T-DM1 and brain metastases: Clinical outcome in HER2-positive metastatic breast cancer

Risk of radionecrosis in HER2-positive breast cancer with brain metastasis receiving trastuzumab emtansine (T-DM1) and brain stereotactic radiosurgery

OBJECTIVES

To investigate the potential relationship between trastuzumab emtansine (T-DM1) treatment and radionecrosis induced by brain stereotactic radiosurgery (SRS) in patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer.

MATERIALS AND METHODS

Patients with HER2-positive breast cancer who were diagnosed with brain metastasis and received both SRS and HER2-targeted agents between 2012 and 2022 were retrospectively analyzed. Patients who received T-DM1 within 1 year (either before or after) of SRS were considered as 'T-DM1 exposure (+)'. T-DM1 exposure (-) group had other HER2-targeted agents or received T-DM1 more than 1 year before or after SRS. Symptomatic radionecrosis was defined as Common Terminology Criteria for Adverse Events grade 2 or greater.

RESULTS

A total of 103 patients with 535 treatment sessions were included from seven tertiary medical centers in Korea and Italy. The median follow-up duration was 15.5 months (range 1.1-101.9). By per-patient analysis, T-DM1 exposure (+) group had an increased risk of overall radionecrosis after multivariate analysis (HR 2.71, p = 0.020). Additionally, T-DM1 exposure (+) group was associated with a higher risk of symptomatic radionecrosis compared to T-DM1 exposure (-) patients (HR 4.34, p = 0.030). In per-treatment analysis, T-DM1 exposure (+) was linked to higher incidences of overall (HR 3.13, p = 0.036) and symptomatic radionecrosis (HR 10.4, p = 0.013) after multivariate analysis. A higher prevalence of radionecrosis was observed with T-DM1 exposure (+) and a previous history of whole brain radiotherapy.

CONCLUSION

An increased risk of radionecrosis was observed in patients receiving T-DM1 with brain SRS. Further research is needed to better understand the optimal sequence and interval for administering T-DM1 and SRS.

Neratinib and Ado-Trastuzumab-Emtansine for Pre-treated and Untreated HER2-positive Breast Cancer Brain Metastases: Translational Breast Cancer Research Consortium Trial 022

PURPOSE

Treatment options for HER2-positive breast cancer brain metastases (BCBM) 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 TBCRC 022's cohort 4, we examined the efficacy of neratinib plus T-DM1 in patients with HER2-positive BCBM.

PATIENTS AND METHODS

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. Overall survival (OS) and toxicity were also assessed.

RESULTS

Between 2018-2021, 6, 17, and 21 patients enrolled to 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]: 4.3-77.7%), 35.3% (95% CI: 14.2-61.7%), and 28.6% (95% CI: 11.3-52.2%), respectively; 38.1-50% experienced stable disease for ≥6 months or response. Diarrhea was the most common grade 3 toxicity (22.7%). Median OS was 30.2 months (cohort 4A; 95% CI: 21.9, not reached [NR]), 23.3 months (cohort 4B; 95% CI: 17.6, NR), and 20.9 months (cohort 4C; 95% CI: 14.9, NR).

CONCLUSION

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 pre-treated.

Standard-of-Care Treatment for HER2+ Metastatic Breast Cancer and Emerging Therapeutic Options

Prior to the advent of the HER2-targeted monoclonal antibody trastuzumab, HER2+ breast cancer (BC) was considered an aggressive disease with a poor prognosis. Over the past 25 years, innovations in molecular biology, pathology, and early therapeutics have transformed the treatment landscape. With the advent of multiple HER2-directed therapies, there have been immense improvements in oncological outcomes in both adjuvant and metastatic settings. Currently, 8 HER2-targeted therapies are approved by the Food and Drug Administration (FDA) for the treatment of early-stage and/or advanced/metastatic disease. Nonetheless, approximately 25% of patients develop recurrent disease or metastasis after HER2-targeted therapy and most patients with HER2+ metastatic breast cancer (MBC) die from their disease. Given the many mechanisms of resistance to HER2-directed therapy, there is a pressing need to further personalize care for patients with HER2+ MBC, by the identification of reliable predictive biomarkers, and the development of novel therapies and combination regimens to overcome therapeutic resistance. Of particular interest are established and novel antibody-drug conjugates, as well as other novel therapeutics and multifaceted approaches to harness the immune system (checkpoint inhibitors, bispecific antibodies, and vaccine therapy). Herein, we discuss standard-of-care treatment of HER2+ MBC, including the management of breast cancer brain metastases (BCBM). Furthermore, we highlight novel treatment approaches for HER2+ MBC, including endeavors to personalize therapy, and discuss ongoing controversies and challenges.

Long-term response to sequential anti-HER2 therapies including trastuzumab-deruxtecan in a patient with HER2-positive metastatic breast cancer with leptomeningeal metastases: a case report and review of the literature

The incidence of leptomeningeal metastases (LM) is increasing among breast cancer patients, but their prognosis remains dismal. Many therapeutic options are now available to treat HER2-positive (HER2+) metastatic breast cancer (MBC) involving the central nervous system (CNS). This case report illustrates a long-lasting response of more than 2 years in a patient with HER2+ MBC with LM after sequential administration of systemic and intrathecal (IT) anti-HER2 therapies and highlights that an appropriate treatment of HER2+ LM can result in durable survival.

Clinical features and outcomes of advanced HER2+ esophageal/GEJ cancer with brain metastasis

BACKGROUND

Brain metastasis (BRM) is uncommon in gastroesophageal cancer. As such, clinicopathologic and molecular determinants of BRM and impact on clinical outcome remain incompletely understood.

METHODS

We retrospectively analyzed clinicopathologic data from advanced esophageal/gastroesophageal junction (E/GEJ) patients at Johns Hopkins from 2003 to 2021. We investigated the association between several clinical and molecular features and the occurrence of BRM, with particular focus on human epidermal growth factor receptor 2 (HER2) overexpression. Survival outcomes and time to BRM onset were also evaluated.

