Assessment of HER2 status in extramammary Paget disease and its implication for disitamab vedotin, a novel humanized anti-HER2 antibody-drug conjugate therapy.

Assessment of HER2 status in extramammary Paget disease and its implication for disitamab vedotin, a novel humanized anti-HER2 antibody-drug conjugate therapy.

Cardiovascular adverse events associated with antibody-drug conjugates (ADCs): a pharmacovigilance study based on the FAERS database.

As a novel drug formulation, antibody drug conjugates (ADCs) are widely used in various types of cancer. However, clinically, there is a lack of attention to the CVD produced by them, as well as a lack of research on the real-world situation. Using the Food and Drug Administration Adverse Event Reporting System (FAERS) database, to ensure its clinical safety application, we analyzed post-marketing data on antitumor ADCs to identify risk factors and drugs associated with the risk of cardiovascular events. We used OpenVigil 2.1 to conduct a database query for adverse events (AEs) reported to the FAERS database between the time the drug was launched and the second quarter of 2023. Cardiovascular adverse events (AEs) were grouped into fourteen narrow categories using the Standardized Medical Dictionary for Regulatory Activities (MedDRA) Queries (SMQs), and the reporting odds ratio (ROR) and the proportional reporting ratio (PRR) for reporting the association between different drugs and cardiovascular disease (CVD) risk were calculated. In the FAERS database, 1863 AEs associated with CVD we studied were identified in patients receiving ADC therapy. Most reports came from people aged ≥65, but a significant number of cases were found to be unknown. The number of patients with antibody-drug conjugates (ADCs)-related CVD cases aged <18years, 18-64years, and≥ 65years was 52 (2.79%), 586 (31.45%), and 613 (32.90%), respectively. The proportion of female patients (834, 44.77%) was higher than that of male patients (752, 40.37%). Death (770 reports), disability (9 reports), Hospitalization initial or prolonged (407 reports), and life-threatening reactions (187 reports). Of the 770 deaths reported, 103 (31.7%) were associated with brentuximab vedotin, 10 (24.4%) with sacituzumab govitecan, 22 (19.3%) with enfortumab vedotin, and 35 (34.7%) with trastuzumab emtansine.49 (41.2%) cases were associated with polatuzumab vedotin, 62 (29%) with trastuzumab deruxtecan, 423 (54.3%) with gemtuzumab ozogamicin, and 66 (38.8%) with inotuzumab ozogamicin. In a disproportionate number of SMQS, cardiac failure (n = 277) and embolic and thrombotic events, venous (n = 446) were the most frequently reported CVD-related AEs in ADCs. By mining the FAERS database, we provided relevant information on the association between ADC use and cardiovascular-associated AEs. ADCs were associated with increased cardiovascular toxicity, deserving distinct monitoring and appropriate management. Further research is needed to confirm these findings and assess causality.

Abstract PO3-13-11: Quantitative Multiplex Immunofluorescence Assay for TROP2 and HER2 Expression in Breast Cancer: Towards Guiding Patient Selection for Antibody Drug Conjugate Therapies

