anti-HER2 Antibody-drug Conjugate Research Articles

Efficacy and Safety of Anti-HER2 Antibody-Drug Conjugate Based Therapy in HER2 Positive Breast Cancer: A Meta-Analysis

Efficacy and Safety of Anti-HER2 Antibody-Drug Conjugate Based Therapy in HER2 Positive Breast Cancer: A Meta-Analysis

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs.

Simple SummaryA proportion of breast tumors bear the oncogenic transmembrane tyrosine kinase protein HER2. Even though therapies that target HER2 have changed the prognosis and quality of life of patients with HER2+ breast tumors, resistance to those therapies is still an important clinical problem. To improve the management of those tumors, a new category of antitumor agents, antibody-drug conjugates (ADCs), has emerged. These agents are created by linking a potent cytotoxic to an antibody that recognizes a membrane protein. Two anti-HER2 ADCs have been approved by the FDA for clinical use and several others are under development. The structure, mechanism of action, and resistance mechanisms to ADCs are reviewed in the present work, as well as potential strategies to overcome resistance to clinically approved anti-HER2 ADCs, including novel anti-HER2 ADCs.During recent years, a number of new compounds against HER2 have reached clinics, improving the prognosis and quality of life of HER2-positive breast cancer patients. Nonetheless, resistance to standard-of-care drugs has motivated the development of novel agents, such as new antibody-drug conjugates (ADCs). The latter are a group of drugs that benefit from the potency of cytotoxic agents whose action is specifically guided to the tumor by the target-specific antibody. Two anti-HER2 ADCs have reached the clinic: trastuzumab-emtansine and, more recently, trastuzumab-deruxtecan. In addition, several other HER2-targeted ADCs are in preclinical or clinical development, some of them with promising signs of activity. In the present review, the structure, mechanism of action, and potential resistance to all these ADCs will be described. Specific attention will be given to discussing novel strategies to circumvent resistance to ADCs.

Trastuzumab deruxtecan for HER2+ advanced breast cancer.

Trastuzumab deruxtecan (T-DXd, DS-8201), an anti-HER2 antibody-drug conjugate, has shown significant clinical benefits in HER2+ metastatic breast cancer patients. In the phase 2 DESTINY-Breast01 trial, T-DXd demonstrated an objective response of 60.9% and median progression-free survival of 16.4months, laying the foundation for accelerated approval in HER2+ metastatic breast cancer patients who have received two or more prior anti-HER2-based regimens in the metastatic setting. Moreover, T-DXd exhibited promising antitumor efficacy against HER2-low-expressing metastatic breast cancer. Its distinctive side effect was pneumonitis, with a 13.6% incidence. It is approved in the US with boxed warnings for interstitial lung disease and embryo-fetal toxicity. This review focuses on preclinical, pharmacokinetic and pharmacodynamic data on T-DXd and clinical evidence of its antitumor activity (both as monotherapy and in combination) and tolerability in metastatic breast cancer.

Antibody-drug conjugates: Smart chemotherapy delivery across tumor histologies.

As distinct cancer biomarkers have been discovered in recent years, a need to reclassify tumors by more than their histology has been proposed, and therapies are now tailored to treat cancers based on specific molecular aberrations and immunologic markers. In fact, multiple histology-agnostic therapies are currently adopted in clinical practice for treating patients regardless of their tumor site of origin. In parallel with this new model for drug development, in the past few years, several novel antibody-drug conjugates (ADCs) have been approved to treat solid tumors, benefiting from engineering improvements in the conjugation process and the introduction of novel linkers and payloads. With the recognition that numerous surface targets are expressed across various cancer histologies, alongside the remarkable activity of modern ADCs, this drug class has been increasingly evaluated as suitable for a histology-agnostic expansion of indication. For illustration, the anti-HER2 ADC trastuzumab deruxtecan has demonstrated compelling activity in HER2-overexpressing breast, gastric, colorectal, and lung cancer. Examples of additional novel and potentially histology-agnostic ADC targets include trophoblast cell-surface antigen 2 (Trop-2) and nectin-4, among others. In the current review article, the authors summarize the current approvals of ADCs by the US Food and Drug Administration focusing on solid tumors and discuss the challenges and opportunities posed by the multihistological expansion of ADCs.

Trastuzumab deruxtecan and other HER2-targeting agents for the treatment of HER2-positive gastric cancer

ABSTRACT Introduction Although various new drugs have been developed, the prognosis of therapeutic advances for metastatic gastric cancer is insufficient. Trastuzumab deruxtecan (T-DXd), a new human epidermal growth factor receptor 2 (HER2)-targeting antibody–drug conjugate (ADC), has demonstrated promising results in clinical trials. Areas covered In this article, we review the history of anti-HER2 ADCs and focus on the efficacy and safety of T-DXd and describe the development of new anti-HER2 drugs. Expert opinion So far, no other anti-HER2 ADCs have demonstrated efficacy in patients with HER2-positive advanced gastric cancer with two or more previous lines of chemotherapy, including trastuzumab. However, a new drug, T-DXd, has shown a significantly higher objective response rate and a longer overall survival and, thus, was approved in Japan. In the future, new anti-HER2 drugs and/or treatment strategies including T-DXd along with cytotoxic chemotherapy or immune checkpoint inhibitors will be developed.