RESULTS

We included 515 patients with advanced E/GEJ cancer. Tumors were 78.3% esophageal primary, 82.9% adenocarcinoma, 31.0% HER2 positive. Cumulative incidence of BRM in the overall cohort and within HER2+ subgroup was 13.8% and 24.3%, respectively. HER2 overexpression was associated with increased risk of BRM [odds ratio 2.45; 95% confidence interval (CI) 1.10-5.46]. On initial presentation with BRM, 50.7% had a solitary brain lesion and 11.3% were asymptomatic. HER2+ status was associated with longer median time to onset of BRM (14.0 versus 6.3 months, P < 0.01), improved median progression free survival on first-line systemic therapy (hazard ratio 0.35, 95% CI 0.16-0.80), and improved median overall survival (hazard ratio 0.20, 95% CI 0.08-0.54) in patients with BRM.

CONCLUSION

HER2 overexpression identifies a gastroesophageal cancer molecular subtype that is significantly associated with increased risk of BRM, though with later onset of BRM and improved survival likely reflecting the impact of central nervous system-penetrant HER2-directed therapy. The prevalence of asymptomatic and solitary brain lesions suggests that brain surveillance for HER2+ patients warrants prospective investigation.

Management of Brain Metastases: A Review of Novel Therapies

Brain metastases (BMs) represent the most common intracranial tumors in adults, and most commonly originate from lung, followed by breast, melanoma, kidney, and colorectal cancer. Management of BM is individualized based on the size and number of brain metastases, the extent of extracranial disease, the primary tumor subtype, neurological symptoms, and prior lines of therapy. Until recently, treatment strategies were limited to local therapies, like surgical resection and radiotherapy, the latter in the form of whole-brain radiotherapy or stereotactic radiosurgery. The next generation of local strategies includes laser interstitial thermal therapy, magnetic hyperthermic therapy, post-resection brachytherapy, and focused ultrasound. New targeted therapies and immunotherapies with documented intracranial activity have transformed clinical outcomes. Novel systemic therapies with intracranial utility include new anaplastic lymphoma kinase inhibitors like brigatinib and ensartinib; selective "rearranged during transfection" inhibitors like selpercatinib and pralsetinib; B-raf proto-oncogene inhibitors like encorafenib and vemurafenib; Kirsten rat sarcoma viral oncogene inhibitors like sotorasib and adagrasib; ROS1 gene rearrangement (ROS1) inhibitors, anti-neurotrophic tyrosine receptor kinase agents like larotrectinib and entrectinib; anti-human epidermal growth factor receptor 2/epidermal growth factor receptor exon 20 agent like poziotinib; and antibody-drug conjugates like trastuzumab-emtansine and trastuzumab-deruxtecan. This review highlights the modern multidisciplinary management of BM, emphasizing the integration of systemic and local therapies.

Molecular Pathways and Mechanisms of HER2 in Cancer Therapy

The oncogene ERBB2 encoding the receptor tyrosine-protein kinase erbB-2 (HER2) is frequently overexpressed or amplified and occasionally mutated in a variety of human cancers. The early discovery of this oncogene, its established oncogenic relevance in diverse cancers, its substantial expression on the surface of cancer cells, and its druggable catalytic activity have made it one of the most pursued targets in the history of cancer drug development. Initiatives targeting HER2 provided the early stimulus for several transformational pharmaceutical technologies, including mAbs, tyrosine kinase inhibitors, antibody-drug conjugates, and others. The seismic impact of these efforts has been felt in treatment of many cancers, including breast, gastroesophageal, lung, colorectal, and others. This impact continues to broaden with increasing indications on the horizon and a plethora of novel agents in development. However, implementation of these therapeutic strategies has been complex. The clinical translation of every one of these classes of agents has been notable for underperformance or overperformance characteristics that have informed new lines of research providing deeper insights into the mechanistic complexities and unrealized opportunities provided by this molecular target. Despite all the successes to date, the preponderance of scientific evidence indicates that the full potential of HER2 as a target for cancer therapeutics is far greater than currently realized, and numerous lines of investigation are ongoing to deepen and broaden the scope of impact of HER2 as a signaling, homing, or immunologic target. In this review, we explore the existing data and evolving paradigms surrounding this remarkable target for cancer therapy.

A Phase II Single-arm Study of Palbociclib in Patients With HER2-positive Breast Cancer With Brain Metastases and Analysis of ctDNA in Patients With Active Brain Metastases

INTRODUCTION

Palbociclib is highly efficacious and well tolerated in hormone-receptor positive (HR+) metastatic breast cancer (BC) but its activity for HER2+ BC with brain metastases (BM) is unknown.

METHODS

In a single-arm phase II study we evaluated palbociclib with trastuzumab for patients with HER2+ MBC and BM. The primary endpoint was BM response rate. Circulating tumor DNA (ctDNA) was evaluated at baseline, and in a subset of patients at cycle 3 and progression. We also retrospectively identified additional patients with metastatic BC, active BM, and a ctDNA assessment prior to therapy for BM.

RESULTS

Twelve patients with HER2+ MBC were enrolled, 4 with HR+ and 8 with HR- disease. No responses were seen. Best response was stable disease for 6 patients and progressive disease for 6 patients. The median PFS was 2.2 months, interquartile range (IQR) was 1.56 to 3.63 months. The median OS was 13.1 months and IQR was 9.4 to 23.8 months The CNS was the primary site of progression for all patients. The median variant allele fraction (VAF) of the dominant variant in each patient was 0.18% (interquartile range [IQR] 0.12%-0.47%) with a median number of somatic alterations of 1. We additionally evaluated ctDNA results from 26 patients with BC and active BM, among whom the median VAF was 11.8% (IQR 3.9%-27.3%) with a median number of alterations was 6 (IQR 4-9). Notably, progressive systemic disease was significantly less frequent in the trial cohort compared with additional retrospectively identified patients (8% vs. 81%).

CONCLUSION

Palbociclib did not demonstrate activity in HER2+ MBC with BM. Patients with progressive BM but stable, responding, or absent systemic disease have low VAF and number of alterations detected by ctDNA analysis from blood.

Epidemiology, clinical outcomes, and unmet needs of patients with human epidermal growth factor receptor 2-positive breast cancer and brain metastases: A systematic literature review

BACKGROUND

There is an increasing need for developing effective therapies for managing intracranial disease in patients with human epidermal growth factor receptor 2-positive (HER2 +) metastatic breast cancer and brain metastases (BM), as this population is growing and has historically been excluded from large clinical trials. In this systematic literature review, we aimed to provide a comprehensive overview of the epidemiology, unmet needs, and global treatment landscape for patients with HER2 + metastatic breast cancer and BM, with a particular focus on heterogeneity across clinical trial designs in this setting.

