The incidence of brain metastases among patients with metastatic breast cancer: a systematic review and meta-analysis

Therapeutic Ultrasound for Multimodal Cancer Treatment: A Spotlight on Breast Cancer

Cancer remains a leading cause of mortality worldwide, and the demand for improved efficacy, precision, and safety of management options has never been greater. Focused ultrasound (FUS) is a rapidly emerging strategy for nonionizing, noninvasive intervention that holds promise for the multimodal treatment of solid cancers. Owing to its versatile array of bioeffects, this technology is now being evaluated across preclinical and clinical oncology trials for tumor ablation, therapeutic delivery, radiosensitization, sonodynamic therapy, and enhancement of tumor-specific immune responses. Given the breadth of this burgeoning domain, this review places a spotlight on recent advancements in breast cancer care to exemplify the multifaceted role of FUS technology for oncology indications-outlining physical principles of FUS-mediated thermal and mechanical bioeffects, giving an overview of results from recent preclinical and clinical studies investigating FUS with and without adjunct therapeutics in primary or disseminated breast cancer settings, and offering perspectives on the future of the field.

GRB2 promotes brain metastasis in HER2-positive breast cancer by regulating the Ras/MAPK pathway

Brain metastasis is emerging as the most serious concern for breast cancer patients. HER2-positive breast cancer is more prone to undergo brain metastasis than other subtypes; notably, there has been little improvement in the treatment of brain metastasis .Our study confirmed the relevance of HER2 status to brain metastasis risk via clinical data analysis and revealed that exerts GRB2 tumorigenic effects by regulating the Ras/MAPK pathway in vivo and in vitro. Both an in situ injection model and a direct cerebral injection model were used to explore the ability of GRB2 to promote the brain metastasis. Results indicated that HER2- positive is a risk factor for brain metastasis according to clinical data. GRB2 enhances proliferation, migration, and invasion while suppressing apoptosis in HER2-positive breast cancer cells in vitro, primarily by regulating phosphorylation and alternative splicing of key proteins within the Ras/MAPK pathway. Notably, tumor cells were able to cross the blood‒brain barrier in both models assessed in this study. Thus, GRB2 is an oncogenic factor that contributes to the malignancy of HER2-positive breast cancer, GRB2 and HER2 can synergistically promote tumor cell penetration of the blood‒brain barrier and induce metastasis.

Isoliquiritigenin reduces brain metastasis by circNAV3-ST6GALNAC5-EGFR axis in triple-negative breast cancer

Brain metastasis (BM) is a serious complication of increasing incidence in patients with advanced breast cancer, which is characterized by swift deterioration in quality of life with few efficient therapy strategies. There is an urgent clinical requirement to devise potent therapeutic strategies for the prevention and management of brain metastases. Here, we report isoliquiritigenin (ISL), a key bioactive substance extracted from licorice root, which effectively inhibited triple-negative breast cancer (TNBC) brain metastasis (BM) by downregulation of circNAV3. CircRNAs expression analyses and functional studies, coupled with clinical significance investigations identified circNAV3 as a key molecule promoting TNBC BM. Functionally, circNAV3 could promote proliferation, migration, invasion, angiogenesis and capacity to penetrate the blood-brain barrier of TNBC cells. Mechanistically, circNAV3 could competitively bind with miR-4262, hence intercepting the suppressive effect of miR-4262 on ST6GALNAC5. Subsequently, this interplay enhanced EGFR sialylation and activation, initiating the PI3K/Akt pathway and ultimately fostering the development of TNBC brain metastases. In conclusion, our research establishes that ISL impede the initiation and advancement of TNBC brain metastasis by modulation of circNAV3/miR-4262/ST6GALNAC5/EGFR axis, laying a theoretical groundwork for the therapeutic use of ISL in this scenario.

TUXEDO-4: phase II study of trastuzumab-deruxtecan in HER2-low breast cancer with new or progressing brain metastases

CLINICAL TRIAL REGISTRATION

NCT06048718 (clinicaltrials.gov); 2023 -506,702-39-00 (EudraCT number).

Investigation of Prevalence, Survival, and Molecular Type of Breast Cancer Patients with Brain Metastases

Background

This study aims to investigate the factors associated with breast cancer brain metastasis (BCBM) in individuals suffering from breast cancer (BC).

Materials and Methods

This cross-sectional study conducted on 200 patients with metastatic breast cancer (MBC) including 52 brain and 148 other organ metastases. The demographic, medical, clinical, laboratory, and therapeutic approach characteristics were compared between the groups.

Results

Headache (61.5%), weakness and lethargy (26.9%), dizziness (15.4%), blurred vision/blindness (15.4%), and convulsions (15.4%) were the major initial symptoms of BCBM. Radiotherapy (71.2%), injectable (34.6%), and oral chemotherapy (26.9%) were the major applied therapeutic strategies to manage brain metastasis (BM). The overall survival of the patients from cancer diagnosis to death accounted for 33 months (95%CI: 27.52-38.47), while this period after BM diagnosis was limited to 6 months (95%CI: 5.15-6.84). The rate of hormone therapy was remarkably higher among the metastasis in other organs than the brain (P value = 0.005), while targeted therapy was performed in higher rates for BM (P value = 0.001). The evaluation of BC-related tumor markers revealed that human epidermal growth factor 2 (HER2) (P value < 0.001) positivity was remarkably higher among BCBM, while positive estrogen receptor (ER) (P value = 0.004) and progesterone receptor (PR) (P value = 0.013) were statistically more in the other group.

Conclusion

Based on the findings of this study, the BC patients with BM had a remarkable short survival, had a higher rate of perineural invasion, and were mostly positive for HER2. Radiotherapy, chemotherapy, and surgery were the most common approaches to these patients.

Physiologically Based Pharmacokinetic Model of Plasma and Intracranial Pharmacokinetics and CDK4/6 Occupancy of Abemaciclib to Optimizing Dosing Regimen for Brain Metastatic Patients

Objective: The study aimed to develop a physiologically based pharmacokinetic (PBPK) model to predict steady state trough concentrations (C min) and CDK4/6 occupancy in plasma and cerebrospinal fluid (CSF) for abemaciclib (ABE) and its three active metabolites. Additionally, a biomarker model was constructed to simulate changes in pRB and TOPO-IIα expression. Methods: The population PBPK and biomarker models of ABE were developed using physicochemical, pharmacokinetics (PK), CDK4/6 occupancy, biomarker, and physiological properties. These models were then validated using four clinical plasma PK studies, two CSF PK studies, and one clinically observed biomarker expression change in patients. Results: The PBPK model showed good consistency with observed data, with most prediction-to-observation ratios falling within the range of 0.5 to 2.0 for AUC, C max, C min in plasma and CSF. Key factors affecting C min and CDK4/6 occupancy for total analytes (sum of ABE and metabolites) were identified as CYP3A4, ABCB1, ABCG2 expression, and plasma albumin levels. PBPK simulations suggested that the optimal dosing regimen for ABE in brain metastatic breast cancer (MBC) is either 150 or 200 mg twice daily (BID). Conclusions: The PBPK model successfully simulated the PK profiles and CDK4/6 occupancy for ABE and its three metabolites in plasma and CSD, and determined the optimal dosing in brain MBC. Overall,The PBPK model can provide important insights for personalized dosing strategies, contributing to improved treatment efficacy and safety for patients, particularly those with brain MBC.

