Efficacy Of T-DM1 Research Articles

Disitamab vedotin in preclinical models of HER2-positive breast and gastric cancers resistant to trastuzumab emtansine and trastuzumab deruxtecan.

Most HER2-positive breast or gastric cancers eventually become resistant to the approved anti-HER2 antibody-drug conjugates (ADC) trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd). Disitamab vedotin (DV) is a novel anti-HER2 ADC that binds to a different epitope on HER2 compared to trastuzumab. We assessed the efficacy of DV in breast and gastric cancer cell lines and xenografts, including tumor models resistant to T-DM1 and T-DXd. Additionally, we investigated whether combining two anti-HER2 ADCs could enhance the efficacy of the individual ADCs. The efficacy of DV, T-DM1, and T-DXd, both as single agents and in combinations, was assessed using an AlamarBlue cell proliferation assay in HER2-positive breast and gastric cancer cell lines, including those resistant to T-DM1 and T-DXd. The efficacy of DV was evaluated also in breast and gastric cancer SCID mouse xenografts that had progressed on T-DM1 and/or T-DXd. ADC combinations were tested in breast and gastric cancer xenografts. DV was effective in cell lines resistant to T-DM1 and/or T-DXd, and it inhibited the growth of breast and gastric cancer xenografts that had progressed on T-DM1 and/or T-DXd. The combinations of DV plus T-DM1 and DV plus T-DXd showed greater efficacy than the corresponding single agents in both breast and gastric cancer cell lines and xenografts. DV was effective in treating breast and gastric cancer xenograft tumors resistant to T-DM1 and/or T-DXd. The combination of DV with T-DM1 or T-DXd demonstrated promising activity.

Pre-Clinical Rationale for Amcenestrant Combinations in HER2+/ER+ Breast Cancer.

HER2-positive/oestrogen receptor-positive (HER2+/ER+) represents a unique breast cancer subtype. The use of individual HER2- or ER-targeting agents can lead to the acquisition of therapeutic resistance due to compensatory receptor crosstalk. New drug combinations targeting HER2 and ER could improve outcomes for patients with HER2+/ER+ breast cancer. In this study, the pre-clinical rationale is explored for combining amcenestrant (Amc), a selective oestrogen receptor degrader (SERD), with HER2-targeted therapies including trastuzumab, trastuzumab-emtansine (T-DM1) and tyrosine kinase inhibitors (TKIs). The combination of Amc and anti-HER2 therapies was investigated in a panel of four HER2+/ER+ cell lines: BT-474, MDA-MB-361, EFM-192a and a trastuzumab-resistant variant BT-474-T. Proliferation (IC50 and matrix combination assays) was determined using acid phosphatase assays. HER2/ER and intracellular signalling pathway protein levels/activity were investigated by western blot. Apoptosis was assessed using caspase 3/7 assays. Additivity and synergy were observed between Amc and the TKIs neratinib, lapatinib and tucatinib in all cell lines. Amc increased the anti-proliferative effect of trastuzumab in MDA-MB-361 and BT-474-T. Addition of Amc also increased anti-proliferative efficacy of T-DM1 in BT-474-T. TKI/Amc combinations reduced p-HER2 and ER levels and resulted in increased apoptosis. Higher ER expression in MDA-MB-361 and BT-474-T was associated with greater potential for synergy. In conclusion, the combination of Amc- and HER2-targeted treatments has potential as a therapeutic strategy for the treatment of HER2+/ER+ breast cancer and warrants further clinical investigation to validate safety and efficacy in patients.

Enhancing the Safety and Efficacy of Trastuzumab Emtansine (T-DM1) Through Nano-Delivery System in Breast Cancer Therapy.

Trastuzumab emtansine (T-DM1), an antibody-drug conjugate, revolutionizes breast cancer therapy by specifically delivering DM1 to human epidermal growth factor receptor 2 (HER2) overexpressing tumor cells, effectively inhibiting cell division and proliferation. While T-DM1 demonstrates superior efficacy and tolerability, T-DM1-induced thrombocytopenia remains a significant adverse event leading to treatment discontinuation. To address this issue, the study investigates the feasibility of using poly(lactic-co-glycolic acid) (PLGA)nanoparticles as a delivery vehicle to conjugate T-DM1, aiming to alleviate T-DM1-induced thrombocytopenia. The T-DM1-conjugated PLGA nanoparticles (NPs-T-DM1) reduce binding to megakaryocytes without compromising the targeting ability for HER2. Administration of NPs-T-DM1 not only significantly inhibits tumor growth but also reduces damage to megakaryocytes, inhibits T-DM1-induced thrombocytopenia, and remarkably improves the safety of antibody-conjugated drugs. This work presents a promising strategy to enhance the safety and efficacy of T-DM1 in antitumor therapy, offering significant potential for advancing clinical application in HER2-positive breast cancer patients.