Abstract Emerging antibody drug conjugate (ADC) therapies targeting human trophoblast cell-surface antigen (TROP2) and human epidermal growth factor receptor 2 (HER2) are transforming the treatment landscape for breast cancer. Sacituzumab govitecan (SG) and trastuzumab deruxtecan (T-DXd) have gained approval for an overlapping set of "HER2-low" metastatic breast cancers, including hormone receptor (HR)-positive HER2 non-amplified and "triple-negative" subtypes. Nevertheless, the optimal selection of patients and treatment sequencing for these ADC therapies remains a clinical challenge. Clinical trial objective response rates to SG are approximately 30%, compared to 30-90% for T-DXd depending on HER2 expression levels. While both drugs are thought to be targeted therapies, the value of measuring the target and the best methods to do so are still not established. We believe that quantitative measurement of TROP2 and HER2 antigen expression levels could establish thresholds for responders, enabling more effective patient selection for ADC therapies. Here, we present a TROP2, high-sensitivity HER2, and cytokeratin (CK) quantitative immunofluorescence (QIF) multiplex assay. Using a ten-cell line standard array and proteomic mass spectrometry, we can convert tumor compartment QIF intensity to protein concentration in fmol/mm2 for tissue specimens. Anti-HER2, anti-TROP2 antibodies, and fluorescence detection systems were titrated and combined to maximize signal-to-noise ratio on our cell line standard array and breast cancer tissue microarrays (TMA). The multiplex assay was designed for automated slide stainers (Leica BOND Rx) and fluorescence slide scanning (Rarecyte CyteFinder II HT). We perform our analyses in QuPath using an image processing plugin developed for automated QIF/IHC analysis (Qymia). Reproducible TROP2 and HER2 QIF scoring (R² &amp;gt; 0.95) was achieved across multiple staining batches using serial sections of breast cancer TMAs and cell standard arrays. This assay has a TROP2 linear range between 0.63 - 9.17 fmol/mm2 (about 1 million TROP2 receptors/cell) and HER2 linear range between 0.09 - 0.565 fmol/mm2 (about 60,000 HER2 receptors/cell). We then applied this multiplex assay to two serial retrospective primary breast cancer cohorts from Yale University to quantitatively measure TROP2 and HER2 expression (338 clinical cases). We find a weak negative correlation between TROP2 and HER2 expression in our breast cancer cohorts (Pearson r = -0.14, p = 0.0097, n = 338). TROP2 expression levels were above the limit of detection (LOD) in 90.2% of cases, with 4.1% exceeding the limit of linearity (LOL), and a mean TROP2 expression of 4.05 fmol/mm2. For HER2, 67.2% of cases were above the LOD, with 7.1% exceeding the LOL, and a mean HER2 expression of 0.186 fmol/mm2. Both TROP2 and HER2 were below the LOD in 3.0% of cases, which we define as “negative”. We found 29.9% expressed TROP2 and were HER2-negative, and 6.8% expressed HER2 and were TROP2-negative. Our future studies will aim to quantitatively define expression thresholds for T-DXd and SG response with the goal to produce a clinical grade assay for ADC patient selection and determine the value of the assay to help select which ADC to give first. HER2 and TROP2 protein expression summary in Yale breast cancer cohort Table 1: Summary of HER2 and TROP2 protein expression levels in serial retrospective primary breast cancer cohort of 338 cases using our high-sensitivity HER2 and TROP2 multiplex immunofluorescent assay Citation Format: Charles Robbins, Mengni He, Revekka Khaimova, Katherine Bates, Nay Nwe Nyein Chan, Daniel Liebler, Regan Fulton, David Rimm. Quantitative Multiplex Immunofluorescence Assay for TROP2 and HER2 Expression in Breast Cancer: Towards Guiding Patient Selection for Antibody Drug Conjugate Therapies [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 PO3-13-11.

Abstract PO5-17-09: Event-free survival in HER2-low vs HER2-zero breast cancer patients submitted to neoadjuvant chemotherapy