Association Between Human Epidermal Growth Factor Receptor 2-Low Status and Time to Development of Brain Metastases Among Patients With Breast Cancer: A Retrospective Cohort Study

PURPOSE

Human epidermal growth factor receptor 2 (HER2)-low is a newly defined subgroup of HER2-negative breast cancer. It is unknown whether HER2-low status is associated with brain metastases (BrM) development. We aimed to determine the association between HER2-low status and the time to developing BrM.

METHODS

HER2 status was determined in a cohort of 689 women with metastatic breast cancer (MBC) who underwent treatment for BrM at Sunnybrook Odette Cancer Centre from 2008 to 2018. In patients with primary breast cancer (PBC) HER2 subclassification available (subgroup 1), we investigated time from PBC diagnosis to BrM diagnosis (PBC-time to brain metastases [TTBM]). In patients with HER2 subclassification available in any tissue (subgroup 2), we investigated time from MBC diagnosis to BrM diagnosis (MBC-TTBM).

RESULTS

In subgroup 1 (n = 175), patients with HER2-low disease (n = 42) had a shorter PBC-TTBM compared with those with HER2-zero disease (n = 77; hazard ratio, 2.4; P = .0003). When stratified by hormone receptor (HR) status, this observation held true in the HR+/HER2- population, but not in the triple-negative breast cancer (TNBC) population. In subgroup 2 (n = 279), patients with HER2-low disease (n = 53) had a shorter MBC-TTBM compared to those with HER2-zero disease (n = 44) in the HR+/HER2- population (hazard ratio, 1.55; P = .036); however, this did not hold true in the TNBC population. Likelihood ratio test revealed significant interaction between HER2 and HR status in subgroup 2 (P = .016), but not subgroup 1 (P = .21).

CONCLUSION

Our findings suggest that among patients with HR+ breast cancer, HER2-low status was associated with shorter TTBM compared with HER2-zero status. In a subset of patients for whom HER2 status of the PBC was available, HER2-low status was associated with shorter PBC-TTBM, irrespective of HR status. This study suggests a previously unrecognized association between HER2-low status and timing of BrM development.

Utilizing Vision Transformers for Predicting Early Response of Brain Metastasis to Magnetic Resonance Imaging-Guided Stage Gamma Knife Radiosurgery Treatment

BACKGROUND/OBJECTIVES

This study explores the application of vision transformers to predict early responses to stereotactic radiosurgery in patients with brain metastases using minimally pre-processed magnetic resonance imaging scans. The objective is to assess the potential of vision transformers as a predictive tool for clinical decision-making, particularly in the context of imbalanced datasets.

METHODS

We analyzed magnetic resonance imaging scans from 19 brain metastases patients, focusing on axial fluid-attenuated inversion recovery and high-resolution contrast-enhanced T1-weighted sequences. Patients were categorized into responders (complete or partial response) and non-responders (stable or progressive disease).

RESULTS

Despite the imbalanced nature of the dataset, our results demonstrate that vision transformers can predict early treatment responses with an overall accuracy of 99%. The model exhibited high precision (99% for progression and 100% for regression) and recall (99% for progression and 100% for regression). The use of the attention mechanism in the vision transformers allowed the model to focus on relevant features in the magnetic resonance imaging images, ensuring an unbiased performance even with the imbalanced data. Confusion matrix analysis further confirmed the model's reliability, with minimal misclassifications. Additionally, the model achieved a perfect area under the receiver operator characteristic curve (AUC = 1.00), effectively distinguishing between responders and non-responders.

CONCLUSIONS

These findings highlight the potential of vision transformers, aided by the attention mechanism, as a non-invasive, predictive tool for early response assessment in clinical oncology. The vision transformer (ViT) model employed in this study processes MRIs as sequences of patches, enabling the capture of localized tumor features critical for early response prediction. By leveraging patch-based feature learning, this approach enhances robustness, interpretability, and clinical applicability, addressing key challenges in tumor progression prediction following stereotactic radiosurgery (SRS). The model's robust performance, despite the dataset imbalance, underscores its ability to provide unbiased predictions. This approach could significantly enhance clinical decision-making and support personalized treatment strategies for brain metastases. Future research should validate these findings in larger, more diverse cohorts and explore the integration of additional data types to further optimize the model's clinical utility.

Targeted Modulation of the Meningeal Lymphatic Reverse Pathway for Immunotherapy of Breast Cancer Brain Metastases

Treatment of tumor brain metastases remains challenging due to the ineffectiveness of drugs in crossing the blood-brain barrier (BBB). Here, we proposed a potential strategy to target and modulate the meningeal lymphatic system for immunotherapy of breast cancer brain metastases (BCBM) through peripheral administration. CT/fluorescence dual-modality imaging demonstrated that the phospholipid nanoprobe (α-PLNPs) through intracisternal magna injection effectively labeled and long-range tracked the meningeal lymphatic pathway from meningeal lymphatic vessels (MLVs) to periphery drainage cervical lymph nodes (CLNs). Interestingly, the reverse pathway from CLNs to MLVs was also successfully labeled with α-PLNPs through cervical subcutaneous injection, facilitating the noninvasive delivery of immunomodulators to the meningeal lymphatics. Given this, we used melittin-carrying α-M-PLNPs to trigger the modulation of the meningeal lymphatic reverse pathway, which effectively prevents BCBM and prolongs the survival of mice through activating the antigen-presenting cells in the CLNs and promoting the migration of CD8+ T cells into the metastatic brain tumors. This study highlights the potential of the meningeal lymphatic reverse pathway for the immunotherapy of BCBM, which holds great promise for central nervous system disease therapy without the need for drug delivery via BBB.

Trastuzumab deruxtecan in human epidermal growth factor receptor 2-positive breast cancer brain metastases: A systematic review and updated meta-analysis

BACKGROUND

Trastuzumab deruxtecan (T-DXd) has shown promising activity in patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) and central nervous system (CNS) involvement. In this updated meta-analysis, we explore the effectiveness of T-DXd in a large subset of patients with HER2-positive BC and CNS disease.

METHODS

A systematic search was made on September 16th, 2024, for studies investigating T-DXd in the scenario of HER2-positive BC and brain metastases (BMs) and/or leptomeningeal disease (LMD). We used random effects models for all statistical analyses.

