Validation and Prospective Testing of a High Sensitivity, Quantitative Analytic Assay for HER2 on Histopathology Slides.

Antibody-drug conjugates are effective in the treatment of HER2-amplified breast cancer and Hodgkin's lymphoma, but current ADC technologies have faced limitations expanding the addressable patient population and target space. Ado-trastuzumab emtansine (T-DM1) is an ADC with 3-4 cytotoxic drugs per antibody that was recently approved for HER2 IHC 3+ or HER2-amplified breast cancer. Even within this high HER2-expressing population, several studies have now shown greater T-DM1 benefit in patients with HER2 mRNA expression above the median. These data suggest the need for more potent anti-HER2 ADCs to maximize benefit for HER2 IHC 3+ or amplified patients, and to extend HER2 ADC therapy to low HER2-expressing patients (HER2 IHC 1+/2+). XMT-1522 is an anti-HER2 ADC that uses a novel, human anti-HER2 antibody optimized for cytotoxic payload delivery, and is non-competitive with trastuzumab or pertuzumab for HER2 binding. Each antibody is conjugated to ∼15 proprietary auristatin molecules using Fleximer, a biodegradable hydrophilic polymer. XMT-1522 shows nanomolar potency in cultured tumor cells with HER2 receptor densities as low as 10,000 per cell, and is typically 1-3 logs more potent than T-DM1 across a panel of 25 tumor cell lines. In mouse xenograft studies XMT-1522 has excellent pharmacokinetic properties and achieves complete tumor regressions at well-tolerated doses. In the high HER2-expressing N87 gastric cancer model (800,000 HER2 receptors/cell), complete regressions are achieved with a single 1 mg/kg dose of XMT-1522, while 10 mg/kg T-DM1 is required for comparable activity. In the same model, the XMT-1522/trastuzumab/pertuzumab triple combination results in tumor regressions where the same doses of XMT-1522 alone or the trastuzumab/pertuzumab doublet result in tumor stasis. In the low HER2-expressing JIMT-1 breast cancer (79,000 HER2/cell) and SNU5 gastric cancer (22,000 HER2/cell) models, complete regressions are achieved with single 1 mg/kg or 0.67 mg/kg doses of XMT-1522, respectively, while T-DM1 is inactive at doses ≥10 mg/kg. In non-human primates XMT-1522 demonstrates good stability of drug conjugate in plasma with t1/2 ∼5 days (comparable to antibody t1/2) and minimal exposure to free payload. Despite the high potency of XMT-1522 in low HER2 tumor models, there is no XMT-1522-related toxicity observed in critical HER2-expressing tissues including heart and lung. The preclinical data support testing XMT-1522 as a single agent in tumors with low HER2 expression where current HER2-directed therapies are not indicated. Furthermore, combination of XMT-1522 with trastuzumab and/or pertuzumab achieves efficient cytotoxic payload delivery while retaining the potential for full inhibition of HER2 signaling, which may be necessary to improve on current regimens in HER2-driven tumors. Citation Format: Donald A. Bergstrom, Natalya Bodyak, Alex Yurkovetskiy, Peter U. Park, Michael DeVit, Mao Yin, Laura Poling, Joshua D. Thomas, Dmitry Gumerov, Dongmei Xiao, Elena Ter-Ovanesyan, LiuLiang Qin, Alex Uttard, Alex Johnson, Timothy B. Lowinger. A novel, highly potent HER2-targeted antibody-drug conjugate (ADC) for the treatment of low HER2-expressing tumors and combination with trastuzumab-based regimens in HER2-driven tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-231. doi:10.1158/1538-7445.AM2015-LB-231