Pyrotinib combined with thalidomide in advanced non-small-cell lung cancer patients harboring HER2 exon 20 insertions (PRIDE): protocol of an open-label, single-arm phase II trial

BackgroundStandard therapy for human epidermal growth factor receptor 2 (HER2)-mutant non-small-cell lung cancer (NSCLC) is lacking. The clinical benefits with pan-HER inhibitors (afatinib, neratinib, and dacomitinib), anti-HER2 antibody drug conjugate (ADC) trastuzumab emtansine, and an emerging irreversible tyrosine kinase inhibitor (TKI) poziotinib were modest. Another new ADC trastuzumab deruxtecan showed encouraging outcomes, but only phase I study was completed. Pyrotinib, another emerging irreversible epidermal growth factor receptor (EGFR)/HER2 dual TKI, has been approved in HER2-positive breast cancer in 2018 in China. It has shown promising antitumor activity against HER2-mutant NSCLC in phase II trials, but pyrotinib-related diarrhea remains an issue. The antiangiogenic and immunomodulatory drug thalidomide is a cereblon-based molecular glue that can induce the degradation of the IKAROS family transcription factors IKZF1 and IKZF3. The use of thalidomide can also decrease gastrointestinal toxicity induced by anti-cancer therapy.MethodsThis is an open-label, single-arm phase II trial. A total of 39 advanced NSCLC patients with HER2 exon 20 insertions and ≤ 2 lines of prior chemotherapy will be recruited, including treatment-naïve patients who refuse chemotherapy. Patients are allowed to have prior therapy with immune checkpoint inhibitors and/or antiangiogenic agents. Those who have prior HER2-targeting therapy or other gene alterations with available targeted drugs are excluded. Eligible patients will receive oral pyrotinib 400 mg once daily and oral thalidomide 200 mg once daily until disease progression or intolerable toxicity. The primary endpoint is objective response rate.DiscussionThe addition of thalidomide to pyrotinib is expected to increase the clinical benefit in advanced NSCLC patients with HER2 exon 20 insertions, and reduce the incidence of pyrotinib-related diarrhea. We believe thalidomide is the stone that can hit two birds.Trial registrationClinicalTrials.gov Identifier: NCT04382300. Registered on May 11, 2020.

1767P Co-clinical PDX study of trastuzumab deruxtecan in HER2-positive uterine carcinosarcoma (STATICE trial, NCCH1615)

Uterine carcinosarcoma (UCS) is a rare and highly aggressive disease, which has been categorized as a subtype of high-grade endometrial cancer but not uterine sarcoma. A high clinical efficacy of a novel anti-HER2 antibody drug conjugate, trastuzumab deruxtecan (T-DXd), in HER2-positive UCS will be reported at ESMO2021 (STATICE TRIAL). Herein, we report a co-clinical study of T-DXd using patient-derived xenograft (PDX) models of patients that participated in the STATICE trial.

212P HER2-low breast cancer: Evolution from primary tumor to residual disease after neoadjuvant treatment

Approximately a half of breast tumors traditionally classified as HER2-neg exhibit HER2-low expression (IHC 1+ or 2+ and ISH neg.). We recently described a high instability of HER2-low expression from primary breast cancer (BC) to relapse (Miglietta F et al., ESMO Breast Cancer 2021). Aim of this study is to track the evolution of HER2-low expression from primary BC to residual disease (RD) after neoadjuvant treatment. Patients undergoing neoadjuvant treatment with available baseline tumor tissue and matched samples of RD (in case of no pCR) were included. HER2 expression was evaluated according to ASCO/CAP recommendations in place at the time of diagnosis. Cases diagnosed between 2007 and 2013 were reviewed to comply with the 10% cutoff of IHC for HER2-positivity. HER2-neg cases were further classified as HER2-0 or HER2-low (IHC 1+ or 2+ and ISH neg.). 447 patients were included. Primary BC phenotype was: HR-pos/HER2-neg 23%, triple-negative (TN) 35%, HER2-pos 42%. HER2-low cases were 56% of the HER2-neg cohort and were significantly enriched in the HR-pos/HER2-neg vs TN subgroup (69% vs 47%, p=0.001). In patients failing to achieve pCR after neoadjuvant treatment (n=292), the overall rate of HER2 expression discordance was 27%, mostly driven by cases converting either from HER2-0 primary BC to HER2-low RD (9%) or from HER2-low primary BC to HER2-0 RD (15%; Table). Overall, 36% of non-pCR patients had a HER2-low expression on RD, including 12% of patients with TN and 24% of patients with HR-pos/HER2-neg disease. Among HR-pos/HER2-neg patients with HER2-low expression on RD, 23% had an estimated high risk of relapse according to the residual proliferative cancer burden (RPCB class 3).Table: 212PPrimary tumorResidual diseaseHER2-0HER2-lowHER2-posTotaln%n%n%n%HER2-05117269007726HER2-low431570241<111439HER2-pos0083933210135Total9432104369432292100 Open table in a new tab HER2-low expression showed high instability from primary BC to RD after neoadjuvant treatment. HER2-low expression on RD may guide personalized adjuvant treatment for high-risk patients in the context of clinical trials with novel anti-HER2 antibody-drug conjugates.