RESULTS

We included 18 studies with 786 HER2-positive BC patients with CNS involvement (16 studies with 750 BMs patients and three studies with 36 LMD patients). We observed high overall antitumor responses (objective response rate [ORR], 60.4 %; disease control rate [DCR], 94.4 %; and clinical benefit rate [CBR], 79.3 %) and a 12-month PFS of 64.7 % and OS of 82.7 %. Intracranial ORR, DCR, and CBR were seen in 62.2 %, 88.6 %, and 68.6 % of patients, respectively, and 67.4 % achieved intracranial PFS at 12 months. Both stable and active BMs subgroups derived similar benefit from T-DXd. Better intracranial responses were seen for 33 patients with untreated BMs compared to 56 patients with previously treated or progressing lesions (odds ratio 3.82, 95 % confidence interval 1.3-10.8, p = 0.01). For the LMD group, T-DXd elicited intracranial ORR and CBR in 59.4 % and 94.1 % of patients, respectively.

CONCLUSIONS

This updated meta-analysis continues to support the overall and intracranial activity of T-DXd in patients with HER2-positive BC and CNS involvement, including those with LMD.

Neurological symptom management in breast cancer meningeal carcinomatosis

No treatment has been established for meningeal carcinomatosis (MC) in advanced metastatic breast cancer, and its prognosis is poor. In recent years, systemic therapies such as trastuzumab deruxtecan and tucatinib have been reported effective for human epidermal growth factor receptor 2 (HER2)-positive breast cancer, however, these cannot be used for all MC. The difficulty in diagnosing and treating MC is attributed to its diverse pathology. As a result, in clinical practice, diagnosis is often delayed, and symptoms persist. This review focuses on whether neurological symptoms can be effectively alleviated even with unestablished treatments by classifying the pathology of MC into meningitis, hydrocephalus-related intracranial hypertension symptoms, focal brain damage such as epilepsy, cranial nerve disorders, and spinal cord symptoms and evaluating the diagnosis and condition. Hydrocephalus can be managed with drainage and ventriculoperitoneal shunt surgery, and meningitis symptoms and cranial nerve disorders can be managed with whole brain radiotherapy. Antiepileptic drugs are essential for epilepsy, and supportive care is necessary, as are steroids for cranial nerve disorders. However, MC is not caused by a single condition but can occur in combination thus the therapeutic effectiveness of palliative therapy for neurological symptoms is currently unknown, and research is limited. In the future, if a lineup of highly effective systemic therapies such as tyrosine kinase inhibitors for ALK gene-positive lung cancer is established, treatment strategies for MC may change. However at present, rapid diagnosis and prompt neurological palliative treatment play an important role in the neurological symptoms management of MC.

Prognostic Factors in Therapy Regimes of Breast Cancer Patients with Brain Metastases: A Retrospective Monocentric Analysis

Background: Breast cancer patients who develop brain metastases have a high mortality rate and a massive decrease in quality of life. Approximately 10-15% of all patients with breast cancer (BC) and 5-40% of all patients with metastatic BC develop brain metastasis (BM) during the course of the disease. However, there is only limited knowledge about prognostic factors in the treatment of patients with brain metastases in breast cancer (BMBC). Therefore, we retrospectively analyzed data of BMBC patients from the University Hospital of Würzburg for treatment patterns to find characteristics associated with a better or worse prognosis. These findings should help to treat the ever-increasing collective of patients with BMBC better in the future. Methods: The clinical data of 337 patients with cerebral metastatic breast cancer (date of death between 2004 and 2021) treated at the Department of Gynecology and Obstetrics of the University Hospital Würzburg were retrospectively analyzed, with a focus on patients' survival. Results: The involvement of regional lymph nodes at initial diagnosis, the immunohistochemical subtype of TNBC at the onset of BMBC, and extracranial metastases at the time of BM diagnosis (bone, liver, lung metastases) were associated with a worse prognosis. In contrast, the immunohistochemical subtype of HER2/neu, the sole occurrence of a singular BM, the local surgical removal of BMs, and radiotherapy (especially stereotactic radiotherapy) were associated with prolonged survival. The number of therapies before the diagnosis of BMs also had a prognostic influence. Conclusions: Looking back at data is crucial for pinpointing risk elements affecting survival after a BM diagnosis. In our investigation, along with established factors like immunohistologic subtype, BM count, surgical excision, stereotactic irradiation, and type of extracranial metastasis, we also found that the number of therapies before BM diagnosis and the initial lymph node status were associated with patients' survival. Potentially, these factors could be included in prospective prognostic scores for evaluating brain metastasis survival rates, thereby aiding in making appropriate treatment suggestions for impacted patients.

Analysis of HER2 expression changes from breast primary to brain metastases and the impact of HER2-low expression on overall survival

BACKGROUND

There are limited data regarding HER2-low expression dynamics between matched primary tumors and brain metastases (BrMs) in breast cancer. HER2-low expression has emerged as a new therapeutic biomarker for highly active antibody-drug conjugates with emerging intracranial activity.

METHODS

Patients with metastatic breast cancer and BrMs seen at an NCI-designated center between 2003 and 2023 were identified. HER2 expression was defined as HER2-positive (3+, 2+/ISH amplified), HER2-low (1+, 2+/ISH negative), or HER2-0 by ASCO-CAP guidelines. Estrogen receptor (ER) status was defined as ER ≥1%. Multivariate survival analyses by Cox proportional hazard models were determined from the time of BrM resection to death or last follow-up between the 3 subtypes, controlling for ER and age.

RESULTS

Among 197 matched primary and resected BrMs, 81% exhibited HER2 expression in the brain: 61% HER2-positive, 20% HER2-low, and 19% HER2-0. Concordance was high in HER2-positive primary tumors with 100% retaining HER2 expression (97% retained HER2-positive expression and 2.7% switched to HER2-low). HER2-0 primaries frequently showed HER2 gain in BrMs to HER2-low (35%) or HER2-positive (5.4%) status. Among 48 HER2-low primary tumors, 52% were discordant for HER2 status in the brain with 21% testing HER2-positive and 31% testing HER2-0. In adjusted analyses, patients with HER2-positive BrMs had significantly lower death risk than patients with HER2-low BrMs (HR = 0.41, P = .0006); no difference was observed between HER2-0 and HER2-low.

CONCLUSIONS

In this retrospective analysis, HER2 expression is common in breast cancer BrMs, emphasizing the need for improved, noninvasive diagnostics. Patients with HER2-low and HER2-0 BrMs face inferior survival, presenting an unmet clinical need.

Proton pump inhibitor attenuates acidic microenvironment to improve the therapeutic effects of MSLN-CAR-T cells on the brain metastasis

The incidence of brain metastasis (BM) is gradually increasing, and the prognosis and therapeutic effect are poor. The emergence of immunotherapy has brought hope for the development of BM treatments. This study revealed that compared with primary cancers, BMs have a colder and more acidic tumor microenvironment (TME), resulting in reduced protein levels of mesothelin (MSLN), a promising target for chimeric antigen receptor-T (CAR-T) cell therapy for triple-negative breast cancer (TNBC) with BMs. These factors could significantly decrease the efficiency of MSLN-CAR-T cells in TNBC BMs. Pantoprazole (PPZ) administration at the most commonly used dose in the clinic notably increased the pH of the TME, inhibited lysosomal activity, increased the membrane levels of the MSLN protein and improved the killing ability of MSLN-CAR-T cells both in vitro and in vivo. Similar results were obtained in non-small cell lung cancer BMs. Hence, when administered in combination with CAR-T cells, PPZ, which increases the protein levels of target antigens, may constitute a new immunotherapeutic strategy for treating solid tumors with BMs.