Neratinib and ado-trastuzumab emtansine for pretreated and untreated human epidermal growth factor receptor 2 (HER2)-positive breast cancer brain metastases: Translational Breast Cancer Research Consortium trial 022

Treatment options for human epidermal growth factor receptor 2 (HER2)-positive breast cancer brain metastases (BCBMs) remain limited. We previously reported central nervous system (CNS) activity for neratinib and neratinib-capecitabine. Preclinical data suggest that neratinib may overcome resistance to ado-trastuzumab emtansine (T-DM1) when given in combination. In Translational Breast Cancer Research Consortium (TBCRC) 022's cohort 4, we examined the efficacy of neratinib plus T-DM1 in patients with HER2-positive BCBM. In this multicenter, phase II study, patients with measurable HER2-positive BCBM received neratinib 160 mg daily plus T-DM1 3.6 mg/kg intravenously every 21 days in three parallel-enrolling cohorts [cohort 4A-previously untreated BCBM, cohorts 4B and 4C-BCBM progressing after local CNS-directed therapy without (4B) and with (4C) prior exposure to T-DM1]. Cycle 1 diarrheal prophylaxis was required. The primary endpoint was the Response Assessment in Neuro-Oncology-Brain Metastases (RANO-BM) by cohort. The overall survival (OS) and toxicity were also assessed. Between 2018 and 2021, 6, 17, and 21 patients enrolled in cohorts 4A, 4B, and 4C. Enrollment was stopped prematurely for slow accrual. The CNS objective response rate in cohorts 4A, 4B, and 4C was 33.3% [95% confidence interval (CI) 4.3% to 77.7%], 35.3% (95% CI 14.2% to 61.7%), and 28.6% (95% CI 11.3% to 52.2%), respectively; 38.1%-50% experienced stable disease for ≥6 months or response. Diarrhea was the most common grade 3 toxicity (22.7%). The median OS was 30.2 [cohort 4A; 95% CI 21.9-not reached (NR)], 23.3 (cohort 4B; 95% CI 17.6-NR), and 20.9 (cohort 4C; 95% CI 14.9-NR) months. We observed intracranial activity for neratinib plus T-DM1, including those with prior T-DM1 exposure, suggesting synergistic effects with neratinib. Our data provide additional evidence for neratinib-based combinations in patients with HER2-positive BCBM, even those who are heavily pretreated.

Prognostic Significance of Pan-Immune-Inflammation Value in Patients with HER2-Positive Metastatic Breast Cancer Treated with Trastuzumab Emtansine.

Trastuzumab emtansine (T-DM1) is a mainstay therapy for HER2-positive metastatic breast cancer (mBC). However, identifying patients who will benefit most remains a challenge due to the lack of reliable biomarkers. The recently developed pan-immune-inflammation value (PIV), a novel immune-inflammation marker, could aid in this regard, considering the immunomodulatory effects of T-DM1. Therefore, we aimed to evaluate the association between the PIV and the efficacy of T-DM1 in patients with HER2-positive mBC. A total of 122 HER2-positive mBC patients treated with T-DM1 were included. Receiver operating characteristic (ROC) curve analyses were conducted to determine the optimal PIV threshold value for survival prediction. Kaplan-Meier survival curves and Cox regression analyses were used for univariable and multivariable survival analyses, respectively. The median age was 51 years, and 95.1% of the patients had ECOG PS 0-1. The optimal PIV cutoff value was identified as 338 in ROC analyses (AUC: 0.667, 95% CI: 0.569-0.765, p = 0.002). The multivariate analysis revealed that patients in the high-PIV group had significantly shorter OS (HR: 2.332; 95% CI: 1.408-3.861; p = 0.001) and PFS (HR: 2.423; 95% CI: 1.585-3.702; p < 0.001) than patients in the low-PIV group. Additionally, both ORR and DCR were significantly lower in the high-PIV group (36.6% vs. 61.3%, p = 0.011; 56.1% vs. 76.0%, p = 0.027). Our findings suggest that pre-treatment PIV may be a novel prognostic biomarker for HER2-positive mBC patients receiving T-DM1. A low PIV level is associated with more favorable outcomes. Future prospective studies are warranted to validate these findings and explore the potential utility of PIV in aiding treatment decisions.

Combining Endocrine Therapy with Trastuzumab Emtansine Improves Progression-Free Survival and Overall Survival in HER2-Positive, Hormone Receptor-Positive Metastatic Breast Cancer.