Abstract Background: Breast cancer (BC) with low expression of HER2 (HER2-low) might constitute a group of tumors with unique clinical and biological characteristics. However, the prognostic impact of HER2-low status vs HER2-zero in terms of pathological complete response (pCR) and event-free survival (EFS) after neoadjuvant chemotherapy (NACT) remains controversial. The aim of this study was to evaluate pCR and EFS rates in HER2-low vs HER2-zero early BC patients treated with NACT. Methods: In this cross-sectional study, we analyzed 565 consecutive patients with HER2-low and HER2-zero early BC submitted to neoadjuvant therapy from 2017 to 2021 in a single academic center. Patients with biopsy-confirmed stage I-III BC, with HER2-low or HER2-zero status, submitted to locoregional therapy after NACT were included. Clinical and pathological characteristics, pathological response, treatment protocol and RFS were analyzed and considered for statistical analysis. HER2-low was defined by IHC 1+, or 2+ ISH non-amplified; HER2-zero was defined by IHC 0. Pathological response was determined locally, and pCR defined as the absence of residual invasive disease with or without ductal carcinoma in situ in the breast and axilla. EFS was defined as the time from diagnosis to distant recurrence, a second primary, or death from any cause, whichever occurred first. Results: 441 patients were included in the analysis, 236 (53.5%) patients with HER2-low tumors, and 205 (46.5%) with HER2-zero tumors. Overall, 279 (63.3%) were estrogen receptor (ER)-positive tumors, and 162 (36.5%) were ER-negative tumors. Among ER-positive tumors, 166 (59.5%) had HER2-low status, and 113 (40.5%) were HER2-zero. For the ER-negative subgroup, the corresponding rates were 70 (43.2%) and 92 (56.8%), respectively. Most patients had stage II-III BC (423/441; 96%), and 20.2% (89/441) had high nodal tumor burden. Many patients received anthracycline- and taxane-based NACT (425/441; 96.4%), and over 90% (148/162; 91.3%) of ER-negative patients received a platinum agent. The overall pCR rate were 18.1%. Among ER+ tumors, pCR rates were 6.4%, 6.0%, and 7.0% in the overall, HER2-low and HER2-zero tumors, respectively. In ER- tumors, the corresponding pCR rates were 38.3%, 35.7, and 40.2%, respectively. The differences in pCR rates between HER2-low and HER2-zero tumors were not statistically significant (ER-positive, p=0.724; ER-negative, p=0.559). After a median follow-up of 42 months, 90 EFS events occurred. In the HER2-low group there were 56 (23.7%) EFS events, and 34 (16.6%) EFS events in the HER2-zero (HR 1.19; 95% CI 0.77-1.82; p=0.427). Among 279 patients in the ER-positive group there were 48 events, 32 in the HER2-low subgroup and 16 in the HER2-zero group (HR 1.16; 95% CI 0.64-2.13; p=0.622). Among 162 ER-negative tumors there were 42 events, 24 in the HER2-low subgroup, and 24 in the HER2-zero subgroup (HR 1.56; 95% CI 0.84-2.88; p=0.158). NACT discontinuation occurred in 86 patients (ER-positive: 45, 16.1%; ER-negative: 41, 25.3%), mainly due to toxicity (anthracycline-taxane: 10.0%; platinum: 11.7%). Disease progression during NACT were reported in 6.8% (30/441) of patients. Conclusions: Our results show similar pCR rates and RFS among HER2-low and HER2-zero early BC patients after standard NACT, which are consistent with the current literature. Despite the predictive role of low HER2 expression in selecting patients for novel antibody-drug conjugates (ADCs) therapy, its prognostic value could not be confirmed. Citation Format: Guilherme Sartori, Susana Ramalho, Leonardo Roberto da Silva, Tomás Reinert, Mahira Lopes Da Rosa, Grazielle Morais Tavares, Vivian Vasconcelos, Higor Mantovani, Ana Elisa Ribeiro Da Silva Cabello, Guilherme Coelho, Jovana Mandelli, Facundo Zaffaroni, César Cabello, Carlos Barrios, Marcia Silveira Graudenz. Event-free survival in HER2-low vs HER2-zero breast cancer patients submitted to neoadjuvant chemotherapy [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 PO5-17-09.

Abstract PO4-12-06: Interstitial Lung Disease (ILD) in Sequential Antibody Drug Conjugate (ADC) use in patients with Metastatic Breast Cancer (MBC): A Multi-Institutional experience