HER2: a never ending story.

Access to anti-HER2 agents for breast cancer is restricted to patients with HER2-positive tumours. However, the promising activity of novel anti-HER2 antibody–drug conjugates in patients with tumours with HER2-low-positive expression 1 Modi S Park H Murthy RK et al. antitumor activity and safety of trastuzumab deruxtecan in patients with HER2-low-expressing advanced breast cancer: results from a phase Ib study. J Clin Oncol. 2020; 38: 1887-1896 Google Scholar , 2 Banerji U van Herpen CML Saura C et al. Trastuzumab duocarmazine in locally advanced and metastatic solid tumours and HER2-expressing breast cancer: a phase 1 dose-escalation and dose-expansion study. Lancet Oncol. 2019; 20: 1124-1135 Google Scholar is challenging the dichotomy of HER2-positive versus HER2-negative breast cancer. Clinical and molecular characteristics of HER2-low-positive breast cancer: pooled analysis of individual patient data from four prospective, neoadjuvant clinical trialsOur results show that HER2-low-positive tumours can be identified as new subgroup of breast cancer by standardised IHC, distinct from HER2-zero tumours. HER2-low-positive tumours have a specific biology and show differences in response to therapy and prognosis, which is particularly relevant in therapy-resistant, hormone receptor-negative tumours. Our results provide a basis for a better understanding of the biology of breast cancer subtypes and the refinement of future diagnostic and therapeutic strategies. Full-Text PDF

Clinical and molecular characteristics of HER2-low-positive breast cancer: pooled analysis of individual patient data from four prospective, neoadjuvant clinical trials.

The development of anti-HER2 antibody-drug conjugates opens new therapeutic options for patients with breast cancer, including patients with low expression of HER2. To characterise this new breast cancer subtype, we have compared the clinical and molecular characteristics of HER2-low-positive and HER2-zero breast cancer, including response to neoadjuvant chemotherapy and prognosis. In this pooled analysis of individual patient data, we evaluated a cohort of 2310 patients with HER2-non-amplified primary breast cancer that were treated with neoadjuvant combination chemotherapy in four prospective neoadjuvant clinical trials (GeparSepto, NCT01583426; GeparOcto, NCT02125344; GeparX, NCT02682693; Gain-2 neoadjuvant, NCT01690702) between July 30, 2012, and March 20, 2019. Central HER2 testing was done prospectively before random assignment of participants in all trials. HER2-low-positive status was defined as immunohistochemistry (IHC) 1+ or IHC2+/in-situ hybridisation negative and HER2-zero was defined as IHC0, based on the American Society of Clinical Oncology/College of American Pathologists guidelines. Disease-free survival and overall survival data were available for 1694 patients (from all trials except GeparX) with a median follow-up of 46·6 months (IQR 35·0-52·3). Bivariable and multivariable logistic regression models and Cox-proportional hazards models were performed based on a predefined statistical analysis plan for analysis of the endpoints pathological complete response, disease-free survival, and overall survival. A total of 1098 (47·5%) of 2310 tumours were HER2-low-positive and 1212 (52·5%) were HER2-zero. 703 (64·0%) of 1098 patients with HER2-low-positive tumours were hormone receptor positive, compared with 445 (36·7%) of 1212 patients with HER2-zero tumours (p<0.0001). HER2-low-positive tumours had a significantly lower pathological complete response rate than HER2-zero tumours (321 [29·2%] of 1098 vs 473 [39·0%] of 1212, p=0·0002). Pathological complete response was also significantly lower in HER2-low-positive tumours versus HER2-zero tumours in the hormone receptor-positive subgroup (123 [17·5%] of 703 vs 105 [23·6%] of 445, p=0·024), but not in the hormone receptor-negative subgroup (198 [50·1%] of 395 vs 368 [48·0%] of 767, p=0·21). Patients with HER2-low-positive tumours had significantly longer survival than did patients with HER2-zero tumours (3-year disease-free survival: 83·4% [95% CI 80·5-85·9] vs 76·1% [72·9-79·0]; stratified log-rank test p=0·0084; 3-year overall survival: 91·6% [84·9-93·4] vs 85·8% [83·0-88·1]; stratified log-rank test p=0·0016). Survival differences were also seen in patients with hormone receptor-negative tumours (3-year disease-free survival: 84·5% [95% CI 79·5-88·3] vs 74·4% [70·2-78.0]; stratified log-rank test p=0·0076; 3-year overall survival: 90·2% [86·0-93·2] vs 84·3% [80·7-87·3], stratified log-rank test p=0·016), but not in patients with hormone receptor-positive tumours (3-year disease-free survival 82·8% [79·1-85·9] vs 79·3% [73·9-83·7]; stratified log-rank test p=0·39; 3-year overall survival 92·3% [89·6-94·4] vs 88·4% [83·8-91·8]; stratified log-rank test p=0·13). Our results show that HER2-low-positive tumours can be identified as new subgroup of breast cancer by standardised IHC, distinct from HER2-zero tumours. HER2-low-positive tumours have a specific biology and show differences in response to therapy and prognosis, which is particularly relevant in therapy-resistant, hormone receptor-negative tumours. Our results provide a basis for a better understanding of the biology of breast cancer subtypes and the refinement of future diagnostic and therapeutic strategies. German Cancer Aid (Deutsche Krebshilfe).