Introduction Blood-based liquid biopsies are a non-invasive diagnostic approach for detecting circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) that may provide clinically actionable information for treatment decisions for metastatic breast cancer (MBC) patients when a conventional tissue biopsy is not feasible. Recently, the novel anti-HER2 antibody-drug conjugate, Trastuzumab Deruxtecan (T-DXd), has shown effectiveness against MBC with low HER2 expression detected by tissue biopsy characterized as HER2-low (immunohistochemically 1+ or 2+ and ERBB2 amplification-negative via in situ hybridization) and is being explored in an ultra-low population. Here we report on the application of a liquid biopsy platform designed to sensitively detect low levels of HER2 protein expression in CTCs from MBC patients. Methods Blood samples from 704 metastatic breast cancer patients as well as control cells lines were collected for cell-based and cell-free DNA analysis. After plasma isolation, nucleated cells deposited on glass slides went through immunofluorescent staining and imaging. CTCs were identified using Epic Sciences’ digital imaging and machine learning algorithms, and a subset of CTCs were isolated and sequenced for genomic quantification of large scale-state transitions (LSTs) as well as copy number variants (CNVs). The HER2 status was based upon on ASCO-CAP guidelines and the previous tissue biopsy results from the ordering healthcare provider, as documented on the DefineMBC™ test requisition form. Results Within a DefineMBC early-access program (EAP), 93% of patients with MBC had detectable CTCs. Among ERBB2-non-amp patients tested with the DefineMBC assay, 25% of patients with MBC had findings that were reported as consistent with HER2-low in the CAP-CLIA setting. To explore the lower boundaries of HER2 protein expression, we created and validated an MCF-7 HER2-negative ERBB2 knock-out cell line and utilized its 95% confidence level threshold (271 MFI) as a negative fluorescence cutoff for very low HER2 expression. Based upon publicly available CCLE datasets, MDA-MB-453, MCF7, and MCF7 ERBB2 KO breast cancer cell lines were selected for their high and low HER2 RNA expression levels and were corroborated via observed HER2 immunofluorescence median levels of 15740, 381, and 188 MFI respectively. In an exploratory analysis, among ERBB2-non-amp patients, we retrospectively applied the 271 MFI HER2 cutoff to the EAP cohort and identified 38% of patients with very low HER2 expression. We examined the impact of the HER2 ultra-low cutoff in patients not eligible for T-DXd treatment. Among patients reported as IHC=0 or with unknown IHC status from the most recent tissue biopsy, 44% and 42%, respectively, may qualify for treatment with T-DXd. Conclusion Using our higher sensitivity assay that combines CTC immunofluorescence and single-cell genomic analysis, we examined the lower boundary of HER2 protein expression. Feasibility data support further characterization of a very low HER2 expression phenotype, for the eventual inclusion into our comprehensive cancer profiling solution. To date, studies with biomarker expression have been limited to tissue biopsy, which may not always yield contemporaneous sampling in the metastatic setting. These results offer a liquid biopsy test that might identify patients potentially responsive to HER2-directed therapies. Citation Format: Giuseppe Di Caro, David Bourdon, Andrew Kunihiro, Alessandra Cunsolo, Ernest Lam, Megan Slade, Martin Blankfard, Lee Schwartzberg. Development of a method to detect very low levels of HER2 expression in Circulating Tumor Cells (CTCs) by liquid biopsy in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-04-04.

Antibody-drug conjugates (ADCs) are a rapidly expanding class of biopharmaceuticals for cancer targeted therapy, with fifteen ADCs approved for clinical use and over hundred candidates in clinical development. ADCs comprise a tumor-specific monoclonal antibody (mAb), to which a cytotoxic payload is attached via a linker. Approved ADCs are heterogeneous products encompassing a range of drug-to-antibody ratios (DARs), due to the chemical methods employed for conjugation. Achieving precise DAR control is expected to improve product homogeneity, pharmacokinetics (PK), safety, and clinical efficacy. In this study, we developed a rapid and efficient two-component bioconjugation system, comprising a recombinant peptidyl asparaginyl ligase (PAL) and a human glutaminyl cyclase (hQC), to conjugate anti-HER2 antibodies. Trastuzumab and disitamab were conjugated with single or branched payloads, yielding ADCs with DAR values ranging from 2 to 8. These ADCs demonstrated cytotoxicity comparable to their chemically conjugated counterparts, trastuzumab deruxtecan (DXd, Enhertu) and disitamab vedotin (Aidixi) against HER2-expressing breast cancer cell lines and PDX models. Notably, SGZ026, a PAL-conjugated trastuzumab-DXd with DAR 3.9, exhibited better in vivo mouse plasma stability compared to Enhertu (DAR 8). Despite carrying approximately half the cytotoxic payload per antibody, a single dose of SGZ026 effectively inhibited tumor growth in breast cancer PDX models with high or intermediate HER2 expression, achieving efficacy comparable to Enhertu. These findings highlight a novel and robust enzyme-based conjugation technology for developing homogenous ADCs with an improved therapeutic window.