Background and Objectives: Patients with human epidermal growth factor receptor 2 (HER2) -positive, hormone receptor-positive (HR-positive) metastatic breast cancer (MBC) usually undergo trastuzumab emtansine (T-DM1) therapy in subsequent lines. Combining endocrine therapy (ET) with T-DM1 can improve treatment outcomes in this subtype. Therefore, this study aimed to investigate the benefits of using T-DM1 with ET in HER2-positive and HR-positive MBC. This study was the first to investigate the benefits of combining ET with T-DM1. Material and Methods: This study analyzed the medical records of patients with HER2-positive and HR-positive MBC who were treated with T-DM1 from June 2010 to December 2021. The patients were divided into groups based on whether they received concomitant ET with T-DM1. The primary endpoint was to determine the progression-free survival (PFS), while the secondary endpoints were overall survival (OS), objective response rate, and safety of the treatment. Results: Our analysis examined 88 patients, of whom 32 (36.4%) were treated with T-DM1 in combination with ET. The combination therapy showed a significant improvement in median PFS (15.4 vs. 6.4 months; p = 0.00004) and median OS (35.0 vs. 23.1 months; p = 0.026) compared to T-DM1 alone. The ORR was also higher in the combination group (65.6% vs. 29.3%; p = 0.026). Patients treated with pertuzumab priorly had reduced median PFS on T-DM1 compared to those who were not treated with pertuzumab (11.7 vs. 5.4 months, respectively; p < 0.01). T-DM1 demonstrated better median PFS in HER2 3+ patients compared to HER2 2+ patients, with an amplification ratio of >2.0 (10.8 vs 5.8 months, respectively; p = 0.049). The safety profiles were consistent with previous T-DM1 studies. Conclusions: The combination of T-DM1 with ET can significantly improve PFS and OS in patients with HER2-positive and HR-positive MBC. Our study suggests that prior pertuzumab treatment plus trastuzumab treatment might decrease T-DM1 efficacy.

Safety and efficacy of biosimilar TDM-1: A real world retrospective study.

3022 Background: Ado-Trastuzumab emtansine (TDM1), an antibody-drug conjugate demonstrated significant efficacy in both metastatic and adjuvant treatment of HER 2 Positive Breast cancer. Cost of the drug was prohibitive for use in Low and Middle income countries (LMIC). A biosimilar version of TDM1 was introduced in India at a lower price in May 2021. Since then, the use of TDM1 in deserving patients has increased. We aimed to study the safety and efficacy of biosimilar TDM1 in our center. Methods: We retrospectively analysed the case records of all patients who were prescribed biosimilar TDM1 at our institute from 01.06.2021 to 20.10.2023. Indication for TDM1, line of therapy in which used, number of cycles used, response rates, adverse events, progression free survival and overall survival were calculated using simple statistical methods. The usage of any TDM1 after May 2021 was compared to the previous years’ usage. Results: A total of 116 patients were prescribed biosimilar TDM1 in the study period. Out of them, 51 patients received the drug in the adjuvant setting and 65 for advanced stage disease. Early stage (n=51): Out of the 51 patients, 32 (62.7%) completed planned cycles, 14 (27.5%) ongoing; 3 (5.9%) discontinued due to social reasons, 2 (3.9%) changed treatment due to adverse events. All of them tolerated the therapy well. Common adverse effects were fatigue. Only 5 patients (21.7%) required romiplostim for therapy related thrombocytopenia. None of them had grade ≥3 adverse affects. Advanced stage (n=65): At a median follow up of 9 months, 30 patients (46.2%) progressed; 15 (23%) ongoing; 15 (23%) defaulted due to various social reasons; 5 (7.7%) discontinued due to intolerance. The median number of cycles received was 8 cycles (IQR 5-13). Majority of them received TDM1 in the second line (84.6%). Response evaluation was available for 52 patients who completed at least three cycles of TDM1. Objective response rate was noted in 33 patients (50.8%). Clinical benefit rate (CR+PR+SD) was seen in 39 patients (75%). 5 patients (9.6%) had a Complete response, 28 (53.8%) had Partial response and 6 (11.5%) had a stable disease. The median duration of response was 5 months. The median Progression Free survival was 8 months (5.7– 10.2m) and the projected overall survival was 18 months (16.1-19.9 m). No serious adverse event or cardiac compromise was encountered. 3 patients had thrombocytopenia. One patient succumbed to non-neutropenic Septic shock. In a retrospective data analysis, TDM1 was used in 17 patients in one calendar year prior to the availability of generic TDM1. In the subsequent year, 60 patients received TDM1 at least once in either indication. Conclusions: The availability of biosimilar TDM1 increased the reach to deserving patients. No new adverse events were identified. The safety and efficacy of the biosimilar TDM1 were comparable.

Trastuzumab deruxtecan (T-DXd) vs trastuzumab emtansine (T-DM1) in patients (pts) with HER2+ metastatic breast cancer (mBC): Updated survival results of DESTINY-Breast03.