Abstract 945: Trastuzumab deruxtecan (T-DXd) sensitivity in various levels of HER2 expressing gastric cancer cells

Abstract Trastuzumab, a humanized anti-HER2 monoclonal antibody, has shown clinically significant benefits for HER2-positive GC patients. Also, all anti-HER2 agents approved by the FDA are used for HER2-positive. However, since HER2-positive is only 10-20% of GC, targeted therapies for non-HER2-positive GC is needed. To overcome these limitations, antibody-drug conjugates (ADCs), which directly deliver cytotoxic drugs to cancer cells, have been developed. T-DXd (Daiichi Sankyo, Japan), an anti-HER2 ADC, can induce the death of neighboring cells because it has a bystander killing effect due to the high membrane permeability of the payload. However, biomarkers for predicting drug response have not yet been studied other than HER2 overexpression/amplification. In this study, we investigated the correlation between HER2 expression level and anti-tumor effect of T-DXd in a 49 GC cell line panel and the HER2-associated molecules related to T-DXd sensitivity. For HER2 status, we analyzed multiple genetic and molecular characteristics using WES, SISH, IHC, flow cytometry, and immunoblotting. GC cell lines (n=49) were divided into 3 groups according to the HER2 expression level through flow cytometry using 4 breast cancer cell lines (SK-BR-3, ZR-75-1, MCF-7, and HCC1937) for quantitative control. Groups with HER2 over- and moderate/low-expression were characterized with higher expression levels compared to ZR-75-1 (HER2 2+) and HCC1937 (HER2-negative), respectively. HER2 non-expression had lower expression levels compared to HCC1937. The sensitivity of T-DXd was evaluated in 49 GC cell lines by cell viability assay. The inhibition rate of T-DXd was calculated at 10 µg/ml. Also, expression levels of RTKs were determined by immunoblotting, and HER2 extracellular domain (ECD) and NRG1 expression were evaluated by ELISA. GC cell lines were divided into 6 HER2 over-, 26 HER2 moderate/low-, and 17 HER2 non-expression cell lines. As expected, HER2 over-expression cell lines were sensitive to T-DXd (5/6, 83.3%). T-DXd also had anti-tumor effects in the HER2 moderate/low-expression cell lines (12/26, 46.2%). There were correlations between HER2 expression level and anti-tumor effect of T-DXd in both HER2 over and moderate/low-expression cell lines. HER2 over and moderate/low-expression cell lines with high HER2 ECD expression were sensitive to T-DXd. NRG1 had relatively low expression in all GC cell lines and was not correlated with T-DXd. Additionally, even HER2 non-expression cell lines were sensitive to T-DXd (10/17, 58.8%). We found that HER2 non-expression cell lines had an RTK amplification (9/17, 52.9%) and among those cell lines, MET amplified cells showed sensitivity to T-DXd. Currently, the evaluation of the underlying mechanisms is ongoing. Our results indicate that T-DXd shows efficacy in HER2-amplified GC cell lines, HER2 moderate/low-expression, and some cell lines with HER2 non-expression. Citation Format: Seo Young Yu, Juin Park, Woo Sun Kwon, Inhye Jeong, Sun Kyoung Kang, Hyun Joo Bae, Tae Soo Kim, Hyun Cheol Chung, Sun Young Rha. Trastuzumab deruxtecan (T-DXd) sensitivity in various levels of HER2 expressing gastric cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 945.

An open-label, single-arm, multicenter, phase II study of RC48-ADC to evaluate the efficacy and safety of subjects with HER2 overexpressing locally advanced or metastatic urothelial cancer (RC48-C009).