<div>Abstract<p>SYD985 is a HER2-targeting antibody–drug conjugate (ADC) based on trastuzumab and vc-<i>seco</i>-DUBA, a cleavable linker-duocarmycin payload. To evaluate the therapeutic potential of this new ADC, mechanistic <i>in vitro</i> studies and <i>in vivo</i> patient-derived xenograft (PDX) studies were conducted to compare SYD985 head-to-head with T-DM1 (Kadcyla), another trastuzumab-based ADC. SYD985 and T-DM1 had similar binding affinities to HER2 and showed similar internalization. <i>In vitro</i> cytotoxicity assays showed similar potencies and efficacies in HER2 3+ cell lines, but in cell lines with low HER2 expression, SYD985 was 3- to 50-fold more potent than T-DM1. In contrast with T-DM1, SYD985 efficiently induced bystander killing <i>in vitro</i> in HER2-negative (HER2 0) cells mixed with HER2 3+, 2+, or 1+ cell lines. At pH conditions relevant for tumors, cathepsin-B cleavage studies showed efficient release of the active toxin by SYD985 but not by T-DM1. These <i>in vitro</i> data suggest that SYD985 might be a more potent ADC in HER2-expressing tumors <i>in vivo</i>, especially in low HER2-expressing and/or in heterogeneous tumors. In line with this, <i>in vivo</i> antitumor studies in breast cancer PDX models showed that SYD985 is very active in HER2 3+, 2+, and 1+ models, whereas T-DM1 only showed significant antitumor activity in HER2 3+ breast cancer PDX models. These properties of SYD985 may enable expansion of the target population to patients who have low HER2-expressing breast cancer, a patient population with still unmet high medical need. <i>Mol Cancer Ther; 14(3); 692–703. ©2015 AACR</i>.</p></div>

Background: Antibody drug conjugates (ADCs) against HER2 have shown meaningful clinical activity in HER2 low breast cancers, defined as 1+ or 2+ staining on immunohistochemistry (IHC) without gene amplification by in situ hybridization (ISH) techniques. Given that these methods were originally developed for an accurate detection of HER2 3+, their sensitivity and robustness for the detection of low and ultra-low levels of HER2 are questionable. We have recently described a deep learning algorithm that can detect signatures of HER2 expression based on training utilizing scanned H&E whole slide images (WSI) of breast cancers for which IHC and mRNA expression levels of HER2 were available. Here, we report the application of our algorithm to two independent breast cancer cohorts. Methods: A model was developed based on recognition of invasive breast cancer in whole slide images of H&E staining, and then trained via computational neural network with multiple instance learning for binary classification of cases as HER2 “negative” and HER2 “expressed” (low). For training, true negatives were defined as having HER2 IHC-0 and mRNA level < 7.6. HER2-low cases were defined as IHC-1+/2+ and mRNA >9. IHC-0 cases with mRNA >7.6 were excluded from the training cohorts. The resulting model (HER2Complete) was able to distinguish HER2-negatives from HER2-low cases with an AUC of 0.91 (+/- 0.08). Here we use Her2Complete to assess HER2 in two additional cohorts that include 901 ER+/HER2 IHC-0 and 52 HER2 IHC 0+ breast cancers from MSK and TCGA cohorts, respectively. For the TCGA cohort, concomitant transcriptomics data (RNASeq) as a reference for HER2 mRNA expression were retrieved and “HER2 expressed” defined as RNASeq expression of HER2 greater than the 90th percentile of the geometric mean of expression of three reference genes not expressed in breast tissues (TTN, MUC13, OR10A6). Values less than this reference cut-off in the TCGA cohort were considered “HER2 not expressed.” Results: Among the 901 IHC-0 test cases from the MSK cohort, the model identified 82 as ‘negative’, whereas 819 were found to have features of HER2 expression (HER2-Low). Of the 82 negative cases in the MSK cohort, all except 13 cases expressed mRNA levels < 9, and 786/819 of the HER2-low cases expressed mRNA levels >8. Of the 52 IHC 0+ cases in the TCGA cohort, 33 also had “HER2 not expressed” by our reference based RNASeq expression cut-off. Our model identified 15 of these 33 as ‘negative’, while 15 of the 19 TCGA cases with IHC 0+ and HER2 ‘expressed’ by our cut-off were identified as ‘HER2-Low’ by our model. Conclusions: AI tools based on the analysis of WSIs of routinely prepared H&E sections may predict HER2 status in breast cancer. This work requires further investigation using treatment response data to demonstrate that cases with morphologic features of low level HER2 expression will respond to ADCs. Citation Format: Gerard Oakley III, Jorge Reis-Filho, David Klimstra, Marc Goldfinger, Yikan Wang, Antonio Marra. Deep learning-based assessment of HER2-low expression on breast cancer H&E digital whole slide images [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-33.