METHODS

We conducted literature searches of PubMed and select congress websites up to March 2022 and filtered for publications with a significant focus on epidemiology, unmet needs, or treatment outcomes in patients with HER2 + metastatic breast cancer and BM.

RESULTS

Key clinical trials of HER2-targeting treatments for HER2 + metastatic breast cancer had varying eligibility criteria relating to BM, with only two trials-HER2CLIMB and DEBBRAH-including patients with both active and stable BM. We also observed variance across assessed central nervous system (CNS)-focused endpoints (CNS objective response rate vs CNS progression-free survival vs time to CNS progression) and robustness of statistical analysis (prespecified vs exploratory).

CONCLUSIONS

There is an unmet need for standardization of clinical trial design for patients with HER2 + metastatic breast cancer and BM, to aid the interpretation of the global treatment landscape and ensure patients with all types of BM can access effective treatments.

Trastuzumab emtansine vs lapatinib and capecitabine in HER2-positive metastatic breast cancer brain metastases: A real-world study

BACKGROUND

Trastuzumab emtansine (T-DM1) has demonstrated improvements in survival and neurological symptoms in patients with breast cancer with brain metastases (BCBM). This real-world study investigated the effectiveness of T-DM1 versus lapatinib plus capecitabine (LC) in patients with BCBM.

METHODS

This retrospective, observational study evaluated patients with HER2-positive BCBM using a real-world database. Eligible patients had initiated T-DM1 or LC with a prior diagnosis of brain metastasis and ≥1 prior metastatic breast cancer treatment. The primary endpoint was overall survival (OS); secondary endpoints were time to next relevant treatment or death (TTNT) and real-world progression-free survival (rwPFS). An inverse probability of treatment weighting (IPTW) approach was used to account for differences in potential baseline characteristics between treatment groups. Outcomes were described using the Kaplan-Meier method, and the average treatment effect of initiating T-DM1 versus LC was estimated using weighted Cox proportional hazard models and hazard ratio (HR).

RESULTS

A total of 214 patients were available for analysis (T-DM1, n = 161; LC, n = 53). Demographics and baseline characteristics were generally well-balanced between treatment groups after weighting. After weighting, median OS was 17.7 (T-DM1) versus 9.6 (LC) months (HR, 0.55 [95% CI, 0.34-0.89]; P=0.013). Median TTNT was 9.0 (T-DM1) versus 6.0 (LC) months (HR, 0.55 [95% CI, 0.36-0.85]; P = 0.005). After weighting, median rwPFS was 6.0 (T-DM1) versus 4.0 (LC) months (HR, 0.50 [95% CI, 0.36-0.69]; P < 0.001).

CONCLUSIONS

These results support the superior effectiveness and clinical relevance of T-DM1 versus LC in patients with HER2-positive BCBM in the real world.

Systemic Therapy for Patients with HER2-Positive Breast Cancer and Brain Metastases: A Systematic Review and Meta-Analysis

AIM

Patients with HER2-positive (HER2+) metastatic breast cancer (mBC) develop brain metastases (BM) in up to 30% of cases. Treatment of patients with BM can consist of local treatment (surgery and/or radiotherapy) and/or systemic treatment. We undertook a systematic review and meta-analysis to determine the effect of different systemic therapies in patients with HER2+ mBC and BM.

METHODS

A systematic search was performed in the databases PubMed, Embase.com, Clarivate Analytics/Web of Science Core Collection and the Wiley/Cochrane Library. Eligible articles included prospective or retrospective studies reporting on the effect of systemic therapy on objective response rate (ORR) and/or median progression free survival (mPFS) in patients with HER2+ mBC and BM. The timeframe within the databases was from inception to 19 January 2022. Fixed-effects meta-analyses were used. Quality appraisal was performed using the ROBINS-I tool.

RESULTS

Fifty-one studies were included, involving 3118 patients. Most studies, which contained the largest patient numbers, but also often carried a moderate-serious risk of bias, investigated lapatinib and capecitabine (LC), trastuzumab-emtansine (T-DM1) or pyrotinib. The best quality data and/or highest ORR were described with tucatinib (combined with trastuzumab and capecitabine, TTC) and trastuzumab-deruxtecan (T-DXd). TTC demonstrated an ORR of 47.3% in patients with asymptomatic and/or active BM. T-DXd achieved a pooled ORR of 64% (95% CI 43-85%, I² 0%) in a heavily pretreated population with asymptomatic BM (3 studies, n = 96).

CONCLUSIONS

Though our meta-analysis should be interpreted with caution due to the heterogeneity of included studies and a related serious risk of bias, this review provides a comprehensive overview of all currently available systemic treatment options. T-Dxd and TTC that appear to constitute the most effective systemic therapy in patients with HER2+ mBC and BM, while pyrotinib might be an option in Asian patients.

Impact of epilepsy and its treatment on brain metastasis from solid tumors: A retrospective study

Introduction

Retrospective observational study on medical records of patients with epilepsy related brain metastases (BM) to evaluate efficacy, safety and possible interaction with cancer treatment of different anti-seizure medications (ASMs) and the risk of seizures.

Materials and methods

We consecutively reviewed all medical records of epilepsy-related BM patients from 2010 to 2020 who were followed for at least one month at the Brain Tumour-related Epilepsy Center of the IRCCS Regina Elena National Cancer Institute Rome, Italy.

Results

We selected 111 cancer patients. Of these, only 42 had at least undergone a second neurological examination. In the whole population, 95 (85.2%) had seizures and 16 patients had no seizures (14.4%). The most frequently first ASM prescribed was LEV (40.5%). We observed a significant correlation between tumor site and probability of having seizures, but not between seizure type and age (>65 or <65 years). Among 42 patients, 26 were administered levetiracetam, followed by oxcarbazepine. Until the last follow-up, 19 never changed the first ASM, maintained the same dosage and remained seizure free. After a median of 7 months, 16 (38.1%) required changes in therapeutic treatment due to inefficacy. At the last follow-up, 24 patients (57.1%) were seizure free. Eighteen patients (42.8%) never achieved freedom from seizures despite had at least 2 therapy changes. Two patients changed ASM due to adverse events and 1 to phenobarbital owing to the interaction with cancer treatment. The mean daily dose of first ASM in all 42 patients was very close to the Defined Daily Dose (DDD).