4584 Background: There is still urgent medical needs in the patients with locally advanced or metastatic urothelial cancer (mUC) post to the failure of at least one line chemotherapy. RC48-ADC, a novel humanized anti-HER2 antibody-drug conjugate (ADC), has proved its efficacy in these patients (RC48-C005, NCT03507166), most of whom had received gemcitabine and platinum. Taking into consideration that taxane is another possible active agent for mUC, this study aims to further evaluate the efficacy of RC48-ADC in HER2 overexpressing mUC post to the failure of platinum, gemcitabine and taxane. Methods: This study was an open-label, multicenter, single-arm, non-randomized phase II study. Eligibility criteria included: histologically confirmed UC, HER2 overexpressing (IHC 2+ or 3+), ECOG PS 0-1, failed platinum, gemcitabine and taxane. The patients received RC48-ADC treatment alone (2 mg/kg IV infusion, q2w) until disease progression, unacceptable toxicity, withdrawal, death or study termination. The primary endpoint was objective response rate (ORR) assessed by blinded independent review committee (BIRC) according to RECIST v1.1. Progress-free survival (PFS), duration of response (DOR), overall survival (OS), and safety was also assessed. Results: Patient enrollment for this study started in December 2018 and completed in September 2020. A total of 64 patients were enrolled, with a median age of 62.5 years. At baseline, most patients (82.8%) had visceral metastasis. Fifty-five patients (85.9%) had received ≥ 2 lines treatment and 19 (29.7%) patients had prior immune checkpoint inhibitor (CPI) therapy. As of Nov 30, 2020, the confirmed ORR assessed by BIRC was 46.9% (95% CI: 34.3%, 59.8%) and the median DOR was 8.3 months (95% CI: 4.3, NE), the median PFS was 4.3 months (95% CI: 4.0, 6.8). The median OS was 14.8 months (95% CI: 8.7, 21.1). The ORR was 60.0% (15/25) in patients with HER2 IHC3+ or FISH test positive, 45.3% (24/53) in patients with visceral metastasis, 42.1% (8/19) in patients post to CPI therapy. The ORR was 55.6% (5/9), 50.0% (21/20) and 30.8% (4/13), in patients who had received 1 line, 2 lines and ≥ 3 lines treatment, respectively. Most commonly reported TRAEs were leukopenia (45.3%), AST increase (43.8%), neutropenia (42.2%), hypoesthesia (42.2%), ALT increase (37.5%) and fatigue (35.9%); Most commonly reported ≥ grade 3 TRAEs were neutropenia (9.4%) and hypoesthesia (6.3%) Conclusions: In patients with HER2 overexpressing (IHC 2+ or 3+) mUC who had failed platinum, gemcitabine and taxane, and the great majority of whom had received ≥2 prior lines treatment, RC48-ADC has demonstrated consistently excellent efficacy and benefit-risk profile compared with the RC48-C005 study which enrolled patients with mUC who had received ≥1 line prior chemotherapy. Clinical trial information: NCT03809013.

RC48-ADC combined with toripalimab, an anti-PD-1 monoclonal antibody (Ab), in patients with locally advanced or metastatic urothelial carcinoma (UC): Preliminary results of a phase Ib/II study.

4534 Background: RC48-ADC is a novel humanized anti-HER2 antibody-drug conjugate (ADC), which showed promising data in HER2-positive and even negative patients (pts). Anti-PD-1 Abs have durable antitumor effect for mUC especially in PD-L1 positive patients. The combination may have synergistic antitumor effect. This phase 1b/II study evaluated the safety and activity of RC48-ADC combined with toripalimab in mUC. Methods: In dose-escalation cohort, pts received 1.5 or 2 mg/kg RC48-ADC + 3mg/kg toripalimab with the traditional 3+3 escalation design. In expansion cohort, patients received the recommended dose of RC48-ADC + toripalimab every 2 weeks. The primary endpoints were safety/tolerability and recommended RC48-ADC dose; secondary endpoints included pharmacokinetics, ORR per RECIST 1.1, PFS, and OS stratified by HER2 and PD-L1 expression. HER2 positivity was determined by IHC and in situ hybridization (ISH). PD-L1 expression was tested with IHC 22C3 pharmDx assay. Results: As of 8 Jan 2021 (data cutoff), 14 mUC pts (9 males, median age 66 y [52-76]) were enrolled. Most pts were systemic treatment naïve (57%) in the locally advanced or metastatic setting. The primary site was in upper tract UC in 50%; 50% had visceral metastases (mets), including 36% with liver mets; HER2 expression was positive (IHC 3+ or 2+ ISH+) in 28%, and 43% PD-L1 CPS≥10. A total of 36 pts is anticipated to be enrolled by Apr 2021. No dose limiting toxicity was reported and the recommended dose for RC48-ADC was 2mg/kg. At data cutoff, 10/14 patients were evaluable for response, with 8 PR, 1 SD (tumor shrinking), and 1 PD. The objective response rate (ORR) was 80%, and disease control rate (DCR) was 90%. All responsive patients have durable efficacy and are still on treatment. Follow-up continues for PFS and OS. Most common treatment-related AEs were grade 1-2, including aminotransferase level increased (7/14, 50%), weight loss (6/14, 43%), alopecia (6/14, 43%), asthenia (4/14, 29%), anemia (3/14, 21%), leukopenia (21%), peripheral sensory neuropathy (21%), hypothyroidism (21%), blood triglycerides increased (21%), and creatine phosphokinase increase (21%). One pt had G3 intestinal obstruction attributed to study drug and went back to treatment after recovery. Conclusions: RC48-ADC in combination with toripalimab had a good tolerance and promising anti-tumor activity in pts with mUC. Further evaluation of safety and efficacy is ongoing. Clinical trial information: NCT04264936.