Abstract Introduction: Interstitial Lung Disease (ILD) is a known adverse event associated with Antibody Drug Conjugates (ADCs), causing fibrosis of the lung. In the DESTINY-Breast 04, TROPICS-02, and ASCENT trials the rate of ILD/Pneumonitis was 12.1%, 0.4%, and 0% respectively. In these studies, the time to first cross-sectional imaging after initiation of ADC was 6 weeks. However, prior treatment with a topoisomerase-1 inhibitor ADC was not permitted in these studies, so the influence of sequential ADC treatments remains unknown. Here, we aimed to characterize the frequency and management of ILD in sequential use of ADCs in a multi-institution retrospective analysis. Methods: We identified patients (pts) with HR+/HER2-low and HR-/HER2-low MBC who had received both Trastuzumab-deruxtecan (T-DXd) and Sacituzumab govitecan (SG) monotherapy (in either order, with or without intervening therapies) who were treated at five academic centers between 2020-2023. Patients had received treatment with the ADC in either routine clinical treatment or as a prior participant on a clinical trial with ADC monotherapy. Information regarding ILD diagnosis, imaging, timing of onset, peak and resolution along with management information was collected and analyzed. Retrospective assessment of ILD toxicity was graded using CTCAE v5.0, based on available clinical and radiographic reports. Results: 10/60 pts who received ADC therapy in this multi-institutional cohort were diagnosed with ILD (all grades). No differences in age or BMI were observed in those who developed ILD versus those who did not, and 9/10 pts were White, 1 was Asian, with a median age of 59 years (47-79 years). Pertinent history in these pts included 3/10 had a prior smoking history, 8/10 had a prior cardiac or pulmonary comorbidity (including sleep apnea, lung cancer, hypertension, hyperlipidemia, thrombosis, or stroke). Prior to receiving their first ADC, 7/10 patients had metastatic disease to the lung. All 10 patients were diagnosed with ILD during treatment with T-DXd. 4 pts initially received T-DXd, then developed ILD and then upon recovery, subsequently received SG. The remaining 6 pts initially received SG (with no reports of ILD), and then received T-DXd and subsequently developed ILD. In the entire cohort, the median time from ADC initiation to first CT scan was 8 weeks (range 1-22 weeks). Within the cohort that developed ILD, the median time from initiation of T-DXd to first CT scan was also 8 weeks (range 6-13 weeks). The median time to diagnoses of ILD was 3 months after initiation of T-DXd (range 0.4-14.5 months). Dyspnea was the most common presenting symptom in 9/10 pts and at diagnosis of ILD, dyspnea was graded as III in 6/10 pts, II in 3/10 pts, and I in 1/10 pts. Diagnostic evaluation included CT chest (9/10), pulmonary consultation (8/10), pulmonary function testing (2/10), and bronchoscopy (1/10). 4/10 patients presented at their highest-grade toxicity at diagnosis. All patients stopped T-DXd treatment, 7 were hospitalized, 7 required supplemental oxygen, and 8 were prescribed steroids for treatment. Of those receiving steroids, the most common starting dose was prednisone 1 mg/kg and doses ranged from 0.5 mg/kg to 9mg/kg prednisone equivalents. No patient received a secondary immunosuppressive agent. The steroid treatment duration ranged from 1-4 months. None of the 10 pts underwent re-challenge with T-DXd and 3/10 developed grade V ILD (death). Conclusion: We observed a 16.6% incidence of all grade ILD (5% grade V ILD) with T-DXd and 0% with SG. In this small cohort study, we did not observe a clear increased risk for ILD with sequential treatment of ADCs. Practice patterns were consistent with recommended diagnostic evaluation and steroid management. Additional strategies are needed to characterize pts most at risk for developing ILD and to identify situations where re-challenge may be safe. Citation Format: Sarah Premji, Laura Huppert, Reshma Mahtani, Samantha Fisch, Naomi Dempsey, Angelina Raimonde-Taylor, Saya Jacob, Laura Quintal, Jo Chien, Michelle Melisko, Ana Sandoval-Leon, Lauren Carcas, Manmeet Ahluwalia, Natasha Harpalani, Jenna Hoppenworth, Dame Idossa, Ruta Rao, Hope Rugo, Karthik Giridhar. Interstitial Lung Disease (ILD) in Sequential Antibody Drug Conjugate (ADC) use in patients with Metastatic Breast Cancer (MBC): A Multi-Institutional experience [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 PO4-12-06.