Conclusion

In BM patients seizure incidence could be underestimated; a team evaluation performed by oncologist and neurologist together, could guarantee an accurate taking care of both oncological illness and epilepsy, in this fragile patient population. More than 50% of our patients respond to monotherapy with new generation ASMs. Furthermore we deemed in patients receiving chemotherapy the choice of ASM should consider possible interactions with antitumor therapies, for this reason newer generation ASMs should be the preferred choice. It is necessary to get close to the DDD before considering an ASM ineffective in seizure control.

Advances in the Management of Central Nervous System Metastases from Breast Cancer

Central nervous system (CNS) metastases are common in breast cancer (BC) patients and are particularly relevant as new treatments for BC are prolonging survival. Here, we review advances in the treatment of CNS metastases from BC, including radiotherapy, systemic therapies, and the evolving role of immunotherapy. The use of radiotherapy and chemotherapy is the cornerstone of treatment for CNS metastases. However, new targeted therapies have recently been developed, including anti-HER2 agents and antibody-drug conjugates that have presented promising results for the treatment of these patients.

Current challenges and unmet needs in treating patients with human epidermal growth factor receptor 2-positive advanced breast cancer

Human epidermal growth factor receptor 2 oncogene (HER2-positive) overexpression/amplification occurs in less than 20% of breast cancers and has traditionally been associated with poor prognosis. Development of therapies that target HER2 has significantly improved outcomes for patients with HER2-positive advanced breast cancer (ABC). Currently available HER2-targeted agents include the monoclonal antibodies trastuzumab, pertuzumab, and margetuximab, the small-molecule inhibitors lapatinib, tucatinib, neratinib, and pyrotinib, as well as the antibody-drug conjugates trastuzumab emtansine and trastuzumab deruxtecan. Optimal sequencing of these agents in the continuum of the disease is critical to maximize treatment outcomes. The large body of clinical evidence generated over the past 2 decades aids clinicians in treatment decision-making. However, patients with HER2-positive ABC and specific disease characteristics and/or comorbidities, such as leptomeningeal disease, brain metastases, or cardiac dysfunction, are generally excluded from large randomized clinical trials, and elderly or frail patients are often underrepresented. In addition, there is great inequality in the accessibility of approved drugs across countries. This article addresses various challenging clinical situations when treating patients with HER2-positive ABC. The objective is to provide guidance to clinicians on how and when HER2-targeted therapies and additional treatments can be best implemented in routine clinical practice, on the basis of existing clinical evidence and expert opinion where needed.

Efficacy of tyrosine kinase inhibitors for the treatment of patients with HER2-positive breast cancer with brain metastases: a systematic review and meta-analysis

Background

Brain metastases (BMs) are frequent events in patients with HER2-positive metastatic breast cancer (MBC) and are associated with poor prognosis. Small-molecule anti-HER2 tyrosine kinase inhibitors (TKIs) are promising agents for the treatment of BM. In this study, we assess the clinical outcomes of patients with HER2-positive MBC and BM treated with TKI-containing regimens compared with those treated with non-TKI-containing regimens.

Materials and methods

PubMed, Embase, Cochrane Library, and conference proceedings (ASCO, SABCS, ESMO, and ESMO Breast) were searched up to June 2021. The primary endpoint was progression-free survival (PFS) in patients with BM. Secondary endpoints included PFS in patients without BM and overall survival (OS). The study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Overall effects were pooled using random-effects models.

Results

This systematic review and meta-analysis included data from 2437 patients (490 with and 1947 without BM at baseline) enrolled in five trials assessing tucatinib-, lapatinib-, pyrotinib-, or afatinib-based combinations. A nonstatistically significant PFS benefit favoring TKI-containing regimens was observed in both patients with BM [hazard ratio (HR) 0.67, 95% confidence interval (CI) 0.41-1.12; P = 0.13] and without BM (HR 0.55, 95% CI 0.24-1.26; P = 0.16). Sensitivity analysis, excluding each study singly, demonstrated a significant PFS benefit favoring TKI-containing regimens in patients with BM after the exclusion of afatinib from the analysis (HR 0.56, 95% CI 0.35-0.90; P = 0.016). No statistically significant differences in OS were observed between the comparison groups.

Conclusions

A trend in PFS favoring TKI-containing regimens was observed in patients with BM. Sensitivity analysis including only trials that evaluated regimens containing tucatinib, lapatinib, or pyrotinib demonstrated a significant PFS benefit favoring TKI-containing regimens in patients with BM.

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The optimal therapy for HER2+ BC BMs remains unknown.

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Anti-HER2 TKIs are effective for treating MBC.

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This study examined the efficacy of TKI for the treatment of patients with BM.

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A trend toward improved PFS favoring TKIs was observed in patients with BM.

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There was no significant difference in OS between TKIs versus non-TKI regimens.

Intracranial Response Rate in Patients with Breast Cancer Brain Metastases after Systemic Therapy

Simple Summary

For many years, patients with breast cancer and brain metastases were excluded from participation in clinical trials. It was believed that anticancer drugs could not cross the blood–brain barrier. However, recent evidence strongly suggests that some drugs can act against brain metastases, with the greatest intracranial response rate reported in the case of capecitabine, neratinib plus capecitabine, trastuzumab deruxtecan and tucatinib plus trastuzumab and capecitabine. In this article, we discuss the achievements in systemic therapy of breast cancer patients with brain metastases. We stress on the newest clinical trial results which indicate tremendous progress in HER2-positive breast cancer. On the other hand, in patients with triple-negative breast cancer or hormone-receptor-positive brain metastases, much fewer compounds were discovered. Based on the presented results, patients with active brain metastases should be routinely included in clinical trials with novel agents.