The association of HER2 low expression with the efficacy of CDK4/6 inhibitor in hormone receptor positive HER2 negative metastatic breast cancer.

1052 Background: Markers for the efficacy of CDK4/6 inhibitor in estrogen receptor (ER) positive, HER2 negative advanced breast cancer are limited. The bidirectional crosstalks that exist between ER and HER2 pathways contribute to endocrine resistance. We investigated the association between low levels of HER2 expression and the clinical outcome of patients with ER+ HER2- metastatic breast cancer (MBC) treated with CDK4/6 inhibitors. Methods: We identified consecutive patients with ER+ HER2- MBC who received CDK4/6 inhibitor plus either letrozole or fulvestrant between Mar 2017 - Jun 2020 from an institutional cancer registry. HER2-low expression was defined as IHC score 1+, or 2+ with a negative ISH. Progression-free survival (PFS) was defined as the time from the initiation of CDK4/6 inhibitor to the date of radiological or clinical progression, or death. The relationship between HER2 expression levels and PFS was evaluated using log-rank test and multivariable Cox regression modelling. Results: 106 women with MBC were eligible for analysis. Median age at treatment was 58 (23.0-91.4). The majority received palbociclib (84%) while the rest received ribociclib. CDK4/6 inhibitor was used as first-line treatment in 50.9% of cases. Most tumors were of ductal histology (83%) and progesterone receptor (PgR) positive (84.9%), and 22.6% of the patients had bone-only disease. 77.3% of cases were considered HER2-low expressing. HER2-low expression was associated with a significantly shorter PFS compared with HER2 IHC 0 counterpart (median, 8.9 vs 18.8 months, p= 0.014). In multivariate analysis, HER-2 low expression remained significantly associated with an inferior PFS (HR 1.96, 95%CI 1.03-3.75, p= 0.041) after adjusting for the line of treatment, PgR status and disease extent (bone only vs extra-osseous disease). Conclusions: In patients with ER+ HER2- MBC treated with CDK4/6 inhibitors, HER2-low expression was associated with an inferior PFS, and may serve as a potential marker candidate for CDK4/6 inhibitor efficacy. As novel anti-HER2 antibody-drug conjugates demonstrated efficacy in HER2-low expressing MBC, coupled with the emerging evidence for the combination of CDK4/6 inhibitors with anti-HER2 agents, this HER2-low expression subgroup warrants prospective evaluations in future trials.

Abstract OT-03-07: Solti-1804 HER2-PREDICT: A biomarker research study of DS8201-A-U301 -U302 and -U303 trials