Intravenous liposomal irinotecan in metastatic triple-negative breast cancer after ≥ 2 prior lines of chemotherapy: a phase Ib study

This study (NCT04728035) aimed to explore the safety and efficacy of liposomal irinotecan (HE072) in patients with metastatic triple-negative breast cancer (mTNBC). This study consisted of two parts. In part 1, the 3 + 3 design was used to investigate three dose levels of HE072 (50, 70 and 90 mg/m2). In part 2, patients were enrolled in two cohorts (mTNBC and HER2-negative breast cancer brain metastasis [BCBM]), and received HE072 70 mg/m2 every two weeks (Q2W). The primary endpoints were maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D), and treatment emergent adverse events (TEAEs). The secondary endpoints were pharmacokinetic profiles and efficacy including objective response rate (ORR) and disease control rate (DCR) (all patients) and Central Nervous System ORR and clinical benefit rate (CBR, for patients with HER2-negative BCBM), duration of response, progression free survival (PFS), overall survival (OS). A total of 119 patients were enrolled, including 101 mTNBC and 18 HER2-negative BCBM. One dose limiting toxicity (grade 3 nausea and vomiting) occurred at 70 mg/m2, and the MTD was not reached. The most common ≥ grade 3 TEAEs related to HE072 included neutropenia (21.0%), leukopenia (18.5%), diarrhea (10.1%). Among 87 evaluable patients with mTNBC, 22 patients (25.3%) achieved overall response. The DCR was 67.8% (59/87). The median PFS and OS were 4.8 months and 14.1 months, respectively. The RP2D was 70 mg/m2 Q2W. Promising antitumor activity in heavily pre-treated patients with mTNBC was observed, which warrants further validation.

Survival Among Patients With ERBB2-Positive Metastatic Breast Cancer and Central Nervous System Disease

Importance

Approximately one-third of patients with ERBB2 (formerly HER2 or HER2/neu)-positive (ERBB2+) metastatic breast cancer (MBC) develop brain metastasis. It is unclear whether patients with disease limited to the central nervous system (CNS) have different outcomes and causes of death compared with those with concomitant extracranial metastasis.

Objective

To assess overall survival (OS) and CNS-related mortality among patients with ERBB2+ breast cancer and a diagnosis of CNS disease by disease distribution (CNS only vs CNS plus extracranial metastasis).

Design, Setting, and Participants

This single-center, retrospective cohort study included patients with ERBB2+ MBC and CNS disease, including parenchymal brain metastasis, leptomeningeal disease (LMD), or dural metastasis, who were treated between August 2010 and April 2022 at Memorial Sloan Kettering Cancer Center. Data were analyzed between December 2023 and August 2024.

Main Outcomes and Measures

Overall survival, estimated with the Kaplan-Meier method, and CNS-related mortality with cumulative incidence.

Results

The cohort included 274 patients (272 [99.3%] female). The median age was 53.7 years (range, 28.7-87.4 years); 125 patients (45.6%) presented with de novo MBC. At CNS metastasis diagnosis, 73 (26.6%) presented with CNS-only disease. There was a median follow-up of 3.7 years (range, 0.2-12.0 years) from CNS disease diagnosis among those alive at the end of follow-up. Both OS and CNS-related death were significantly correlated with the pattern of presentation: OS was shortest among patients with LMD (1.24 years; 95% CI, 0.89-2.08 years) followed by those with extracranial metastasis (2.16 years; 95% CI, 1.87-2.58 years) and was longest among patients with parenchymal or dural CNS disease only (3.57 years; 95% CI, 2.10-5.63 years) (P = .001). Of 192 patients (70.1%) who died, 106 (55.2%) died of a CNS-related cause. The group with CNS-only disease remained at high risk of death from CNS causes, with a 3-year CNS-related death rate of 33.98% (95% CI, 22.84%-45.43%) and a 3-year death rate from other causes of 6.07% (95% CI, 1.93%-13.69%). On multivariable modeling for CNS-related death, LMD (hazard ratio, 1.87; 95% CI, 1.19-2.93; P = .007) and treatment with whole-brain radiotherapy (hazard ratio, 1.71; 95% CI, 1.13-2.58; P = .01) were associated with CNS-related death.

Conclusions and Relevance

In this cohort study, 55.2% of deaths among patients with ERBB2+ breast cancer and brain metastasis were due to CNS-related causes, with the greatest risk among patients with LMD. CNS-only presentation was associated with improved survival but a higher rate of CNS-related death, supporting an approach of aggressive local therapy for select patients.

Expert consensus on the prevention of brain metastases in patients with HER2-positive breast cancer

BACKGROUND

Patients with HER2-positive breast cancer have a significant risk of developing brain metastases (BrM), which have detrimental effects on survival outcomes and quality of life. Although there are several systemic treatment options available that may delay the appearance of BrM and secondary progression of previously treated BrM, there are still substantial unmet needs for this patient population and primary prevention remains elusive.

METHODS

A group of experts created consensus statements, through a modified Delphi process, to bridge the gap between current unmet needs, available evidence, and international guidelines.

RESULTS

The steering committee reviewed all relevant literature and formed research questions to be answered by the subsequent consensus statements. In total, 61 contributors provided feedback on the consensus statements, with 34 statements reaching agreement out of the 55 statements that were voted on altogether. Statements with consensus aimed to define BrM primary and secondary prevention, screening procedures, assessment of symptoms, treatment efficacy, and preventing the occurrence and progression of BrM, while acknowledging the possibilities and limitations in daily clinical practice. Some statements did not reach agreement for a variety of reasons, mostly due to lack of evidence.

CONCLUSIONS

The consensus statements outlined in this publication provide a point of reference for daily clinical practice and can act as recommendations for clinical trial procedures and future guidelines.

Intracranial outcomes following neurosurgical resection in patients with brain metastases secondary to HER2-positive breast cancer versus other subtypes

PURPOSE

Neurosurgical resection serves an important role in select patients with breast cancer and brain metastases but can delay systemic therapy and yield complications. Consequently, identification of patients most likely to benefit from surgery is important. Given the poorer long-term intracranial responses to radiotherapy sometimes observed in HER2-positive (HER2 +) patients, we investigated whether neurosurgical resection is differentially beneficial in this population.

METHODS

We identified 633 patients with newly diagnosed brain metastases arising from breast cancer managed at Brigham and Women's Hospital/Dana-Farber Cancer Institute between 2010 and 2022. Patients were stratified by breast cancer subtype: HER2 + (N = 189), hormone receptor positive (HR +)/HER2- (N = 267), and triple negative (N = 177). Per-patient and per-metastasis outcomes were evaluated; interaction models assessing the impact of neurosurgical resection by subtype were constructed.