Abstract

Brain metastases are detected in 5% of patients with breast cancer at diagnosis. The rate of brain metastases is higher in HER2-positive and triple-negative breast cancer patients (TNBC). In patients with metastatic breast cancer, the risk of brain metastases is much higher, with up to 50% of the patients having two aggressive biological breast cancer subtypes. The prognosis for such patients is poor. Until recently, little was known about the response to systemic therapy in brain metastases. The number of trials dedicated to breast cancer with brain metastases was scarce. Our review summarizes the current knowledge on this topic including very significant results of clinical trials which have been presented very recently. We focus on the intracranial response rate of modern drugs, including new antibody–drug conjugates, HER2- targeted tyrosine kinase inhibitors and other targeted therapies. We highlight the most effective and promising drugs. On the other hand, we also suggest that further efforts are needed to improve the prognosis, especially patients with TNBC and brain metastases. The information contained in this article can help oncologists make treatment-related decisions.

Blood-Brain Barrier in Brain Tumors: Biology and Clinical Relevance

The presence of barriers, such as the blood–brain barrier (BBB) and brain–tumor barrier (BTB), limits the penetration of antineoplastic drugs into the brain, resulting in poor response to treatments. Many techniques have been developed to overcome the presence of these barriers, including direct injections of substances by intranasal or intrathecal routes, chemical modification of drugs or constituents of BBB, inhibition of efflux pumps, physical disruption of BBB by radiofrequency electromagnetic radiation (EMP), laser-induced thermal therapy (LITT), focused ultrasounds (FUS) combined with microbubbles and convection enhanced delivery (CED). However, most of these strategies have been tested only in preclinical models or in phase 1–2 trials, and none of them have been approved for treatment of brain tumors yet. Concerning the treatment of brain metastases, many molecules have been developed in the last years with a better penetration across BBB (new generation tyrosine kinase inhibitors like osimertinib for non-small-cell lung carcinoma and neratinib/tucatinib for breast cancer), resulting in better progression-free survival and overall survival compared to older molecules. Promising studies concerning neural stem cells, CAR-T (chimeric antigen receptors) strategies and immunotherapy with checkpoint inhibitors are ongoing.

Central Nervous System Metastases

The proportion of patients developing central nervous system (CNS) metastasis is increasing. Most are identified once symptomatic. Surgical resection is indicated for solitary or symptomatic brain metastases, separation surgery for compressive radioresistant spinal metastases, and instrumentation for unstable spinal lesions. Surgical biopsies are performed when histological diagnoses are required. Stereotactic radiosurgery is an option for limited small brain metastases and radioresistant spinal metastases. Whole-brain radiotherapy is reserved for extensive brain metastases and leptomeningeal disease with approaches to reduce cognitive side effects. Radiosensitive and inoperable spinal metastases typically receive external beam radiotherapy. Systemic therapy is increasingly being utilized for CNS metastases.

Pertuzumab Plus High-Dose Trastuzumab in Patients With Progressive Brain Metastases and HER2-Positive Metastatic Breast Cancer: Primary Analysis of a Phase II Study

PURPOSE

Effective therapies are needed for the treatment of patients with human epidermal growth factor receptor-2 (HER2)-positive metastatic breast cancer (MBC) with brain metastases. A trastuzumab radioisotope has been shown to localize in brain metastases of patients with HER2-positive MBC, and intracranial xenograft models have demonstrated a dose-dependent response to trastuzumab.

METHODS

In the phase II PATRICIA study (ClinicalTrials.gov identifier: NCT02536339), patients with HER2-positive MBC with CNS metastases and CNS progression despite prior radiotherapy received pertuzumab plus high-dose trastuzumab (6 mg/kg weekly) until CNS or systemic disease progression or unacceptable toxicity. The primary end point was confirmed objective response rate (ORR) in the CNS per Response Assessment in Neuro-Oncology Brain Metastases criteria. Secondary end points included duration of response, clinical benefit rate (complete response plus partial response plus stable disease ≥ 4 or ≥ 6 months) in the CNS, and safety.

RESULTS

Thirty-nine patients were treated for a median (range) of 4.5 (0.3-37.3) months at clinical cutoff. Thirty-seven patients discontinued treatment, most commonly because of CNS progression (n = 27); two remained on treatment. CNS ORR was 11% (95% CI, 3 to 25), with four partial responses (median duration of response, 4.6 months). Clinical benefit rate at 4 months and 6 months was 68% and 51%, respectively. Two patients permanently discontinued study treatment because of adverse events (left ventricular dysfunction [treatment-related] and seizure, both grade 3). No grade 5 adverse events were reported. No new safety signals emerged with either agent.

CONCLUSION

Although the CNS ORR was modest, 68% of patients experienced clinical benefit, and two patients had ongoing stable intracranial and extracranial disease for > 2 years. High-dose trastuzumab for HER2-positive CNS metastases may warrant further study.

Efficacy and safety of trastuzumab emtansine in older patients with HER2-positive advanced breast cancer: a real-world study

INTRODUCTION

Ado-trastuzumab emtansine (T-DM1) is an antibody-drug conjugate and its survival advantage has been shown in advanced human epidermal growth factor receptor 2 (HER2)-positive breast cancer. However, clinical trials underrepresent patients ⩾65 years of age, leading to a lack of information in this population. We analyzed the real-world outcomes of older women who were treated with T-DM1 therapy.

METHODS

We performed a multicenter, observational, retrospective analysis of patients aged ⩾65 years treated with T-DM1. A total of 93 patients from 10 cancer centers were involved in the study. Our goal was to determine the survival, response rates, and toxicity profile in T-DM1-treated patients, as well as the factors that influence survival.

RESULTS

Median follow-up was 12.2 months. Objective response rate was 29%. Median progression-free survival (PFS) and overall survival (OS) were 8.47 and 15.0 months, respectively. In multivariate analysis, Eastern Cooperative Oncology Group Performance Score 2 was found to be an independent prognostic factor for worse PFS (hazard ratio [HR] 1.81, p = 0.032) and OS (HR 2.33, p = 0.006). Any adverse event (AE) was seen in 92.5% of patients; grade 3 or 4 AEs were seen in 30.1%. Dose reduction or treatment discontinuation rates were 11.8% and 6.5%, respectively.

CONCLUSION

The efficacy of T-DM1 was acceptable and it was generally well-tolerated among older patients with advanced HER2-positive breast cancer.

HER-2 Neu gene: A valuable therapeutic target in metastatic mucoepidermoid carcinoma

INTRODUCTION

Salivary gland neoplasms (SGNs) respond poorly to the traditional chemotherapy agents limiting the availability of systemic treatment options in the metastatic setting. The recent identification of actionable molecular targets in SGNs has led to the evaluation of targeted therapies in non-approved advanced SGNs.