Abstract Background: Overexpression of human epidermal growth factor receptor 2 (HER2) occurs in 15-20% of breast cancers (BC). At the same time, HER2-low tumors (immunohistochemistry 1+ or 2+ with no gene amplification) comprise ~50% of all BC. DS-8201a is an anti-HER2 antibody drug conjugate that has shown very promising response rates both in HER2+ and HER2low BC. However, not all patients respond or benefit to the same extend. Thus, there is a need to identify predictive biomarkers. Here, we hypothesize that by performing several molecular studies in both tissue and plasma samples of those patients participating in the pivotal DESTINY-Breast trials, we will shed more light about the molecular features of HER2+ BC and better characterized the patient population according to their benefit from this promising new anti-HER2 agent. Methods: HER2-PREDICT is a multi-center, observational study within the biomarker program of SOLTI group, which will include patients who will participate, are participating or previously participated in the Daiichi Sankyo INC sponsored phase III trials: DS8201-A-U301 (NCT03523585), -U302 (NCT03529110) and -U303 (NCT03734029). Patients with HER2-positive or HER2-low unresectable and/or metastatic breast cancer may be included in SOLTI-1804 HER2-PREDICT study if randomized to the DS-8201a arm. All patients need to consent for obtaining a fresh tumor biopsy or donating an archival metastatic biopsy. Primary tumors are allowed under SOLTI acceptance. Additionally, patients included before initiating DS-8201a therapy will provide blood samples for biomarker analyses on Cycle 1 Day 1 (C1D1), C2D1 and end of treatment. The primary objectives are (1) to identify an optimal ERBB2 mRNA cut-off point predictive of Ds-8201a response and (2) to evaluate the correlation of baseline ERBB2 mRNA levels (as a continuous variable) with overall response rate (ORR) in the Ds-8201a-treated cohorts. Secondary objectives includes: to evaluate the association of ERBB2 mRNA levels, PAM50 intrinsic subtypes and immune-related genes with ORR, progression-free survival and overall survival; to design a new gene expression signature predictive of Ds-8201a benefit; to correlate early changes in ctDNA with Ds-8201a benefit and to identify acquired somatic mutations of resistance to DS8201a upon progression in plasma samples. Collection of tumor biopsies is an essential part of this study. Pathological analysis includes hematoxylin and eosin (H&amp;E) staining, identification of areas with greater amount of tumor cells and determination of their tumor cell percentage. RNA will be isolated and analyzed at the nCounter (Nanostring Technologies). Molecular intrinsic subtypes will be identified by a research-based version of PAM50. Furthermore, we aim to evaluate 771 additional genes (+5 housekeeping genes) that encompass important genomic signatures and individual genes of importance for breast cancer by means of the nCounter®Breast Cancer 360 Panel. Somatic mutations in PIK3CA, TP53, and additional genes (e.g., GATA3 and ERBB2) will be identified using next-generation sequencing (NGS). Also, a comprehensive NGS gene panel will be performed under the Ion Torrent or Illumina platforms to DNA extracted from FFPE tumor blocks and to circulating tumor DNA (ctDNA) in plasma samples. Current status: Since December 13th, 2019, a total of 10 patients have been included, 5 of them with blood samples. As of today, 13 out of 15 Spanish sites are recruiting patients. Clinical trial identification: NCT04257162 Citation Format: Aleix Prat, Joaquin Gavilá, Sonia Pernas, Josefina Cruz, Cristina Saura, Esteban Nogales, Maria Bermejo, Javier Salvador Bofill, Vanesa Quiroga, Laura Garcia-Estévez, Serafin Morales, Sonia Servitja, Rubén del Toro, Patricia Galván, Núria Chic, Débora Martinez, Fara Brasó-Maristany, Jordi Canes, Laia Paré, Juan M Ferrero-Cafiero, Patricia Villagrasa. Solti-1804 HER2-PREDICT: A biomarker research study of DS8201-A-U301 -U302 and -U303 trials [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-03-07.

Targeting HER2 Alterations in Non-Small-Cell Lung Cancer: A Comprehensive Review.

HER2 is a critical gene that drives various solid tumors in addition to those of breast cancer. For example, HER2 plays a role in non-small-cell lung cancer (NSCLC). Overexpression, amplification, and point mutations in HER2 have been described in patients with NSCLC; however, the potential roles of these alterations remain unclear. We summarize the evidence regarding the distinct impacts of different HER2 aberrations on antitumor agents. Also, we update the therapeutic efficacy of HER2-targeted agents, including anti-HER2 antibodies, antibody-drug conjugates, and small-molecule tyrosine kinase inhibitors, tested in HER2-aberrant NSCLC. Although these drugs are not yet standard treatments, certain patients may benefit from these therapies. In this review, we aim to provide an improved understanding of HER2 aberrations in NSCLC, including NSCLC biology and the impacts of each aberration on prognosis and standard treatment. We also highlight the potential of novel anti-HER2 therapies approved by regulatory bodies and those in clinical development. Compared with HER2 amplification or overexpression, HER2 mutations, especially HER2 exon 20 mutations, are emerging as the most clear targetable driver for HER2-directed therapies in lung cancer. De novo and inducible HER2 pathway activation need to be differentially managed. Further investigations with new strategies are needed.

PF-06804103, A Site-specific Anti-HER2 Antibody-Drug Conjugate for the Treatment of HER2-expressing Breast, Gastric, and Lung Cancers.

The approval of ado-trastuzumab emtansine (T-DM1) in HER2+ metastatic breast cancer validated HER2 as a target for HER2-specific antibody-drug conjugates (ADC). Despite its demonstrated clinical efficacy, certain inherent properties within T-DM1 hamper this compound from achieving the full potential of targeting HER2-expressing solid tumors with ADCs. Here, we detail the discovery of PF-06804103, an anti-HER2 ADC designed to have a widened therapeutic window compared with T-DM1. We utilized an empirical conjugation site screening campaign to identify the engineered ĸkK183C and K290C residues as those that maximized in vivo ADC stability, efficacy, and safety for a four drug-antibody ratio (DAR) ADC with this linker-payload combination. PF-06804103 incorporates the following novel design elements: (i) a new auristatin payload with optimized pharmacodynamic properties, (ii) a cleavable linker for optimized payload release and enhanced antitumor efficacy, and (iii) an engineered cysteine site-specific conjugation approach that overcomes the traditional safety liabilities of conventional conjugates and generates a homogenous drug product with a DAR of 4. PF-06804103 shows (i) an enhanced efficacy against low HER2-expressing breast, gastric, and lung tumor models, (ii) overcomes in vitro- and in vivo-acquired T-DM1 resistance, and (iii) an improved safety profile by enhancing ADC stability, pharmacokinetic parameters, and reducing off-target toxicities. Herein, we showcase our platform approach in optimizing ADC design, resulting in the generation of the anti-HER2 ADC, PF-06804103. The design elements of identifying novel sites of conjugation employed in this study serve as a platform for developing optimized ADCs against other tumor-specific targets.