Abstract PO3-15-12: Expression and co-expression patterns of TROP2 and HER2 in breast cancer: implications for bispecific antibody-drug conjugate therapy

Abstract Introduction: Antibody-drug conjugates (ADCs) targeting trophoblast cell surface antigen 2 (TROP2), such as sacituzumab-govitecan and datopotamab-deruxtecan, have recently been developed. A preclinical study has reported the efficacy of anti-human epidermal growth factor receptor 2 (HER2) and TROP2 bispecific ADCs in treating HER2 and TROP2 co-expressing tumors, including HER2-low tumors in various solid tumors (Chengzhang Shang et al: AACR 2023). In this study, we aimed to evaluate the expression of TROP2 by immunohistochemistry (IHC) at different sites and investigate the changing status and co-expression of HER2 and TROP2 among breast cancer patients. Methods: We collected 244 archival paired samples of primary tumors and metastatic sites from 111 breast cancer patients treated in our hospital from 2000 to 2018. Estrogen receptor (ER), progesterone receptor (PgR), and HER2 status were determined from previous pathology reports. HER2 low was defined as HER2 IHC score of 1+ or 2+ with negative fluorescent in situ hybridization (ISH). In addition, we determined the expression of TROP2 using IHC assays and categorized the results based on the histochemical score (H-score). Results: Among the samples, ER+HER2- was 139, ER+HER2+ was nine, ER-HER2+ was eight, and triple-negative (TN) was 88. HER2 3+ or 2+ with ISH positive was 17, HER2 low was 112, HER2 negative was 115. The median TROP2 H-score was 10, with a mean of 37.5 (range: 0-265). Overall, 27% of the samples had H-score of 0, 73% had H-score of 1&amp;lt;, 47% had H-score of 10&amp;lt;, and 12% had H-score of 100&amp;lt; . No statistically significant association was observed between TROP2 expression and breast cancer subtypes (ER+HER2-; H-score of 0 24%, H-score of 1&amp;lt; 76%, H-score of 10&amp;lt; 44%, H-score of 100&amp;lt; 14%, TN; H-score of 0 30%, H-score of 1&amp;lt; 70%, H-score of 10&amp;lt; 54%, H-score of 100&amp;lt; 11%). On the other hand, samples from the metastatic site showed a higher rate of TROP-2 expression H-score of 1&amp;lt; compared to the primary site (primary site; H-score of 0 36%, H-score of 1&amp;lt; 64%, metastatic site; H-score of 0 18%, H-score of 1&amp;lt; 82%; p&amp;lt; 0.01). The rates of TROP2-positive expression defined as H-score of 1&amp;lt;, varied among the metastatic sites, with 100% in liver, 92% in brain, 89% in lymph nodes, 64% in lung, and 60% in bone. Regarding the co-expression of HER2 and TROP2, among HER2-positive samples, 35% had TROP2 H-score of 0, 24% had TROP2 H-score of 1&amp;lt;, and 41% had TROP2 H-score of 10&amp;lt;, while among HER2 low samples, 21% had TROP2 H-score of 0, 27% had TROP2 H-score of 1&amp;lt;, 39% had TROP2 H-score of 10&amp;lt;, and TROP2 H-score of 100&amp;lt; was found in 13% of patients. Based on the definition of co-expression such as TROP2 H-score of 1&amp;lt; and HER2 1+ or more, overall, 40% of the samples had co-expression of HER2 and TROP2, and the metastatic site had a higher rate of co-expression than the primary tumor (49%, 32% respectively, p=0.002). Conclusions: This study demonstrates that TROP-2 expression by IHC in breast cancer varies between primary and metastatic sites in breast cancer. Metastatic sites and specific organs show higher rate of TROP2 expression. Additionally, 40% of the samples had the co-expression of HER2 and TROP2, suggesting a potential target for future bispecific ADCs therapy. Citation Format: Mai Onishi, Tatsunori Shimoi, Yuki Kojima, Shu Yazaki, Taro Yamanaka, Rui Kitadai, Asuka Kawachi, Hitomi Okuma, Mai Hoshino, Ayumi Saito, Munehiro Ito, Aiko Maejima, Tadaaki Nishikawa, Kazuki Sudo, Emi Noguchi, Yasuhiro Fujiwara, Masayuki Yoshida, Kan Yonemori. Expression and co-expression patterns of TROP2 and HER2 in breast cancer: implications for bispecific antibody-drug conjugate therapy [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 PO3-15-12.