1025 Background: DESTINY-Breast03 (NCT03529110), a randomized, multicenter, open-label, phase 3 study, assessed the efficacy and safety of T-DXd vs T-DM1 in pts with HER2+ mBC treated with ≥1 prior anti-HER2 regimen. Median (m) overall survival (OS) was not reached in either arm at the prior data cutoff (DCO; Jul 25, 2022). We report updated survival results, including efficacy and safety, after median duration of follow-up of 41 mo. Methods: Pts were randomized 1:1 to T-DXd 5.4 mg/kg or T-DM1 3.6 mg/kg once every 3 weeks. Primary endpoint was progression-free survival (PFS) by blinded independent central review (assessed at prior DCO); key secondary endpoint was OS. Other secondary endpoints included objective response rate (ORR), PFS, duration of response (DoR), PFS from time of randomization to progression on next line of therapy or death (PFS2), and safety. All secondary endpoints were based on investigator assessment. Results: 524 pts were randomized (T-DXd, n = 261; T-DM1, n = 263). As of Nov 20, 2023, median duration of follow-up was 43.0 mo (range, 0.0-62.9) for T-DXd and 35.4 mo (range, 0.0-60.9) for T-DM1. mOS (95% CI) was 52.6 mo (48.7-not evaluable [NE]) for T-DXd and 42.7 mo (35.4-NE) for T-DM1 (hazard ratio [HR], 0.73), with 110 (42.1%) and 126 (47.9%) OS events, respectively. OS rate (95% CI) at 36 mo was 67.6% (61.3-73.0%; T-DXd) vs 55.7% (49.2-61.7%; T-DM1). mPFS was 29.0 mo for T-DXd and 7.2 mo for T-DM1; PFS rate (95% CI) at 24 mo was 55.8% (49.1-62.0%; T-DXd) vs 20.6% (15.4-26.4%; T-DM1). mPFS2 was 45.2 mo (T-DXd) vs 23.1 mo (T-DM1). Median treatment duration was 18.2 mo (range, 0.7-56.6) with T-DXd vs 6.9 mo (range, 0.7-55.2) with T-DM1; rates of treatment-emergent adverse events (TEAEs) were consistent with prior DCO. Adjudicated drug-related interstitial lung disease/pneumonitis occurred in 16.7% of pts with T-DXd (4 new events [all grade 2] since prior DCO) vs 3.4% with T-DM1 (1 new event [grade 1]); neither arm had grade 4 or 5 events. Key efficacy and safety results are shown in the table. Conclusions: The superiority of T-DXd over T-DM1 was reinforced in this long-term analysis, as observed by clinically meaningful improvement in OS, PFS, and PFS2, consistent with prior DCO. The safety profile of T-DXd continues to be manageable with no cumulative toxicities observed with longer follow-up. Clinical trial information: NCT03529110 . [Table: see text]

NSABP FB-10: a phase Ib/II trial evaluating ado-trastuzumab emtansine (T-DM1) with neratinib in women with metastatic HER2-positive breast cancer

BackgroundWe previously reported our phase Ib trial, testing the safety, tolerability, and efficacy of T-DM1 + neratinib in HER2-positive metastatic breast cancer patients. Patients with ERBB2 amplification in ctDNA had deeper and more durable responses. This study extends these observations with in-depth analysis of molecular markers and mechanisms of resistance in additional patients.MethodsForty-nine HER2-positive patients (determined locally) who progressed on-treatment with trastuzumab + pertuzumab were enrolled in this phase Ib/II study. Mutations and HER2 amplifications were assessed in ctDNA before (C1D1) and on-treatment (C2D1) with the Guardant360 assay. Archived tissue (TP0) and study entry biopsies (TP1) were assayed for whole transcriptome, HER2 copy number, and mutations, with Ampli-Seq, and centrally for HER2 with CLIA assays. Patient responses were assessed with RECIST v1.1, and Molecular Response with the Guardant360 Response algorithm.ResultsThe ORR in phase II was 7/22 (32%), which included all patients who had at least one dose of study therapy. In phase I, the ORR was 12/19 (63%), which included only patients who were considered evaluable, having received their first scan at 6 weeks. Central confirmation of HER2-positivity was found in 83% (30/36) of the TP0 samples. HER2-amplified ctDNA was found at C1D1 in 48% (20/42) of samples. Patients with ctHER2-amp versus non-amplified HER2 ctDNA determined in C1D1 ctDNA had a longer median progression-free survival (PFS): 480 days versus 60 days (P = 0.015). Molecular Response scores were significantly associated with both PFS (HR 0.28, 95% CI 0.09–0.90, P = 0.033) and best response (P = 0.037). All five of the patients with ctHER2-amp at C1D1 who had undetectable ctDNA after study therapy had an objective response. Patients whose ctHER2-amp decreased on-treatment had better outcomes than patients whose ctHER2-amp remained unchanged. HER2 RNA levels show a correlation to HER2 CLIA IHC status and were significantly higher in patients with clinically documented responses compared to patients with progressive disease (P = 0.03).ConclusionsThe following biomarkers were associated with better outcomes for patients treated with T-DM1 + neratinib: (1) ctHER2-amp (C1D1) or in TP1; (2) Molecular Response scores; (3) loss of detectable ctDNA; (4) RNA levels of HER2; and (5) on-treatment loss of detectable ctHER2-amp. HER2 transcriptional and IHC/FISH status identify HER2-low cases (IHC 1+ or IHC 2+ and FISH negative) in these heavily anti-HER2 treated patients. Due to the small number of patients and samples in this study, the associations we have shown are for hypothesis generation only and remain to be validated in future studies.Clinical Trials registration NCT02236000

Targeting TACC3 Induces Immunogenic Cell Death and Enhances T-DM1 Response in HER2-Positive Breast Cancer.

Loss of induction of immunogenic cell death in response to T-DM1 leads to resistance that can be overcome by targeting TACC3, providing an attractive strategy to improve the efficacy of T-DM1.

Meta-analysis of the clinical efficacy and safety of T-DM1 in the treatment of HER2-positive breast cancer.