ARX788, a Site-specific Anti-HER2 Antibody-Drug Conjugate, Demonstrates Potent and Selective Activity in HER2-low and T-DM1-resistant Breast and Gastric Cancers.

First-generation antibody-drug conjugates (ADC) are heterogeneous mixtures that have shown clinical benefit, but generally exhibited safety issues and a narrow therapeutic window due, in part, to off-target toxicity caused by ADC instability. ARX788 is a next-generation, site-specific anti-HER2 ADC that utilizes a unique nonnatural amino acid-enabled conjugation technology and a noncleavable Amberstatin (AS269) drug-linker to generate a homogeneous ADC with a drug-to-antibody ratio of 1.9. ARX788 exhibits high serum stability in mice and a relatively long ADC half-life of 12.5 days. When compared in vitro against T-DM1 across a panel of cancer cell lines, ARX788 showed superior activity in the lower HER2-expressing cell lines and no activity in normal cardiomyocyte cells. Similarly, ARX788 significantly inhibited tumor growth, and generally outperformed T-DM1 in HER2-high and HER2-low expression xenograft models. Breast and gastric cancer patient-derived xenograft studies confirmed strong antitumor activity of ARX788 in HER2-positive and HER2-low expression tumors, as well as in a T-DM1-resistant model. The encouraging preclinical data support the further development of ARX788 for treatment of patients with HER2-positive breast and gastric cancer, including those who have developed T-DM1 resistance, and patients with HER2-low expression tumors who are currently ineligible to receive HER2-targeted therapy.

The role of ado-trastuzumab emtansine in current clinical practice.

This review reflects the literature from 2019 to 2020 on ado-trastuzumab emtansine's (T-DM1) therapeutic use, clinical controversies, and newest perspectives on use.Data sources: PubMed was used as a database. Search "ado-trastuzumab emtansine" on June 11th, 2020 resulted in 57 publications: 20 clinical trials, two metanalysis, six randomized controlled studies, 13 reviews, and two systematic reviews. Of the 57 publications, 34 were descriptive of the topic in question and were used for this review.Data summary: T-DM1 is now used for patients with HER2 breast cancer who have residual disease post surgery after neoadjuvant chemotherapy (KATHERINE trial). Initial success prompted KRISTINE trial, which investigated whether T-DM1 can be used as a neoadjuvant therapy. While it did have fewer adverse events, T-DM1 was inferior to chemotherapy in treating early breast cancer. Noted shortcomings of the drug were toxicity limited Cmax, slow rate of internalization, lack of payload bystander effects, and number of resistance mechanisms. Proposed solutions were pre-treatment with metformin to augment drug internalization by the cell, use of second generation anti-HER2 antibody-drug conjugates to overcome developing resistance, payload swapping to increase bystander effect. While T-DM1 has fewer side-effects, it is inferior to chemotherapy in early breast cancer treatment. More research should be done to overcome resistance pathways, identify rate-limiting intracellular processing pathways, improve bystander, and enhance internalization of the drug. Until more research is done, T-DM1 will continue to be used in HER2 positive breast cancer as well as a few other HER2 expressing tumors that fail to respond to neoadjuvant therapy.

Improving Receptor-Mediated Intracellular Access and Accumulation of Antibody Therapeutics-The Tale of HER2.

Therapeutic anti-HER2 antibodies and antibody–drug conjugates (ADCs) have undoubtedly benefitted patients. Nonetheless, patients ultimately relapse—some sooner than others. Currently approved anti-HER2 drugs are expensive and their cost-effectiveness is debated. There is increased awareness that internalization and lysosomal processing including subsequent payload intracellular accumulation and retention for ADCs are critical therapeutic attributes. Although HER2 preferential overexpression on the surface of tumor cells is attractive, its poor internalization and trafficking to lysosomes has been linked to poor therapeutic outcomes. To help address such issues, this review will comprehensively detail the most relevant findings on internalization and cellular accumulation for approved and investigational anti-HER2 antibodies and ADCs. The improved clarity of the HER2 system could improve antibody and ADC designs and approaches for next-generation anti-HER2 and other receptor targeting agents.