Abstract GS02-01: Randomized phase 3 study of datopotamab deruxtecan vs chemotherapy for patients with previously-treated inoperable or metastatic hormone receptor-positive, HER2-negative breast cancer: Results from TROPION-Breast01

Abstract Background: The global, phase 3 TROPION-Breast01 trial (NCT05104866) assessed the TROP2-directed antibody-drug conjugate (ADC) datopotamab deruxtecan (Dato-DXd) compared with investigator’s choice of chemotherapy (ICC) in patients (pts) with inoperable or metastatic hormone receptor-positive, HER2-negative (HR+/HER2‒) breast cancer (BC). Primary results were presented at ESMO 2023 (Bardia A, et al. Abstract LBA11). Here we report expanded data from TROPION-Breast01. Methods: Pts aged ≥18 years who had inoperable or metastatic HR+/HER2‒ BC, had disease progression on endocrine therapy (ET) and for whom ET was unsuitable, and had received 1‒2 prior lines of systemic chemotherapy (CT), were eligible. Pts were randomized 1:1 to Dato-DXd (6 mg/kg Q3W) or ICC (eribulin, vinorelbine, capecitabine, or gemcitabine) until progression or unacceptable toxicity. The dual primary endpoints were progression-free survival (PFS) by blinded independent central review (BICR) per RECIST 1.1, and overall survival (OS). Results: In total, 732 pts were randomized: 365 to the Dato-DXd arm and 367 to ICC. At data cut-off (Jul 17, 2023), 93/39 pts in the Dato-DXd/ICC groups were ongoing treatment. Pts receiving Dato-DXd had significantly improved PFS vs ICC (HR 0.63 [95% CI 0.52‒0.76]; p&amp;lt;0.0001). Hazard ratios for PFS favored Dato-DXd over ICC across prespecified pt subgroups, including prior lines of CT in the metastatic setting (1 vs 2), prior use of CDK4/6 inhibitor (≤12 months vs &amp;gt;12 months), prior use of endocrine therapy in the metastatic setting ( &amp;lt;6 months vs ≥6 months) and brain metastases (yes vs no). OS data were not mature at this data cut-off. In the Dato-DXd vs ICC arms, 192 (53%) vs 247 (67%) pts had received a subsequent therapy after study treatment discontinuation, including 15 (4%) vs 52 (14%) who received subsequent ADC therapy, and 165 (45%) vs 186 (51%) who received subsequent CT. Median time to first subsequent therapy was 8.2 months in the Dato-DXd arm vs 5.0 months in the ICC arm (HR 0.53 [95% CI 0.45–0.64). Overall, rate of grade ≥3 treatment-related adverse events (TRAEs) with Dato-DXd was less than half that with ICC. The secondary patient-reported outcome endpoints showed that time to deterioration in physical functioning, pain, and global health status/quality of life were delayed in the Dato-DXd arm compared with ICC. Conclusions: TROPION-Breast01 met its dual primary endpoint of PFS, demonstrating statistically significant and clinically meaningful improvement in PFS with Dato-DXd compared with ICC across all subgroups. Overall, the safety profile and QoL with Dato-DXd was favorable compared with ICC. These data support Dato-DXd as a potential new therapeutic option for pts with inoperable or metastatic HR+/HER2‒ BC who have received 1‒2 prior lines of CT. Citation Format: Aditya Bardia, Komal Jhaveri, Seock-Ah Im, Michelino De Laurentiis, Binghe Xu, Sonia Pernas, Giuliano Borges, David Cescon, Masaya Hattori, Yen-Shen Lu, Noelia Martínez-Jáñez, Erika Hamilton, Shusen Wang, Junji Tsurutani, Kevin Kalinsky, Lu Xu, Sabrina Khan, Neelima Denduluri, Hope Rugo, Barbara Pistilli. Randomized phase 3 study of datopotamab deruxtecan vs chemotherapy for patients with previously-treated inoperable or metastatic hormone receptor-positive, HER2-negative breast cancer: Results from TROPION-Breast01 [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 GS02-01.