This meta-analysis aims to comprehensively evaluate the efficacy and safety of T-DM1 in treating HER2-positive breast cancer, providing insights for clinical practice. We conducted a literature search in PubMed, Cochrane Library, and Embase databases up to September 2023, collecting randomized controlled trials and cohort studies on T-DM1 for HER2-positive breast cancer. Out of 316 initially retrieved articles, 12 studies meeting the quality and inclusion criteria were included after a rigorous screening process. We used RevMan 5.3 software for the meta-analysis, employing fixed or random-effect models. Odds ratios (RRs) and 95% confidence intervals (CIs) were calculated as effect size measures. We conducted sensitivity analyses and assessed publication bias to ensure the results' stability and reliability. In seven studies, T-DM1 treatment significantly prolonged OS in patients with HER2-positive breast cancer [hazard ratio (HR) = 0.70, 95% CI: 0.64-0.77, P < 0.01], and the effect was especially pronounced in patients with advanced disease (HR = 0.64, 95% CI: 0.54-0.76, P < 0.001). Analysis of pCR rates did not show a significant difference (OR = 0.91, 95% CI: 0.48-1.73, P = 0.77). In five studies, ORR improved, but the difference between the two groups was not significant (OR = 1.16, 95% CI: 0.66-2.05, P = 0.61). Analysis of progression-free survival (PFS) showed a significant improvement in the experimental group relative to the control group (HR = 0.69, 95% CI: 0.57-0.84, P = 0.0003). Regarding the incidence of total adverse events, no significant difference was seen between the two groups (OR = 2.16, 95% CI: 0.98-4.79, P = 0.06), but for specific adverse events, such as leukopenia and neutropenia, the T-DM1 group demonstrated a significant reduction relative to the other treatment regimens. The results underscore the potential of T-DM1 in enhancing survival among patients with advanced HER2-positive breast cancer, yet they also highlight variability in effectiveness concerning pCR rate and ORR. The findings on adverse effects underscore the necessity of a balanced consideration of T-DM1's risks and benefits. Future research should focus on a more detailed examination of responses in varied patient populations, long-term outcomes, and a thorough economic evaluation of T-DM1, along with an exploration into treatment resistance. This will provide a more nuanced understanding of T-DM1's role in the treatment landscape of HER2-positive breast cancer.

Macrolide and Ketolide Antibiotics Inhibit the Cytotoxic Effect of Trastuzumab Emtansine in HER2-Positive Breast Cancer Cells: Implication of a Potential Drug-ADC Interaction in Cancer Chemotherapy.

Macrolides are widely used for the long-term treatment of infections and chronic inflammatory diseases. The pharmacokinetic features of macrolides include extensive tissue distribution because of favorable membrane permeability and accumulation within lysosomes. Trastuzumab emtansine (T-DM1), a HER2-targeting antibody-drug conjugate (ADC), is catabolized in the lysosomes, where Lys-SMCC-DM1, a potent cytotoxic agent, is processed by proteinase degradation and subsequently released from the lysosomes to the cytoplasm through the lysosomal membrane transporter SLC46A3, resulting in an antitumor effect. We recently demonstrated that erythromycin and clarithromycin inhibit SLC46A3 and attenuate the cytotoxicity of T-DM1; however, the effect of other macrolides and ketolides has not been determined. In this study, we evaluated the effect of macrolide and ketolide antibiotics on T-DM1 cytotoxicity in a human breast cancer cell line, KPL-4. Macrolides used in the clinic, such as roxithromycin, azithromycin, and josamycin, as well as solithromycin, a ketolide under clinical development, significantly attenuated T-DM1 cytotoxicity in addition to erythromycin and clarithromycin. Of these, azithromycin was the most potent inhibitor of T-DM1 efficacy. These antibiotics significantly inhibited the transport function of SLC46A3 in a concentration-dependent manner. Moreover, these compounds extensively accumulated in the lysosomes at the levels estimated to be 0.41-13.6 mM when cells were incubated with them at a 2 μM concentration. The immunofluorescence staining of trastuzumab revealed that azithromycin and solithromycin inhibit the degradation of T-DM1 in the lysosomes. These results suggest that the attenuation of T-DM1 cytotoxicity by macrolide and ketolide antibiotics involves their lysosomal accumulation and results in their greater lysosomal concentrations to inhibit the SLC46A3 function and T-DM1 degradation. This suggests a potential drug-ADC interaction during cancer chemotherapy.

Real-world outcomes of long-term efficacy of T-DM1 after discontinuation due to limiting toxicity in patients with HER2-positive metastatic breast cancer.