RESULTS

Relative to HR + /HER2- subtype, omission of upfront neurosurgical resection in patients with HER2 + disease was associated with increased subsequent utilization of salvage stereotactic radiation, whole brain radiotherapy, and craniotomy (interaction HR 2.02 [95% CI, 1.04-3.93], p = 0.04; HR 3.92 [95% CI, 1.24-12.40], p = 0.02; HR 4.98 [95% CI, 1.34-18.58], p = 0.02, respectively). Tumors stemming from HER2 + versus HR + /HER2- primaries displayed increased local recurrence when upfront neurosurgical resection was omitted (interaction HR 3.62 [95% CI, 1.06-12.38], p = 0.04). No such associations were noted when comparing triple negative to HR + /HER2- subtype (p-interaction > 0.05 in all cases).

CONCLUSION

Patients with HER2 + disease and brain metastases may disproportionately benefit from upfront neurosurgical resection relative to other subtypes. If validated, our results may suggest a lower threshold to consider surgery in brain metastases secondary to HER2 + breast cancer.

Microenvironmental Regulation of Dormancy in Breast Cancer Metastasis: "An Ally that Changes Allegiances"

Breast cancer remission after treatment is sometimes long-lasting, but in about 30% of cases, there is a relapse after a so-called dormant state. Cellular cancer dormancy, the propensity of disseminated tumor cells (DTCs) to remain in a nonproliferative state for an extended period, presents an opportunity for therapeutic intervention that may prevent reawakening and the lethal consequences of metastatic outgrowth. Therefore, identification of dormant DTCs and detailed characterization of cancer cell-intrinsic and niche-specific [i.e., tumor microenvironment (TME) mediated] mechanisms influencing dormancy in different metastatic organs are of great importance in breast cancer. Several microenvironmental drivers of DTC dormancy in metastatic organs, such as the lung, bone, liver, and brain, have been identified using in vivo models and/or in vitro three-dimensional culture systems. TME induction and persistence of dormancy in these organs are mainly mediated by signals from immune cells, stromal cells, and extracellular matrix components of the TME. Alterations of the TME have been shown to reawaken dormant DTCs. Efforts to capitalize on these findings often face translational challenges due to limited availability of representative patient samples and difficulty in designing dormancy-targeting clinical trials. In this chapter, we discuss current approaches to identify dormant DTCs and provide insights into cell-extrinsic (i.e., TME) mechanisms driving breast cancer cell dormancy in distant organs.

Metastatic brain tumors: from development to cutting-edge treatment

Metastatic brain tumors, also called brain metastasis (BM), represent a challenging complication of advanced tumors. Tumors that commonly metastasize to the brain include lung cancer and breast cancer. In recent years, the prognosis for BM patients has improved, and significant advancements have been made in both clinical and preclinical research. This review focuses on BM originating from lung cancer and breast cancer. We briefly overview the history and epidemiology of BM, as well as the current diagnostic and treatment paradigms. Additionally, we summarize multiomics evidence on the mechanisms of tumor occurrence and development in the era of artificial intelligence and discuss the role of the tumor microenvironment. Preclinically, we introduce the establishment of BM models, detailed molecular mechanisms, and cutting-edge treatment methods. BM is primarily treated with a comprehensive approach, including local treatments such as surgery and radiotherapy. For lung cancer, targeted therapy and immunotherapy have shown efficacy, while in breast cancer, monoclonal antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates are effective in BM. Multiomics approaches assist in clinical diagnosis and treatment, revealing the complex mechanisms of BM. Moreover, preclinical agents often need to cross the blood-brain barrier to achieve high intracranial concentrations, including small-molecule inhibitors, nanoparticles, and peptide drugs. Addressing BM is imperative.

Targeting HER2 in breast cancer with brain metastases: A pharmacological point of view with special focus on the permeability of blood-brain barrier to targeted treatments

Understanding the capability of a drug to penetrate the blood-brain barrier (BBB) is an unmet medical need in patients with positive human epidermal growth factor receptor 2 (HER2 positive) and brain metastases. The National Comprehensive Cancer Network (NCCN) guidelines recommend the use of tyrosine kinase inhibitors (TKIs) lapatinib, neratinib, and tucatinib in co-administration with monoclonal antibodies or chemotherapy drugs and the antibody-drug conjugates (ADCs) trastuzumab-deruxtecan and trastuzumab-emtansine. Predicting the BBB permeability of these therapeutic agents is a pharmacological challenge due to the various factors involved in the barrier functions. In this review article, we discuss about the molecular and cellular features of the barriers located in the central nervous system and the pharmacological parameters found to be important in predicting BBB permeability in human normal brain, and in the presence of brain metastases. Finally, we reported the clinical outcomes and intracranial response of patients with HER2-positive breast cancer with brain metastases treated with targeted TKIs and ADCs.

Current Evidence in the Systemic Treatment of Brain Metastases from Breast Cancer and Future Perspectives on New Drugs, Combinations and Administration Routes: A Narrative Review

Breast cancer is the most frequently diagnosed neoplasm all over the world and the second leading cause of cancer death in women. Breast cancer prognosis has significantly improved in the last years due to the advent of novel therapeutic options, both in the early and in advanced stages. However, the spread of the disease to the brain, accounting for 15-30% of the metastatic diagnoses, is challenging, and its poor prognosis represents an unmet medical need, leading to deterioration of quality of life and causing morbidity and mortality. Generally, triple-negative and HER2-positive breast cancer subtypes more frequently spread to the brain or in the leptomeningeal space. Consequently, according to international guidelines, several systemic treatments can be offered as a first option in some subsets of patients. However, a multidisciplinary approach is recommended to offer the most appropriate strategy to patients. Antibody-drug conjugates such as trastuzumab deruxtecan or sacituzumab govitecan along with small molecules have led to important achievements in the treatment of brain metastases from HER2-positive and triple-negative breast cancer. In this narrative review, we will focus on the molecular features leading to the development of brain metastases and explore the risk and the prognostic factors involved in the development of brain metastases. Finally, we will review the major achievements in the treatment landscape of brain metastases from breast cancer and novel medical approaches.

BMScope: A scoping review to chart the evolving clinical study landscape in brain and leptomeningeal metastasis

BACKGROUND

Recent studies have challenged the notion that patients with brain metastasis (BM) or leptomeningeal metastasis (LM) should be excluded from systemic therapy clinical trials. This scoping study summarizes the BM/LM clinical studies published between 2010 and 2023.

METHODS

MEDLINE, CINAHL, CAB Abstracts, PsycINFO, Cochrane Library, HINARI, International Pharmaceutical Abstracts, PubMed, Scopus, Web of Science, and EMBASE electronic databases were searched on June 21, 2021. An updated search was performed on February 21, 2023. Eligible studies investigated a therapeutic intervention in solid tumor patients with BM and/or LM and reported a patient outcome. Extracted study-level data, including study type, publication date, geographical location, number of BM/LM patients in the study, primary tumor type, and type of therapeutic intervention, were collected.