Simple SummaryThe prognosis for advanced Extramammary Paget’s disease (EMPD) is almost always poor. HER2-targeted antibody–drug conjugates (ADCs) such as trastuzumab emtansine and trastuzumab deruxtecan have proven to be effective against HER2-positive breast cancers; however, no studies have addressed HER2-targeted ADCs as treatments for EMPD. We examine the efficacy of ADCs against an EMPD patient-derived xenograft (PDX) model harboring pathogenic ERBB2 mutations. Treatment with trastuzumab emtansine or trastuzumab deruxtecan was found to significantly regress EMPD-PDX tumors in only seven days, with no recurrence observed for 10 weeks. Our results suggest that HER2-targeted ADCs could be novel and promising treatment options for patients with EMPD, especially in cases with the ERBB2-mutation or ERBB2-overexpression.Extramammary Paget’s disease (EMPD) is an adenocarcinoma that develops mainly in the genital region of older adults. The prognosis for advanced EMPD is almost always poor; thus, novel therapeutic strategies need to be developed. HER2-targeted antibody–drug conjugates (ADCs) such as trastuzumab emtansine and trastuzumab deruxtecan have proven effective against HER2-positive breast cancers; however, no studies have addressed HER2-targeted ADCs as treatments for EMPD. We examine the efficacy of ADCs against an EMPD patient-derived xenograft (PDX) model harboring pathogenic ERBB2 mutations and investigate the expression levels of HER2 using EMPD clinical samples. Trastuzumab emtansine or trastuzumab deruxtecan was administered intravenously to tumor-bearing NOD/Scid mice. Treatment with trastuzumab emtansine or trastuzumab deruxtecan was found to significantly regress EMPD-PDX tumors in only seven days, with no recurrence observed for 10 weeks. EMPD tumors extracted 48 h after drug administration revealed the TUNEL-positive ratio to be significantly higher for the HER2-targeted ADC-treated tumors than for the control tumors. EMPD patients’ clinical samples revealed a significant correlation between HER2 positivity and invasion, suggesting that HER2 status is associated with tumor progression. Our results suggest that HER2-targeted ADCs could be novel and promising treatment options for patients with EMPD, especially in ERBB2-mutant or ERBB2-overexpressed cases.

<div>Abstract<p>Trastuzumab deruxtecan (T-DXd) is an ERBB2/HER2-targeting antibody–drug conjugate (ADC) with efficacy across adult cancers exhibiting variable HER2 expression. Prior studies demonstrating HER2 expression in osteosarcoma motivated a clinical trial of T-DXd in pediatric and adolescent/young adults with osteosarcoma, but the trial was terminated early because of inactivity. We evaluated the activity of T-DXd using osteosarcoma patient-derived xenograft (PDX) models and found a 22% objective response rate despite no detectable HER2 expression across PDXs tested. To further assess non-HER2–mediated activity, we evaluated the activity of T-DXd across 31 pediatric cancer cell lines and found osteosarcoma to be amongst the most resistant to T-DXd, as well as unconjugated deruxtecan, providing a potential explanation for the negative results observed in the clinical trial of T-DXd in osteosarcoma. T-DXd evaluation in PDX models representing pediatric histologies with greater intrinsic sensitivity to deruxtecan, including pediatric renal tumors and desmoplastic small round cell tumor, revealed both HER2-enhanced activity as well as substantial non-HER2–mediated activity, as evidenced by equipotent activity using an isotype-matched control ADC. Together, these results underscore translational opportunities for ADC therapeutics in tumor histologies with high sensitivity to the payload and in which enhanced tumor delivery may be mediated by antibody-targeted mechanisms as well as macromolecular characteristics of ADCs (e.g., enhanced permeability and retention effect) and tumor microenvironmental factors (e.g., proteolytic payload release). Our findings challenge the role of HER2 as a biomarker predictive of T-DXd response in pediatric cancers and support further biomarker-agnostic clinical development of T-DXd in desmoplastic small round cell tumor and pediatric renal tumors.</p></div>