CASE REPORT

We present the case of an elderly male with HER-2 Neu overexpressing metastatic mucoepidermoid carcinoma (MEC) who demonstrated a prompt and sustained disease response to targeted therapies directed against HER-2 Neu with long survival interrupted by hepatoxicity to Trastuzumab emtansine (TDM-1) treatment.Management and Outcome: The patient was started on Trastuzumab and Pertuzumab on a clinical trial and resulted in an objective improvement sustained over 3 years. Following the disease progression, TDM-1 was started with a response until the patient developed severe hepatotoxicity as an adverse effect of TDM-1 therapy resulting in its discontinuation. Close follow-up post-treatment-discontinuation demonstrated continued clinical improvement until 6 months, when the patient developed brain metastasis. He passed away a few months later in hospice care.

DISCUSSION

The metastatic MEC in our patient overexpressed HER-2 Neu. Owing to Trastuzumab and Pertuzumab response, Trastuzumab emtansine (TDM-1) was initiated on a compassionate basis which further extended the survival but had to be terminated owing to adverse effects. Given the paucity of data on targeted therapies in the treatment of metastatic SGNs and the safety, tolerability, and efficacy of TDM-1 therapy among the elderly, further studies are warranted to answer these important questions and to identify eligible patients for this novel treatment option.

Brain Metastases in HER2-Positive Breast Cancer: Current and Novel Treatment Strategies

Development of brain metastases can occur in up to 30-50% of patients with breast cancer, representing a significant impact on an individual patient in terms of survival and quality of life. Patients with HER2-positive breast cancer have an increased risk of developing brain metastases; however, screening for brain metastases is not currently recommended due to the lack of robust evidence to support survival benefit. In recent years, several novel anti-HER2 agents have led to significant improvements in the outcomes of HER2-positive metastatic breast cancer. Despite these advances, brain and leptomeningeal metastases from HER2-positive breast cancer remain a significant cause of morbidity and mortality, and their optimal management remains an unmet need. This review presents an update on the current and novel treatment strategies for patients with brain metastases from HER2-positive breast cancer and discusses the open questions in the field.

Current treatment options for HER2-positive breast cancer patients with brain metastases

Brain metastases (BMs) are frequently associated with HER2+ breast cancer (BC). Their management is based on a multi-modal strategy including both local treatment and systemic therapy. Despite therapeutic advance, BMs still have an adverse impact on survival and quality of life and the development of effective systemic therapy to prevent and treat BMs from HER2 + BC represents an unmet clinical need. Trastuzumab-based therapy has long been the mainstay of systemic therapy and over the last two decades other HER2-targeted agents including lapatinib, pertuzumab and trastuzumab emtansine, have been introduced in the clinical practice. More recently, novel agents such as neratinib, tucatinib and trastuzumab deruxtecan have been developed, with interesting activity against BMs. Further research is needed to better elucidate the best sequence of these agents and their combination with local treatment.

Targeting the autophagy promoted antitumor effect of T-DM1 on HER2-positive gastric cancer

Trastuzumab emtansine (T-DM1), an antibody-drug conjugate consisted of the HER2-targeted monoclonal antibody trastuzumab and the tubulin inhibitor emtansine, has shown potent therapeutic value in HER2-positive breast cancer (BC). However, a clinical trial indicated that T-DM1 exerts a limited effect on HER2-positive gastric cancer (GC), but the underlying mechanism is inconclusive. Our research attempted to reveal the probable mechanism and role of autophagy in T-DM1-treated HER2-positive GC. In this study, our results showed that T-DM1 induced apoptosis and exhibited potent therapeutic efficacy in HER2-positive GC cells. In addition, autophagosomes were observed by transmission electron microscopy. Autophagy was markedly activated and exhibited the three characterized gradations of autophagic flux, consisting of the formation of autophagosomes, the fusion of autophagosomes with lysosomes, and the deterioration of autophagosomes in autolysosomes. More importantly, autophagic inhibition by the suppressors 3-methyladenine (3-MA) and LY294002 significantly potentiated cytotoxicity and apoptosis in HER2-positive GC cells in vitro, while the combined use of LY294002 and T-DM1 elicited potent anti-GC efficacy in vivo. In mechanistic experiments, immunoblot analysis indicated the downregulated levels of Akt, mTOR, and P70S6K and confocal microscopy analysis clearly showed that autophagic inhibition promoted the fusion of T-DM1 molecules with lysosomes in GC cells. In conclusion, our research demonstrated that T-DM1 induced apoptosis as well as cytoprotective autophagy, and autophagic inhibition could potentiate the antitumor effect of T-DM1 on HER2-positive GC. Furthermore, autophagic inhibition might increase the fusion of T-DM1 with lysosomes, which might accelerate the release of the cytotoxic molecule emtansine from the T-DM1 conjugate. These findings highlight a promising therapeutic strategy that combines T-DM1 with an autophagy inhibitor to treat HER-positive GC more efficiently.

Targeted Therapies for Breast Cancer Brain Metastases

The management of breast cancer, the most common cancer in the female population, has changed dramatically over years with the introduction of newer therapies. An increased incidence of brain metastases in recent years has created a challenge for oncologists because this population continues to have a poorer prognosis compared to metastatic breast cancer without central nervous system involvement. Historically, the exclusion of breast cancer patients with brain metastases from clinical trials has made treatment options even more limited. Nonetheless, more recently, this unmet need has been recognized by basic and clinical researchers and has led to the development of targeted therapies with better blood-brain barrier penetration and intracranial efficacy. Here we review targeted therapies directed at human epidermal growth factor receptor type 2 (HER2), vascular endothelial growth factor (VEGF), mammalian target of rapamycin (mTOR), epidermal growth factor receptor (EGFR), cyclin-dependent kinase 4 and 6 (CDK4/6) and poly(ADP-ribose) polymerase (PARP) for breast cancer patients with brain metastases. These therapies aim to be more efficacious and less toxic to represent a paradigm shift in the management of breast cancer brain metastases.