RESULTS

4921 unique studies were eligible for analysis. The key finding is that BM/LM clinical research is expanding globally, both in observational studies and clinical trials. Despite the shift over time toward a higher proportion of systemic therapy trials, the majority still do not include patients with symptomatic disease and lack reporting of BM/LM-specific endpoints. Globally, there has been a trend to more international collaboration in BM/LM clinical studies.

CONCLUSIONS

Our analysis of the BM/LM literature charts the evolving landscape of studies involving this previously excluded population. Given the increasing clinical research activity, particularly involving late-stage systemic therapy trials, it is imperative that due consideration is given to the intracranial activity of new investigational agents. Wider adoption of standardized reporting of intracranial-specific endpoints will facilitate the evaluation of relative intracranial efficacy.

A pooled analysis of trastuzumab deruxtecan in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer with brain metastases

BACKGROUND

This exploratory pooled analysis investigated the efficacy and safety of trastuzumab deruxtecan (T-DXd) versus comparator treatment in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) with brain metastases (BMs) at baseline, categorized according to previous local treatment.

PATIENTS AND METHODS

T-DXd data were pooled from DESTINY-Breast01/-02/-03. Comparator data, from patients receiving physician's choice therapy and trastuzumab emtansine, were pooled from DESTINY-Breast02 and -03, respectively. Baseline BM status was assessed according to US Food and Drug Administration criteria. The endpoints included intracranial objective response rate (ORR; complete or partial response in the brain) per blinded independent central review (BICR) by RECIST version 1.1, time to intracranial response, intracranial duration of response (DoR), central nervous system progression-free survival (CNS-PFS) by BICR, overall survival (OS), and safety.

RESULTS

A total of 148 patients who received T-DXd and 83 patients who received comparator treatment had BMs at baseline. In those treated with T-DXd, the intracranial ORR of patients with treated/stable and untreated/active BMs was 45.2% and 45.5%, respectively. The median (range) time to intracranial response was 2.8 months (1.1-13.9 months) and 1.5 months (1.2-13.7 months) in patients with treated/stable and untreated/active BMs, respectively. For those with treated/stable BMs, the median intracranial DoR was 12.3 [95% confidence interval (CI) 9.1-17.9] months, and for those with untreated/active BMs, it was 17.5 months (95% CI 13.6-31.6 months). The median CNS-PFS and OS were 12.3 months (95% CI 11.1-13.8 months) and not reached (95% CI 22.1 months-not estimable) in those with treated/stable BMs, and 18.5 months (95% CI 13.6-23.3 months) and 30.2 months (95% CI 21.3 months-not estimable) in those with untreated/active BMs, respectively. Drug-related treatment-emergent adverse events grade ≥3 were experienced by 43.2% of patients with BMs and 46.4% without BMs with T-DXd.

CONCLUSIONS

T-DXd demonstrated meaningful intracranial efficacy and clinical benefit in OS, with an acceptable and manageable safety profile in patients with HER2-positive mBC with treated/stable and untreated/active BMs.

Identification of Tumor-Suppressive miR-30a-3p Controlled Genes: ANLN as a Therapeutic Target in Breast Cancer

Our recently created RNA-sequence-based microRNA (miRNA) expression signature in breast cancer clinical specimens revealed that some miR-30 family members were significantly downregulated in cancer tissues. Based on TCGA database analyses, we observed that among the miR-30 family members, miR-30a-3p (the passenger strand derived from pre-miR-30a) was significantly downregulated in breast cancer (BC) clinical specimens, and its low expression predicted worse prognoses. Ectopic expression assays showed that miR-30a-3p transfected cancer cells (MDA-MB-157 and MDA-MB-231) had their aggressive phenotypes significantly suppressed, e.g., their proliferation, migration, and invasion abilities. These data indicated that miR-30a-3p acted as a tumor-suppressive miRNA in BC cells. Our subsequent search for miR-30a-3p controlled molecular networks in BC cells yielded a total of 189 genes. Notably, among those 189 genes, cell-cycle-related genes (ANLN, MKI67, CCNB1, NCAPG, ZWINT, E2F7, PDS5A, RIF1, BIRC5, MAD2L1, CACUL1, KIF23, UBE2S, EML4, SEPT10, CLTC, and PCNP) were enriched according to a GeneCodis 4 database analysis. Moreover, the overexpression of four genes (ANLN, CCNB1, BIRC5, and KIF23) significantly predicted worse prognoses for patients with BC according to TCGA analyses. Finally, our assays demonstrated that the overexpression of ANLN had cancer-promoting functions in BC cells. The involvement of miR-30a-3p (the passenger strand) in BC molecular pathogenesis is a new concept in cancer research, and the outcomes of our study strongly indicate the importance of analyzing passenger strands of miRNAs in BC cells.

Multi-institutional report of trastuzumab deruxtecan and stereotactic radiosurgery for HER2 positive and HER2-low breast cancer brain metastases

Trastuzumab-deruxtecan (T-DXd) has demonstrated intracranial efficacy; however, safety and efficacy data remains limited with stereotactic radiosurgery (SRS). A multi-institutional review was performed with HER2+ or HER2-low metastatic breast cancer treated with T-DXd and SRS for active brain metastases. We identified 215 lesions treated over 48 SRS courses in 34 patients. Median follow up from T-DXd initiation was 13.9 months. The cumulative incidence of symptomatic radiation necrosis at 24 months per lesion was 2.1% and per patient 11%. The 12-month LC was 97%. HER2-low was associated with worse distant intracranial control (DIC) (adjusted HR 2.5, 95% CI 1.1-5.6, p = 0.03) and worse systemic progression free survival (PFS) (HR 4.1, 95% CI 1.6-10.7, p = 0.004). Concurrent SRS and T-DXd has excellent local control, without an increased risk of radiation necrosis. HER2-low disease is associated with worse systemic PFS and DIC with T-DXd compared to HER2+.

Guidance for Canadian Breast Cancer Practice: National Consensus Recommendations for Clinical Staging of Patients Newly Diagnosed with Breast Cancer

The accurate staging of breast cancer is fundamental for guiding treatment decisions and predicting patient outcomes. However, there can be considerable variation in routine clinical practice based on individual interpretation of guidelines and depending on the healthcare provider initially involved in working up patients newly diagnosed with breast cancer, ranging from primary care providers, triage nurses, surgeons, and/or oncologists. The optimal approach for clinical staging, particularly in asymptomatic patients presenting with intermediate-risk disease, remains a topic of dialogue among clinicians. Given this area of uncertainty, the Research Excellence, Active Leadership (REAL) Canadian Breast Cancer Alliance conducted a modified Delphi process to assess the level of agreement among Canadian expert clinicians on various staging recommendations. In total, 20 items were drafted covering staging based on biological status, the utilization of localization clips, both for the axilla during diagnosis and primary surgical site for margins and radiation therapy planning, and the use of advanced imaging for the investigation of distant metastases. Overall, the consensus threshold among all participants (i.e., ≥75% agreement) was reached in 20/20 items. Differences in clinical practice and recent findings from the literature are provided in the discussion. These consensus recommendations are meant to help standardize breast cancer staging practices in Canada, ensuring accurate diagnosis and optimal treatment planning.