569 Background: Antibody-drug conjugates such as Trastuzumab deruxtecan significantly improved progression-free and overall survival for the HER2 low expression (HER2-low) breast cancer (BC) patients, pushing the research field of HER2-low to a new climax. In fact, the traditional immunohistochemistry (IHC) to identify the HER2-low or HER2-negative expression (HER2-neg) has been challenged, and it cannot predict the prognosis of HER2-low/neg patients well. Methods: Three pathologists evaluated the HER2 expression status of the subjects via IHC. More than two pathologists judged HER2 0-2 and FISH negative samples were included in this trial. ERBB2 mRNA level of formalin-fixed, paraffin-embedded BC post-surgery specimens were detected by MammaTyper quantitative real-time polymerase chain reaction (qRT-PCR) kit. The consistency of HER2 immunohistochemistry (IHC) and MammaTyper results were analyzed by interclass correlation coefficients (ICC). Differences in disease-free survival (DFS) were assessed by Kaplan Meier analysis. Results: 793 cases were included. The ICC value between IHC and MammaTyper, assessed for HER2-neg vs HER2-low is 0.28. With a median follow up of 2.5 years, there were 36 events in the whole subjects. In the whole subjects, MammaTyper successfully showed that the prognosis of HER2-low was significantly better than HER2-neg (P < 0.001, HR = 3.497, 95%CI,1.807-6.77), but IHC could not distinguished them (P = 0.1071, HR = 1.776, 95%CI, 0.9194-3.43). Although the follow-up time is short, HER2-low subjects also showed better prognosis than HER2-neg in TNBC subjects distinguished by MammaTyper (P = 0.0271, HR = 2.912, 95%CI,1.129-7.511), not by IHC (P = 0.1032, HR = 2.213, 95%CI, 0.8512-5.756). However, in 291 cases of IHC and MammaTyper detection discordancy group, IHC results showed that the prognosis of HER2-low was worse, which was contrary to the MammaTyper results and the results of the above overall test results, suggesting that IHC could not verily reflect the amount of HER2 expression in some samples, and the prognosis of HER2-low population might be more related to the mRNA expression of HER2. Conclusions: Compared with IHC/FISH, MammaTyper qRT-PCR assay may actually reflect the prognosis of HER2-neg/low, which is expected to become a diagnostic beacon for HER2-low target drugs.

Antibody-drug conjugates (ADCs) represent a major advance in breast cancer therapy, with trastuzumab deruxtecan and sacituzumab govitecan emerging as leading agents targeting distinct tumor antigens and employing different linker-payload designs. Trastuzumab deruxtecan is a second-generation HER2-directed ADC composed of trastuzumab linked via a cleavable tetrapeptide linker to the camptothecin derivative exatecan, a highly potent topoisomerase I inhibitor. Its high drug-to-antibody ratio (DAR 8:1), membrane-permeable payload, and efficient lysosomal release confer strong antitumor activity, including a robust bystander effect in HER2-low tumors. By contrast, sacituzumab govitecan is a TROP-2-targeted ADC conjugated through a hydrolysable CL2A linker to SN-38, the active metabolite of irinotecan. Sacituzumab govitecan features a high DAR (7.6:1) and allows extracellular as well as intracellular release of SN-38, enhancing bystander killing in tumors with heterogeneous TROP-2 expression, while maintaining a favorable toxicity profile due to the lower intrinsic potency of SN-38 relative to exatecan. Since both these ADCs are conjugated to topoisomerase I inhibitors, concerns about potential cross-resistance regarding their sequencing in clinical practice are being raised, and currently there is a lack of predictive biomarkers providing a rational basis for their sequential administration. Resistance mechanisms exhibit significant heterogeneity: resistance to trastuzumab deruxtecan has been associated with mutations in TOPO I and SLX4, impaired lysosomal function, and efflux via ABC transporters. In contrast, resistance to sacituzumab govitecan is linked to overexpression of multidrug resistance proteins, particularly BCRP-mediated efflux. Clinically, trastuzumab deruxtecan has shown substantial efficacy in both HER2-positive and HER2-low breast cancer, whereas sacituzumab govitecan has demonstrated efficacy across triple-negative and hormone receptor-positive/HER2-negative breast cancers. Collectively, these agents highlight how variations in target antigen, linker chemistry, and payload potency impact ADC activity, therapeutic index, and potential strategies for sequential treatment in advanced breast cancer.Graphical