Trastuzumab emtansine (T-DM1) as adjuvant treatment of HER2-positive early breast cancer: safety and efficacy

Introduction: The prognosis of patients with HER2-positive early breast cancer has radically improved after the introduction of (neo)adjuvant anti-HER2 targeted therapy. Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate combining the anticancer properties of the anti-HER2 agent trastuzumab and the antineoplastic cytotoxic drug DM1. After demonstrating to be an effective and safe treatment for patients with HER2-positive advanced breast cancer, the development of T-DM1 has moved to the early setting.Areas covered: The aim of this review is to explore the current role of T-DM1 in the treatment landscape of HER2-positive early breast cancer, focusing specifically on the efficacy and safety data available in the adjuvant setting.Expert opinion: T-DM1 is an effective and safe treatment option in the adjuvant setting for patients with HER2-positive breast cancer without pathologic complete response after standard neoadjuvant chemotherapy plus anti-HER2 targeted therapy. With the availability of more effective anti-HER2 targeted agents, including T-DM1, there is an urgent need for more chemotherapy de-escalation research efforts in the early setting.

Dose-reduced trastuzumab deruxtecan can be safely used in liver failure and active leptomeningeal metastases

Trastuzumab deruxtecan has been shown to have responses in heavily pretreated patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer. However, the safety of this medication in patients with severe liver dysfunction and untreated or symptomatic central nervous system metastases is unknown. We describe a patient with metastatic HER2-positive breast cancer with liver failure and leptomeningeal metastases who was treated with dose-reduced trastuzumab deruxtecan. With treatment, the patient’s hyperbilirubinemia resolved and she demonstrated a response on imaging. She was dose-escalated to full dose with minimal adverse events.

HER2 antibody-drug conjugate controls growth of breast cancer brain metastases in hematogenous xenograft models, with heterogeneous blood-tumor barrier penetration unlinked to a passive marker

BACKGROUND

Brain metastases of HER2+ breast cancer persist as a clinical challenge. Many therapeutics directed at human epidermal growth factor receptor 2 (HER2) are antibodies or antibody-drug conjugates (ADCs), and their permeability through the blood-tumor barrier (BTB) is poorly understood. We investigated the efficacy of a biparatopic anti-HER2 antibody-tubulysin conjugate (bHER2-ATC) in preclinical models of brain metastases.

METHODS

The compound was evaluated in 2 hematogenous HER2+ brain metastasis mouse models, SUM190-BR and JIMT-1-BR. Endpoints included metastasis count, compound brain penetration, cancer cell proliferation, and apoptosis.

RESULTS

Biparatopic HER2-ATC 3 mg/kg prevented metastasis outgrowth in the JIMT-1-BR model. At 1 mg/kg bHER2-ATC, a 70% and 92% reduction in large and micrometastases was observed. For the SUM190-BR model, an 85% and 53% reduction, respectively, in large and micrometastases was observed at 3 mg/kg, without statistical significance. Proliferation was reduced in both models at the highest dose. At the endpoint, bHER2-ATC uptake covered a median of 4-6% and 7-17% of metastasis area in the JIMT-1-BR and SUM190-BR models, respectively. Maximal compound uptake in the models was 19% and 86% in JIMT-1-BR and SUM190-BR, respectively. Multiple lesions in both models demonstrated ADC uptake in the absence or low diffusion of Texas Red Dextran, a marker of paracellular permeability. Using in vitro BTB assays, the ADC was endocytosed into brain endothelial cells, identifying a potentially new mechanism of antibody permeability.

CONCLUSIONS

Biparatopic HER2-ATC significantly prevented JIMT-1-BR brain metastasis outgrowth and showed activity in the SUM190-BR model. The bHER2-ATC penetration into metastases that are impermeable to fluorescent dye suggested an endocytic mechanism of brain penetration.

Local and systemic treatment for HER2-positive breast cancer with brain metastases: a comprehensive review

The management of human epidermal growth factor receptor (HER2)-positive breast cancer has improved over the past decade. However, despite improvements in systemic control, a substantial proportion of patients with advanced HER2-positive breast cancer suffer from central nervous system metastases and even intracranial progression after aggressive local treatment. There is paucity of data and no consensus on the systemic therapies for patients with intracranial progression. This review discusses both local and systemic treatments for HER2-positive breast cancer with brain metastases with a special focus on the response of central nervous system metastases. A recommended practical treatment algorithm to guide physicians in selecting the most appropriate anti-HER2 therapy for their patients is suggested.

Management of brain metastases according to molecular subtypes

The incidence of brain metastases has markedly increased in the past 20 years owing to progress in the treatment of malignant solid tumours, earlier diagnosis by MRI and an ageing population. Although local therapies remain the mainstay of treatment for many patients with brain metastases, a growing number of systemic options are now available and/or are under active investigation. HER2-targeted therapies (lapatinib, neratinib, tucatinib and trastuzumab emtansine), alone or in combination, yield a number of intracranial responses in patients with HER2-positive breast cancer brain metastases. New inhibitors are being investigated in brain metastases from ER-positive or triple-negative breast cancer. Several generations of EGFR and ALK inhibitors have shown activity on brain metastases from EGFR and ALK mutant non-small-cell lung cancer. Immune-checkpoint inhibitors (ICIs) hold promise in patients with non-small-cell lung cancer without druggable mutations and in patients with triple-negative breast cancer. The survival of patients with brain metastases from melanoma has substantially improved after the advent of BRAF inhibitors and ICIs (ipilimumab, nivolumab and pembrolizumab). The combination of targeted agents or ICIs with stereotactic radiosurgery could further improve the response rates and survival but the risk of radiation necrosis should be monitored. Advanced neuroimaging and liquid biopsy will hopefully improve response evaluation.

Safety and efficacy of T-DM1 in patients with advanced HER2-positive breast cancer The Royal Marsden experience

BACKGROUND

Ado-trastuzumab emtansine (T-DM1) is standard of care for patients with advanced HER2+ breast cancer who relapse within 6 months of adjuvant trastuzumab or progress on first-line anti-HER2 therapy. We evaluated its safety and efficacy in our real-world population.

METHODS

We identified patients on T-DM1 from 01/01/2014 to 12/03/2018 from our electronic records. Patients', tumour characteristics, safety and efficacy outcomes were recorded. Chi-squared/Fishers exact test and Kaplan-Meier methods were utilised.