Optimizing Drug Delivery to the Brain for Breast Metastasis: A Novel Method for Tumor Targeting

INTRODUCTION

Brain metastases are difficult to treat due to the blood-brain barrier limiting the delivery of therapeutic agents to the brain effectively. Intraventricular drug delivery has not been well studied for intra-axial pathologies. However, our prior work demonstrated that intraventricular drug delivery in a hyperosmolar vehicle showed preferential accumulation of drug within breast cancer tissue compared to surrounding brain parenchyma. The focus of this study was to explore the molecular parameters of intraventricular drug administration that may optimize drug delivery to intra-axial brain metastases. Our hypothesis was that a low molecular weight drug with a high osmolarity solution would increase drug delivery to tumor tissue.

METHODS

We used an intracerebral breast cancer tumor model in adult female nude rats divided into six experimental groups. We examined three iron-labeled dextran molecules (3 kD, 5 kD, and 10 kD) in 337 mOsm/L solution and three different osmolarities of delivery solution (307, 353, and 368 mOsm/L) with 10 kD dextran. 7T magnetic resonance imaging (MRI) was used to analyze dextran distribution at different time points. All animals were sacrificed after two hours, and the quantity of dextran particles was determined by histopathology.

RESULTS

Breast cancer tumor cells were successfully implanted in all rats. The MRI quantification of dextran concentration was well corroborated by histopathology. Varying the molecular size of dextran resulted in the smallest molecule reaching peak levels in tumor tissue earlier than the larger molecules, but the larger molecules remained concentrated in tumor tissue for a longer time. Varying the osmolarity of the delivery solution resulted in the preferential accumulation of 10 kD dextran in tumor tissue except for when dextran was delivered in 368 mOsm/L solution where no preferential distribution was seen.

CONCLUSION

Hyperosmolar intraventricular delivery of chemotherapeutic drugs could be effective in preferentially delivering drugs to abnormal tumor tissues.

Trastuzumab deruxtecan for the treatment of patients with HER2-positive breast cancer with brain and/or leptomeningeal metastases: an updated overall survival analysis using data from a multicenter retrospective study (ROSET-BM)

We provide updated results (median follow-up duration: 20.4 months) of a retrospective study on the effectiveness of trastuzumab deruxtecan (T-DXd) in patients with human epidermal growth factor receptor 2-positive (HER2+) breast cancer with brain metastases (BM) and/or leptomeningeal disease (ROSET-BM). Median progression-free survival (PFS) was 14.6 months. Median overall survival (OS) was not reached (NR); 24-month OS rate was 56.0%. Subgroup analysis showed that median PFS was 13.2 months in patients with analytical active BM, 17.5 months in patients with leptomeningeal carcinomatosis (LMC), and NR in patients with analytical stable BM (24-month PFS rates in patients with analytical active BM, LMC, and analytical stable BM were 32.7%, 25.1%, and 60.8%, respectively). Median OS was 27.0 months in patients with analytical active BM and NR in patients with LMC or analytical stable BM (24-month OS rates in patients with analytical active BM, LMC, and analytical stable BM were 52.0%, 61.6%, and 71.6%, respectively). The most common adverse event leading to discontinuation of T-DXd was interstitial lung disease (ILD; 23.1%); median ILD onset time among patients who discontinued T-DXd treatment due to ILD was 5.3 months. T-DXd has promising effectiveness in heavily pre-treated HER2+ metastatic breast cancer patients with BM and LMC. The incidence and median onset time of ILD were similar to those of Japanese subgroups in previous studies.

Invasive disease-free survival and brain metastasis rates in patients treated with neoadjuvant chemotherapy with trastuzumab and pertuzumab

Patients with HER2(+) early breast cancer (EBC) receiving neoadjuvant systemic therapy (NAST) have poorer outcomes if they have residual disease (RD). We analyzed IDFS and brain metastasis (BM) rates in patients with HER2(+) EBC treated with NAST and report the outcomes of patients with HER2(-) RD. Patients with HER2(+) EBC who received NAST between 1 Jan 2019 and 31 Jan 2022 were reviewed. IDFS was defined as the time from surgery until first occurrence of invasive breast cancer recurrence, distant recurrence, or death from any cause. The total cohort was 594 patients. pCR (ypT0/isN0) was achieved in 325(55%) and RD was seen in 269(45%) patients. In 269 patients with RD, 45(17%) did not have HER2 retesting and were excluded. In the remaining 224 patients, 143(64%) were HER2(+) and 81(36%) were HER2(-). With a median follow up of 24 months, 8 patients developed BM at initial recurrence, 4/325(1.2%) with pCR and 4/143(2.8%) with HER2(+) RD. IDFS events occurred in 22/594(3%) patients; 14/269(5%) in RD and 8/325(2%) in pCR (p = 0.04). There was no difference in IDFS between 9/143(6%) patients with HER2(+) RD or 5/81(6%) with HER2(-) RD (p = 0.10). Patients with RD had higher IDFS events than those with pCR. In those with RD, 36% lost HER2(+) status; IDFS events appeared similar in those with HER2(+) RD versus those with HER2(-) RD. The BM events seen in those with RD and pCR highlights the need for more effective therapy in NAST and adjuvant setting to minimize BM risk.

Guidance for Canadian Breast Cancer Practice: National Consensus Recommendations for the Systemic Treatment of Patients with HER2+ Breast Cancer in Both the Early and Metastatic Setting

Human epidermal growth factor receptor 2-positive (HER2+) breast cancer is an aggressive subtype of breast cancer associated with a poor prognosis when sub-optimally treated. Recent advances include new and effective targeted therapies that have significantly improved outcomes for patients. Despite these advances, there are significant gaps across Canada, underscoring the need for evidence-based consensus guidance to inform treatment decisions. Addressing these gaps is crucial to ensuring that effective therapies are integrated into clinical practice, so as to improve the lives of patients affected by this aggressive form of breast cancer. The Research Excellence, Active Leadership (REAL) Canadian Breast Cancer Alliance is a standing nucleus committee of clinical-academic oncologists across Canada and Breast Cancer Canada, a patient organization. The mandate of this group is to provide evidence-based guidance on best practices in the management of patients with breast cancer. These consensus recommendations were developed using a modified Delphi process with up to three rounds of anonymous voting. Consensus was defined a priori as ≥75% of voters agreeing with the recommendation as written. There are 9 recommendations in the early setting; 7 recommendations in the metastatic setting; and 10 recommendations for patients with brain metastases.

Real-world outcomes in patients with brain metastases secondary to HR+/HER2- MBC treated with abemaciclib and local intracranial therapy

BACKGROUND

Real-world data are limited for patients with brain metastases secondary to metastatic breast cancer (MBC) and treated with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i). This study describes real-world outcomes in patients with hormone receptor-positive, human epidermal growth factor 2-negative (HR+/HER2-) MBC with brain metastases diagnosis before abemaciclib initiation.