Introduction: T-DXd (trastuzumab deruxtecan) is an antibody-drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER2) composed of a humanized anti-HER2 monoclonal antibody conjugated to a DNA topoisomerase I inhibitor, DXd through a linker. Internalization of HER2-T-DXd followed by DXd release is a crucial process for T-DXd to exert its antitumor activity. T-DXd induced robust and durable responses in HER2 mutant metastatic non-small cell lung cancer (NSCLC) patients in DESTINY-Lung01 study, including those with low HER2 expression levels (Li BT, et al. NEJM 2021). One hypothesis of this T-DXd sensitivity of HER2 mutant NSCLC cells involves the potential of enhanced receptor and ADC internalization in these cells (Li BT, et al. Cancer Discov 2020). To examine this possibility further, we investigated the effect of HER2 mutations on T-DXd internalization and DXd release in transgenic cells expressing various HER2 mutants, as well as on T-DXd sensitivity in vivo. Methods: We established transgenic NCI-H322 cells expressing wild-type (WT) HER2 or various HER2 mutants and evaluated T-DXd internalization in these cells. Antitumor activity of T-DXd was examined in xenograft mouse models of transgenic NCI-H322 cells and compared between WT and each mutant. DXd concentration in tumor was also determined. In addition, in vitro internalization activity and antitumor activity of T-DXd were evaluated using NCI-H1781, the NSCLC cell line harboring an endogenous HER2 mutation (G776delinsVC). Results: Transgenic NSCLC cells expressing various HER2 mutants showed higher T-DXd internalization than WT HER2 expressing cells. There also was a negative correlation between the surface HER2 expression level and T-DXd internalization among various mutants and WT expressing cells. In xenograft models with transgenic cells, some HER2 mutant models showed higher response to T-DXd than WT HER2 model, with greater than 2-fold increase in G660D, YVMA, G776delinsVC, V777_G778insGSP, and V842I. Tumor DXd concentration was positively correlated with the antitumor activity. In an endogenous HER2 mutant NSCLC cell line (NCI-H1781), T-DXd also showed high internalization activity and potent antitumor activity. Conclusion: In vitro study with transgenic NSCLC cells suggested that T-DXd internalization in HER2 mutant tumors was more efficient than in WT HER2 tumor. Some of those HER2 mutant cell lines showed increased T-DXd sensitivity and higher payload release in the tumor in vivo, suggesting the enhanced internalization played a role in the mechanism of T-DXd sensitivity in these HER2 mutant transgenic NSCLC cells. Some mutants may be more or less clinically relevant. However, the relationship between the in vitro internalization efficiency and in vivo antitumor activity in each mutant was not consistent among different mutants, thus these results need to be interpreted cautiously. Citation Format: Atsushi Yamasaki, Misa Ikuta, Manabu Abe, Tsuneo Deguchi, Yasuki Kamai, Kenji Nakamaru, Toshinori Agatsuma. Pleclinical investigation of T-DXd internalization and payload release in HER2 mutant non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5376.