e13034 Background: Antibody-drug conjugates (ADC) are widely used in the treatment of breast cancer (BC). In our service, we observed that a significant number of patients (pts) with HER2-positive metastatic breast cancer (MBC) treated with T-DM1 had long-lasting response and survival rates, even after discontinuing T-DM1 due to limiting toxicity. However, data are scarce regarding its long-term benefit. We performed a retrospective study to evaluate the long-term efficacy of T-DM1 in the treatment of HER2-positive MBC. Methods: Medical records of pts with HER2-positive MBC treated with T-DM1 between September 2013 and January 2023 were reviewed. We analyzed data in the overall population and in the subgroup of pts who discontinued T-DM1 due to only limiting toxicity and did not have disease progression or death for at least 12 months, without receiving other subsequent lines of treatment. The primary endpoints were progression-free survival (PFS) and overall survival (OS) from the start of the treatment with T-DM1 to disease progression or death for the overall population, and from the time of T-DM1 discontinuation to disease progression or death for the aforementioned subgroup. Secondary endpoints were objective response rate (ORR) and toxicity. Results: A total of 73 pts were included. In the overall population, ORR was 82.6%, median PFS was 12.7 months (CI95% 8-16) and median OS was 53.9 months (CI95% 34-73). 10 (13.6%) pts had T-DM1 discontinued due to only limiting toxicity and had no disease progression or death for at least 12 months. In this specific subgroup, 2 pts received T-DM1 as first line, 6 pts as second line, and 2 as third or more lines. At the start of T-DM1, 5 pts had visceral metastasis (3 liver, 2 lung), and 2 had only leptomeningeal involvement. Median age was 57 years (IQR 49-70) and median T-DM1 duration was 30 months (IQR 12-45). At the time of T-DM1 discontinuation, 9 pts presented complete response (CR) and 1 presented partial response (PR). 5 pts maintained CR, with no evidence of disease progression or death throughout the analyzed period. The PFS of these 5 pts, from the time of T-DM1 discontinuation to the last evaluation, was 35.6, 37.9, 40.5, 42.7 and 68.5 months. In the entire subgroup, median PFS was 22.5 months, 5-year OS was 66.7% and median OS was not reached. The adverse events that led to the T-DM1 discontinuation were thrombocytopenia (10%), nausea, vomiting and fatigue (10%), pneumonitis (20%), hepatic pseudocirrhosis (20%) and peripheral neuropathy (40%). Conclusions: Our experience suggests that pts with HER2-positive MBC who had T-DM1 discontinued due to limiting toxicity may derive long-term benefit. Further prospective studies are warranted to evaluate our findings, also including other ADC.

Abstract P5-02-21: RAB5 is a generic biomarker for ADC efficacy

Abstract Antibody-drug conjugates (ADCs) have demonstrated impressive activity in recent clinical trials in breast cancer. Such targeted therapeutics strongly depends on the presence of target molecules on the tumor cells, and the presence of such target molecules may determine the response of ADCs. However, ADCs are also dependent on cellular uptake, and factors regulating endocytosis as well as intracellular trafficking may strongly influence ADC activity. We have recently demonstrated that the activity of the HER2 targeted ADC trastuzumab emtansine (T-DM1) is dependent on the expression of RAB5A, a protein regulating endocytosis (1). A significant correlation between Rab5A expression and T-DM1 efficacy was found in a panel of HER2 expressing breast- and ovarian cancer cell lines. This result was verified in the I-SPY2 clinical trial where patients with high RAB5A expression were more likely to achieve a pathological complete response following T-DM1 as a neoadjuvant. The result was further validated in patients treated with T-DM1 in the Kamilla study where patients with a high RAB5A had a longer progression free survival. All ADCs should in principle be dependent on endocytosis to exert their activity. This triggered the investigation of proteins regulating endocytosis as predictive biomarkers for ADCs in general. METHODS: HER2-positive breast and ovarian cancer cell lines were evaluated with respect to the sensitivity and efficacy of treatment with T-DM1, trastuzumab deruxtecan, sacituzumab govitecan and the targeted toxin MH3B1/rGel.. The expression levels of proteins involved in endocytosis and endocytic trafficking including RAB4A, RAB5A and RAB11A were investigated in addition to the molecular drug targets (HER2 and TROP2). Cellular drug sensitivity was correlated to the expression levels of the investigated proteins using both RNA and protein as readout. RESULTS: The early endosome marker RAB5A, was found to correlate positively to the activity of trastuzumab deruxtecan, sacituzumab govitecan and MH3B1/rGel in the HER2 positive cell line panel, confirming the importance of RAB5A expression for the activity of these drugs. A significant correlation was found between RAB5A and drug efficacy using both protein and RNA as a readout. CONCLUSION: The present results indicate RAB5A as a generic predictive biomarker for both ADCs and targeted toxins which both depend on cellular uptake for cytotoxic efficacy. The results supports using both protein and RNA as a readout for RAB5A expression and point towards the development of a RAB5A stratification procedure for ADC and targeted toxin treatment. 1. Engebraaten O, Yau C, Berg K, Borgen E, Garred O, Berstad MEB, Fremstedal ASV, DeMichele A, Veer LV, Esserman L, Weyergang A. RAB5A expression is a predictive biomarker for trastuzumab emtansine in breast cancer. Nature communications 2021;12(1):6427 doi 10.1038/s41467-021-26018-z. Citation Format: Olav Engebraaten, Astrid Medhus, Ane Longva, Anette Weyergang, Kristian Berg. RAB5 is a generic biomarker for ADC efficacy [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 P5-02-21.

Effectiveness and cost-effectiveness of trastuzumab emtansine in women with HER2-positive locally advanced or metastatic breast cancer: A systematic review and meta-analysis.