RESULTS

128 patients receiving T-DM1 were included in the analysis with a median age of 55 years (26-85). 89.8% of patients had ECOG PS 0-1 and 21.1% had presented with de novo metastatic disease. 57.8% had ER-positive disease and 38.3% central nervous system involvement. 88.3% of patients had received trastuzumab for advanced disease (with pertuzumab in 28.9%) and 11.7% had only received trastuzumab in the adjuvant setting. Grade ≥3 adverse events occurred in 35.9% of patients. These were liver toxicity (19.5%), anaemia (6.2%) and thrombocytopenia (4.7%). Peripheral neuropathy of any grade was reported in 21.9% of cases, bleeding in 9.4% and ejection fraction decline in 5 patients. Median progression-free survival was 8.7 months and overall survival 20.4 months. Prior pertuzumab did not influence survival outcomes.

CONCLUSIONS

The safety of T-DM1 in our population is similar to available literature, although we observed higher rates of peripheral neuropathy and deranged liver function. These findings are relevant for the potential role of TDM-1 in the curative setting.

Prognostic factors and outcome of HER2+ breast cancer with CNS metastases

Aim: Trastuzumab prolongs progression-free and overall survival in HER2+ breast cancer (BC), but these are associated with increased distant recurrences and central nervous system metastases (CNSm). We retrospectively evaluated outcome and prognostic factors in CNSm and non-CNSm patients. Methods: Records of HER2+ BC treated in 2000-2017 were reviewed. Results: 283/1171 (24%) HER2+ BC patients developed metastatic disease. 109/283 patients (39%) have CNSm associated with worse prognosis and increased risk of death (hazard ratio: 4.7; 95% CI: 3.5-6.4). Prognostic factors were: number of CNSm (single vs multiple lesions; 3-year overall survival 39 vs 18%; p = 0.003); brain radiation (30 vs 14%; p < 0.001); new HER2-targeting therapies (30.6 vs 22.5%; p = 0.025). Conclusion: Prognosis of BC patients with CNSm has improved using HER2-targeting therapies but remains poor.

HER2-targeted therapy prolongs survival in patients with HER2-positive breast cancer and intracranial metastatic disease: a systematic review and meta-analysis

BACKGROUND

Intracranial metastatic disease (IMD) is a serious and known complication of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The role of targeted therapy for patients with HER2-positive breast cancer and IMD remains unclear. In this study, we sought to evaluate the effect of HER2-targeted therapy on IMD from HER2-positive breast cancer.

METHODS

We searched MEDLINE, EMBASE, CENTRAL, and gray literature sources for interventional and observational studies reporting survival, response, and safety outcomes for patients with IMD receiving HER2-targeted therapy. We pooled outcomes through meta-analysis and examined confounder effects through forest plot stratification and meta-regression. Evidence quality was evaluated using GRADE (PROSPERO CRD42020161209).

RESULTS

A total of 97 studies (37 interventional and 60 observational) were included. HER2-targeted therapy was associated with prolonged overall survival (hazard ratio [HR] 0.47; 95% confidence interval [CI], 0.39-0.56) without significantly prolonged progression-free survival (HR 0.52; 95% CI, 0.27-1.02) versus non-targeted therapy; the intracranial objective response rate was 19% (95% CI, 12-27%), intracranial disease control rate 62% (95% CI, 55-69%), intracranial complete response rate 0% (95% CI, 0-0.01%), and grade 3+ adverse event rate 26% (95% CI, 11-45%). Risk of bias was high in 40% (39/97) of studies.

CONCLUSION

These findings support a potential role for systemic HER2-targeted therapy in the treatment of patients with IMD from HER2-positive metastatic breast cancer.

Multidisciplinary patient-centered management of brain metastases and future directions

The incidence of brain metastasis is increasing as improvements in systemic therapy lead to increased survival. This provides new and challenging clinical decisions for patients who are trying to balance the risk of recurrence or progression with treatment-related side effects, and it requires appropriate management strategies from multidisciplinary teams. Improvements in prognostic assessment and systemic therapy with increasing activity in the brain allow for individualized care to better guide the use of local therapies and/or systemic therapy. Here, we review the current landscape of brain-directed therapy for the treatment of brain metastasis in the context of recent improved systemic treatment options. We also discuss emerging treatment strategies including targeted therapies for patients with actionable mutations, immunotherapy, modern whole-brain radiation therapy, radiosurgery, surgery, and clinical trials.

HER2-Overexpressing/Amplified Breast Cancer as a Testing Ground for Antibody-Drug Conjugate Drug Development in Solid Tumors

Efficacy data from the KATHERINE clinical trial, comparing the HER2-directed antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) to trastuzumab in patients with early-stage HER2-amplified/overexpressing breast cancer with residual disease after neoadjuvant therapy, demonstrates superiority of T-DM1 (HR for invasive disease or death, 0.50; P < 0.001). This establishes foundational precedent for ADCs as effective therapy for treatment of subclinical micrometastasis in an adjuvant (or post-neoadjuvant) early-stage solid tumor setting. Despite this achievement, general principles from proposed systems pharmacokinetic modeling for intracellular processing of ADCs indicate potential shortcomings of T-DM1: (i) C _max limited by toxicities; (ii) slow internalization rate; (iii) resistance mechanisms due to defects in intracellular trafficking [loss of lysosomal transporter solute carrier family 46 member 3, (SLC46A3)], and increased expression of drug transporters MDR1 and MRP1; and (iv) lack of payload bystander effects limiting utility in tumors with heterogeneous HER2 expression. These handicaps may explain the inferiority of T-DM1-based therapy in the neoadjuvant and first-line metastatic HER2⁺ breast cancer settings, and lack of superiority to chemotherapy in HER2⁺ advanced gastric cancer. In this review, we discuss how each of these limitations is being addressed by manipulating internalization and trafficking using HER2:HER2 bispecific or biparatopic antibody backbones, using site-specific, fixed DAR conjugation chemistry, and payload swapping to exploit alternative intracellular targets and to promote bystander effects. Newer HER2-directed ADCs have impressive clinical activity even against tumors with lower levels of HER2 receptor expression. Finally, we highlight ongoing clinical efforts to combine HER2 ADCs with other treatment modalities, including chemotherapy, molecularly targeted therapies, and immunotherapy.