Background: Antibody-drug conjugates (ADCs) such as trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) have transformed the treatment of metastatic breast cancer (MBC). However, ADC-related alopecia remains poorly characterized. The effectiveness of scalp cooling in this setting is also unclear. Here, we evaluated the incidence and patterns of alopecia in patients (pts) with MBC treated with T-Dx and SG explored the potential protective effect of cold cap use. Methods: We identified pts with MBC treated with ADCs between June 2014 to June 2024 at UCLA using institutional databases. Pts were included based on ICD-9/10 codes for MBC, documentation of ADC use, and keywords related to scalp cooling discussion/ use in provider notes. Data were extracted on alopecia prior to ADC initiation (baseline alopecia), cold cap use during treatment, and alopecia development during ADC therapy based on clinical notes, patient self-report, and photographic documentation. Pts were stratified by pre-treatment alopecia status and ADC regimen (T-DXd, SG, or both sequentially). Those with alopecia attributed to neo/adjuvant chemotherapy administered at least one year prior to diagnosis of MBC were considered to have no baseline alopecia. Descriptive analyses were conducted to explore associations. Results: A total of 103 pts with MBC received ADC; T-DXd (n = 39), SG (n = 38), or both sequentially (n = 26). Disease subtypes included HR+/HER2− (36.8%), HR+/HER2+ (13.6%), HR−/HER2+ (12.6%), and TNBC (36.8%). Median age at MBC diagnosis was 54 years (range 26-80), and median duration of ADC treatment was 6.3 months (range 0-52.5). In the T-DXd group, 10/39 (25.6%) pts had baseline alopecia. Of the 29 pts without baseline hair loss, 10 (34.5%) developed alopecia while others did not have clear documentation of hair loss. Overall, 7 (of 29) pts without baseline alopecia used cold caps (4 [57.1%] developed alopecia) and 22 did not (6 [27.3%] had hair loss). In the SG cohort, 12/38 (31.6%) pts had baseline alopecia. Among the other 26 pts, 12 (46.2%) developed hair loss. Cold caps were used in 3 pts (2 [66.6%] had alopecia); of the 23 who did not use cooling, 10 (43.5%) experienced hair loss. Among the 26 pts who received both ADCs sequentially, 11 (42.3%) had baseline alopecia. Of the remaining 15 pts, 6 (40%) developed hair loss (5 during SG, 1 during T-DXd). One patient used a cold cap and did not have alopecia; among the 14 pts who did not use cooling, 6 (42.9%) developed alopecia. Conclusions: Alopecia is a common treatment-related toxicity among pts with MBC treated with T-DXd and/or SG. In this study, scalp cooling during ADC therapy was infrequent and appeared to offer limited protection against ADC-related alopecia. These findings underscore the need to develop innovative strategies to reduce hair loss risk with currently approved ADCs, as well as need to develop novel ADCs that do not confer alopecia risk for pts with breast cancer. Citation Format: S. Alkassis, L. Zhang, E. Yang, M. Lipsyc-Sharf, K. McCann, N. McAndrew, A. Master, J. LaBarbera, M. Sedrak, N. Palaskas, K. Greene, M. Kuiper, J. Glaspy, D. Elashoff, R. Callahan, A. Bardia. Alopecia Associated with Antibody-Drug Conjugates and Impact of Cold Caps For Patients with Breast Cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-01-20.

Antibody-drug conjugates (ADCs) offer a way to deliver a cytotoxic or an immuno-stimulatory payload directly to tumors to maximize the anti-tumor efficacy of the payload with reduced systemic toxicities. Over several decades, the development of ADCs has cycled through highs and lows in which substantial excitement over the promise of ADCs was followed by disinterest when disappointing clinical results were announced. This has resulted in several companies abandoning their internal ADC development efforts. To date, 13 ADCs have been approved to treat hematologic or solid tumors, with 11 granted FDA approvals. Several ADC deals have been announced, which has reinvigorated interest and investments in ADCs. The renewed interest in ADCs is due, in part, to the recent clinical success of Daiichi Sankyo’s HER2-targeting ADC, trastuzumab deruxtecan (Enhertu®; Daiichi Sankyo/AstraZeneca), which uses their proprietary topoisomerase I inhibitor payload, DXd. Enhertu is the first ADCs to gain US Food and Drug Administration’s (FDA) approval as a tissue-agnostic ADC, which provides optimism that more ADCs will be able to follow the success of trastuzumab deruxtecan.