Trastuzumab emtansine (T-DM1) is a human epidermal growth factor receptor-2 targeted antibody-drug conjugate that contains a monoclonal antibody, trastuzumab, covalently linked to DM1, a small molecule cytotoxin. We conducted a systematic review and meta-analysis of published trials to examine the efficacy and safety of T-DM1 for patients with HER2-positive metastatic breast cancer. In addition, we systematically reviewed existing economic evaluations of T-DM1. An electronic literature search of online databases (Medline, CENTRAL, and Embase) was performed. Randomized controlled trials that compared T-DM1 with other active treatment agents were eligible for inclusion. In addition, studies that involved T-DM1 as one of the treatment comparators in an economic evaluation were included. Four trials with a total of 2462 participants were included in this meta-analysis. Pooled results showed T-DM1 substantially improved overall survival (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.67-0.85; I2 = 0%) and progression-free survival (HR, 0.67; 95% CI, 0.52-0.85; I2 = 75%). In addition, T-DM1 showed greater association with severe thrombocytopenia and liver dysfunction than other regimens, but a lower rate of neutropenia, leukopenia, febrile neutropenia, asthenia, and diarrhea. All four trials included in the meta-analysis overall had a low risk of bias. Two cost-utility analyses involving T-DM1 were identified, and the overall quality was high. T-DM1 is effective for the treatment of patients with HER2-positive metastatic breast cancer, and it demonstrates a tolerable safety profile compared with other active controls. Little evidence was available regarding the cost-effectiveness of T-DM1 so no conclusions can be drawn.

Combination of T-DM1 and platinum-based chemotherapy in patient-derived xenograft models of muscle-invasive bladder cancer.

Objective(s):To assess the efficacy and safety of T-DM1, as an anti-HER2 antibody-drug conjugate (ADC), alone and in combination with two platinum-based chemotherapy regimens in patient-derived xenografts (PDXs) of muscle-invasive bladder cancer (MIBC) established in immunodeficient mice. Materials and Methods:After treatment initiation, tumor size was measured twice a week. Percent of tumor growth inhibition (TGI) and tumor response rates were calculated as efficacy endpoints. To evaluate treatment toxicity, relative body weight (RBW) was calculated for each group. For comparison of TGIs between treatment groups, the Kruskal-Wallis test was used. Also, the significance of the overall response (OR) rate between placebo groups with treatment groups was analyzed using Fisher’s exact test. Immunohistochemistry and fluorescence in situ hybridization techniques were used to evaluate the level of HER2 expression.Results:Our data showed that T-DM1 alone induced a moderate antitumor activity. While chemotherapy regimens induced a slight TGI when administered alone, interestingly, they showed strong antitumor activity when administered combined with T-DM1. The OR rates were higher when T-DM1 was combined with chemotherapy regimens than T-DM1 alone. When compared with the placebo group, the OR rates of combination groups were statistically significant. Our data also showed that the administered dose of each drug was well tolerated in mice. Conclusion:The combination of T-DM1 and platinum-based chemotherapy may represent a new treatment option for bladder tumors with even low HER2 expression, and could also provide substantial novel insight into tackling the challenges of MIBC management.

Abstract 1787: Statin therapy enhances the efficacy of HER2 directed antibody-drug conjugates in breast cancer

Abstract Antibody-drug conjugates (ADCs) targeting human epidermal growth factor receptor 2 (HER2) are a widely successful strategy for the treatment of HER2-positive breast cancer. Despite the demonstrated efficacy, intrinsic and acquired resistance to anti-HER2 ADCs remains a major challenge. The activity of ADCs is dependent upon the internalization of the HER2-ADC complex into specific subcellular compartments permissive for release of the chemotherapeutic payload. Previous studies have demonstrated that statins, a commonly used cholesterol-lowering medication, could increase plasma membrane-bound HER2 and improve trastuzumab efficacy in HER2-positive gastric cancer. In this study, we sought to characterize the impact of statins on the efficacy of HER2 ADCs. We performed in vitro internalization assays with trastuzumab emtansine (T-DM1) labeled with a pH-sensitive pHrodo fluorogenic dye to monitor T-DM1 entering lysosome whereupon payload DM1 is released, and found that combined treatment of T-DM1 and lovastatin potently enhanced T-DM1 internalization of T-DM1 into lysosome in HER2-amplified and HER2-low models. Consistent with the internalization assays, lovastatin increased cell death caused by T-DM1 and sensitized the HER2-low ZR75-1 cells to T-DM1 treatment in vitro. Using HER2-positive xenograft models, we found orally administrated lovastatin promoted T-DM1 uptake in tumors and enhanced T-DM1 efficacy in vivo. To investigate whether these results might be observed in the clinic, we conducted retrospective analyses on a cohort of 164 HER2 positive metastatic breast cancer patients treated at MSKCC who received T-DM1. Among these patients, 21 (12.8%) were taking statins concurrently with T-DM1, and the median progression-free survival in the patients who received statins was 14 months (95% confidence interval, 3.5-24 months) compared to 5.4 months (95% confidence interval, 3.9-7.0 months) in those who had no record of statin use (p=0.1). Overall, our findings demonstrate that statins potentiate the susceptibility of breast cancer cells to anti-HER2 ADCs by modulating HER2 membrane dynamics and HER2-ADC internalization, suggesting statin as a rational therapeutic partner for anti-HER2 ADC in HER2-positive breast cancer, especially those with relatively low HER2 expression. Citation Format: Bo Liu, Joshua Z. Drago, Yi Rao, Patricia R. Pereira, Anton Safonov, Antonio Marra, Mehnaj S. Ahmed, Shanu Modi, Jorge S. Reis-Filho, Filippo Montemurro, Pedram Razavi, Jason S. Lewis, Sarat Chandarlapaty. Statin therapy enhances the efficacy of HER2 directed antibody-drug conjugates in breast cancer [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 1787.

T-DM1 efficacy in trastuzumab-pertuzumab pre-treated HER2 positive metastatic breast cancer patients: a meta-analysis

BackgroundCurrent guidelines consider T-DM1 the standard 2nd line therapy for HER2 positive metastatic breast cancer (MBC) patients following trastuzumab (T) + pertuzumab (P) and taxane 1st line treatment. Despite this, there are no prospective studies supporting this sequence.MethodsWe performed a meta-analysis using real world data to determine the efficacy of T-DM1 after 1st line TP in HER2 positive MBC patients. We used a random-effect model to find differences in the rate of 1-year progression free survival (PFS) between TP pre-treated population and the EMILIA phase III pivotal trial.ResultsSeven studies were eligible. The meta-analysis showed a combined 1-year PFS risk difference for T-DM1 efficacy after TP in 2nd or more lines of -0.122, with lower and upper limits of -0.253 and 0.010, respectively (p = 0.07), with low heterogeneity among studies (I2 0.01%, p = 0.836). Considering the four studies on T-DM1 in 2nd line setting, 1-year PFS risk was -0.034 (95% CI -0.207 – 0,139; p = 0.701) (I2 0.01%, p = 0.91).ConclusionOverall, the efficacy of T-DM1 after TP seems to be similar to that previously reported in the EMILIA trial. In the second line setting, data are not mature enough to confirm T-DM1 efficacy in TP pre-treated population.

Safety, efficacy and survival outcome of Ado-trastuzumab emtansine (T-DM1) in patients with metastatic HER2-positive breast cancer: An Indian experience.

e13008 Background: Ado-trastuzumab emtansine (T-DM1) is the standard of care for patients with advanced HER2 positive breast cancer (BC) patients who progress on the first line anti-HER2 therapy or relapse within 6 months of adjuvant trastuzumab. There is a lack of data regarding the safety and efficacy of T-DM1 in the Indian population. Methods: This retrospective study aims to evaluate the efficacy and toxicity of T-DM1 in advanced HER2 positive female BC patients, registered at All India Institute of Medical Sciences, (AIIMS) New Delhi, India, between the years 2015-2021. The response was evaluated by Response evaluated Criteria in Solid Tumors(RECIST 1.1)guidelines. Progression-free survival (PFS) was calculated from the beginning of treatment with T-DM1 until disease progression or death from any cause. Overall survival (OS) was calculated from the beginning of treatment with T-DM1 until death from any cause. Results: This study included eighty patients with a median age of 49 years (27-73). Forty-four (55%) were premenopausal and hormone receptor positivity (either ER or PR) was found in 36 (45%) cases. The ECOG performance status was 0-1in 80% of patients. De- novo metastatic disease was found in 38(47.5%) cases whereas the remaining 42 (52.5%) patients were diagnosed with early or locally advanced disease and later become metastatic. The sites of metastasis were lungs in 26 (32.5%), brain in 23 (28.7%) liver in 23 (28.7%), bones in 18 patients (22.5%), lymph nodes in 15(18.7%), cutaneous and other rare sites in 8(10%) cases. All patients had received trastuzumab in the prior line of treatment and 18 (22.5%) patients had also received pertuzumab along with trastuzumab. The median number of T-DM1 cycles given was 9 (range 3-35). The overall response rate was 80%, 8(10%) achieved a complete response, 36 (45%) had a partial response, and 12 (15%) patients had stable disease. The Grade 3/4 toxicities were observed in 20(25%) cases and these were: thrombocytopenia 16 (20%), fatigue 10 (12.5%), transaminitis 10(12.5%), anemia 2 (2.5%), and peripheral neuropathy in 2 (2.5%) cases. Dose delay, interruption, and modification were observed in 25 (31.2%) cases. Within the median follow-up period of 18 months, the median PFS was 10 months and OS was 27 months. Hormone status (ER/PR) and prior pertuzumab therapy did not influence the outcome. Conclusions: This is the first study from the Indian subcontinent on T-DM1. It is safe and effective in our population and has shown comparable outcomes with the available literature however, higher rates of thrombocytopenia were observed.

MTOR Inhibition and T-DM1 in HER2-Positive Breast Cancer.

Inhibition of mTOR increases the antitumor activity of T-DM1, supporting that the combination of mTOR inhibitors and antibody-drug conjugates warrants clinical evaluation in patients with HER2-positive breast cancer.