Background: Antibody-drug conjugates (ADCs) such as trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) have revolutionized breast cancer (BC) treatment, providing superior efficacy that allows for extended treatment durations. Nausea and vomiting (NV) are among the most frequent adverse effects associated with T-DXd and SG, with nausea rates of >70% for T-DXd and >60% for SG in BC clinical trials. According to antiemetic guidelines, patients receiving T-DXd and SG are at moderate-to-high risk for NV and should routinely receive prophylaxis with an NK1 receptor antagonist (RA)-containing regimen. With limited real-world data on antiemetic efficacy in the ADC setting, a survey of international healthcare providers (HCPs) was conducted to assess their experience. Methods: At SABCS 2024, HCPs completed a brief web-based survey to assess their experiences and perceptions of ADC emetogenicity and approaches to antiemetic prophylaxis. Target participants included HCPs familiar with ADCs who manage patients with BC. Eligible participants completed the survey on computers located in the exhibit hall. Results: Of 209 HCPs surveyed, 112 were eligible. Most were oncologists (69%) or hematologist/oncologists (21%) who spent 73% of time in patient care; nearly half were US-based (46%). Among all HCPs, 80% reported using ADCs in practice and/or in clinical trials; 99% had experience with T-DXd and 87% with SG. Among HCPs using T-DXd and SG, 78% and 83%, respectively, perceived them as either highly (32% and 28%) or moderately (46% and 55%) emetogenic. NV reported by HCPs in this survey was much lower than in the T-DXd and SG clinical trials; HCPs reported that 30%, 25% and 15% of their BC patients treated with T-DXd experience N and/or V during the acute (0-24 hours), delayed (days 2-5), and long-delayed (beyond day 5) phases, respectively. Similarly, the reported NV rates were 29%, 26% and 13%, respectively, for SG. HCPs reported that 88% of patients treated with any ADCs in an average month receive antiemetic prophylaxis; however, only 39% of HCPs report exclusively using a guideline-recommended NK1 RA regimen with T-DXd or SG. The majority of HCPs (94%) reported implementing some type of dose adjustments of ADCs due to NV. A third to nearly half of HCPs had at least sometimes implemented an ADC dose reduction or delay due to NV while a quarter reported interrupting or discontinuing ADC treatment (Table). More than half reported using rescue medication at least sometimes for delayed NV. Conclusions: This survey highlights a gap between evidence and HCP perceptions regarding NV with T-DXd and SG, and reveals higher-than-expected dose reductions, likely reflecting suboptimal adherence to antiemetic guidelines. As ADCs gain prominence in BC treatment, these findings underscore the need for education and guideline-implementation to optimize NV prevention. Citation Format: L. S. Schwartzberg, L. Licata, G. Bianchini, Y. H. Park, E. J. Roeland, M. Massagrande, F. Dato, H. Iihara, F. Scotte, K. Jordan, M. Aapro, H. S. Rugo. Examining Antiemetic Management with Antibody-Drug Conjugates (ADCs) in Patients with Breast Cancer: Healthcare Provider (HCP) Insights from a SABCS Survey [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-01-13.

Antibody-drug conjugates (ADCs) are anticancer drugs that combine cytotoxic small-molecule drugs (payloads) with monoclonal antibodies through a chemical linker and that transfer toxic payloads to tumor cells expressing target antigens. All ADCs are based on human IgG. In 2009, the Food and Drug Administration (FDA) approved gemtuzumab ozogamicin as the initial first-generation ADC. Since then, at least 100 ADC-related projects have been initiated, and 14 ADCs are currently being tested in clinical trials. The limited success of gemtuzumab ozogamicin has led to the development of optimization strategies for the next generation of drugs. Subsequently, experts have improved the first-generation ADCs and have developed second-generation ADCs such as ado-trastuzumab emtansine. Second-generation ADCs have higher specific antigen levels, more stable linkers and longer half-lives and show great potential to transform cancer treatment models. Since the first two generations of ADCs have served as a good foundation, the development of ADCs is accelerating, and third-generation ADCs, represented by trastuzumab deruxtecan, are ready for wide application. Third-generation ADCs are characterized by strong pharmacokinetics and high pharmaceutical activity, and their drug-to-antibody ratio mainly ranges from 2 to 4. In the past decade, the research prospects of ADCs have broadened, and an increasing number of specific antigen targets and mechanisms of cytotoxic drug release have been discovered and studied. To date, seven ADCs have been approved by the FDA for lymphoma, and three have been approved to treat breast cancer. The present review explores the function and development of ADCs and their clinical use in cancer treatment.

Antibody-Drug Conjugates in urothelial, prostate, and renal cell cancers: A review of current and emerging therapies.