PATIENTS AND METHODS

A nationwide electronic health record-derived de-identified MBC database (January 2011-December 2021) was assessed retrospectively. Patients with HR+/HER2- MBC who were treated with abemaciclib (monotherapy or in combination) following diagnosis of brain metastases were included. Real-world best response reflected clinician-documented response assessment of the brain imaging (intracranial) and change in disease burden following radiographic imaging (extracranial); these were reported descriptively. Time to treatment discontinuation (TTD), real-world progression-free survival (rwPFS), and overall survival (rwOS) were assessed using Kaplan-Meier methods from abemaciclib initiation (index date).

RESULTS

Among 82 included patients (mean age 57.0 years; 98.8% female), 22.0% and 19.5% received CDK4/6i and chemotherapy before abemaciclib initiation, respectively, and the majority (80.5%) received radiation/local surgery to the brain before abemaciclib initiation. Patients mostly received abemaciclib as monotherapy (n = 6) or in combination with endocrine therapy (n = 68). Median TTD was 7.1 (95% CI 4.6-11.3) months, rwPFS was 9.2 (95% CI 6.0-11.6) months, and rwOS was 20.8 (95% CI 13.9-26.0) months. Intracranial and extracranial objective response rates, as determined by treating physicians, were 45.1% (n = 23/51) and 56.7% (n = 34/60), respectively. Intracranial and extracranial clinical benefit rates were 62.7% (n = 32/51) and 70.0% (n = 42/60), respectively.

CONCLUSION

In this real-world study of patients diagnosed with brain metastases and initiating abemaciclib, most patients received radiation/local surgery to the brain before abemaciclib initiation. Although the outcomes in this real-world study are encouraging, it is unclear if the benefit was due to local therapy, abemaciclib, or the combination, and causality cannot be inferred. Further prospective clinical studies are needed to confirm the clinical benefit of this approach.

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.

Stereotactic radiosurgery for brain metastases from human epidermal receptor 2 positive breast Cancer: an international, multi-center study

PURPOSE

To report patient outcomes and local tumor control rates in a cohort of patients with biopsy-proven HER-2 positive breast cancer treated with stereotactic radiosurgery (SRS) for brain metastases (BM).

METHODS

This international, retrospective, multicenter study, included 195 female patients with 1706 SRS-treated BM. Radiologic and clinical outcomes after SRS were determined and prognostic factors identified.

RESULTS

At SRS, median patient age was 55 years [interquartile range (IQR) 47.6-62.0], and 156 (80%) patients had KPS ≥ 80. The median tumor volume was 0.1 cm3 (IQR 0.1-0.5) and the median prescription dose was 16 Gy (IQR 16-18). Local tumor control (LTC) rate was 98%, 94%, 93%, 90%, and 88% at six-, 12-, 24-, 36- and 60-months post-SRS, respectively. On multivariate analysis, tumor volume (p = < 0.001) and concurrent pertuzumab (p = 0.02) improved LTC. Overall survival (OS) rates at six-, 12-, 24-, 36-, 48-, and 60-months were 90%, 69%, 46%, 27%, 22%, and 18%, respectively. Concurrent pertuzumab improved OS (p = 0.032). In this patient subgroup, GPA scores ≥ 2.5 (p = 0.038 and p = 0.003) and rare primary tumor histologies (p = 0.01) were associated with increased and decreased OS, respectively. Asymptomatic adverse radiation events (ARE) occurred in 27 (14.0%) and symptomatic ARE in five (2.6%) patients. Invasive lobular carcinoma primary (p = 0.042) and concurrent pertuzumab (p < 0.001) conferred an increased risk for overall but not for symptomatic ARE.

CONCLUSION

SRS affords effective LTC for selected patients with BM from HER-2 positive breast cancer. Concurrent pertuzumab improved LTC and OS but at the same time increased the risk for overall, but not symptomatic, ARE.

Trastuzumab deruxtecan in patients with previously treated HER2-low advanced breast cancer and active brain metastases: the DEBBRAH trial

BACKGROUND

Trastuzumab deruxtecan (T-DXd) is approved for human epidermal growth factor receptor 2 (HER2)-positive and HER2-low advanced breast cancer (ABC). T-DXd has shown encouraging intracranial activity in HER2-positive ABC patients with stable or active brain metastases (BMs); however, its efficacy in patients with HER2-low ABC with BMs is not well established yet.

METHODS

DEBBRAH is a single-arm, five-cohort, phase II study evaluating T-DXd in patients with central nervous system involvement from HER2-positive and HER2-low ABC. Here, we report results from patients with heavily pretreated HER2-low ABC and active BMs, enrolled in cohorts 2 (n = 6, asymptomatic untreated BMs) and 4 (n = 6, progressing BMs after local therapy). Patients received 5.4 mg/kg T-DXd intravenously once every 21 days. The primary endpoint was intracranial objective response rate per Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) for both cohorts.

RESULTS

Intracranial objective response rate per RANO-BM was 50.0% [3/6 patients; 95% confidence interval (CI) 11.8% to 88.2%] and 33.3% [2/6 patients; 95% CI 4.3% to 77.7%; P = 0.033 (one-sided)] in cohorts 2 and 4, respectively. All responders had partial responses. Median time to intracranial response was 2.3 months (range, 1.5-4.0 months) and median duration of intracranial response was 7.2 months (range, 2.8-16.8 months). Median progression-free survival per RECIST v.1.1. was 5.4 months (95% CI 4.1-10.0 months). Treatment-emergent adverse events occurred in all patients included (16.7% grade 3). Three patients (25.0%) had grade 1 interstitial lung disease/pneumonitis.

CONCLUSIONS

T-DXd demonstrated promising intracranial activity in pretreated HER2-low ABC patients with active BMs. Further studies are needed to validate these results in larger cohorts. This trial is registered with ClinicalTrials.gov, NCT04420598.

Multifaceted interactions between cancer cells and glial cells in brain metastasis

Cancer brain metastasis has a poor prognosis, is commonly observed in clinical practice, and the number of cases is increasing as overall cancer survival improves. However, experiments in mouse models have shown that brain metastasis itself is an inefficient process. One reason for this inefficiency is the brain microenvironment, which differs significantly from that of other organs, making it difficult for cancer cells to adapt. The brain microenvironment consists of unique resident cell types such as neurons, oligodendrocytes, astrocytes, and microglia. Accumulating evidence over the past decades suggests that the interactions between cancer cells and glial cells can positively or negatively influence the development of brain metastasis. Nevertheless, elucidating the complex interactions between cancer cells and glial cells remains challenging, in part due to the limitations of existing experimental models for glial cell culture. In this review, we first provide an overview of glial cell culture methods and then examine recent discoveries regarding the interactions between brain metastatic cancer cells and the surrounding glial cells, with a special focus on astrocytes and microglia. Finally, we discuss future perspectives for understanding the multifaceted interactions between cancer cells and glial cells for the treatment of metastatic brain tumors.

Proteomic insights into breast cancer response to brain cell-secreted factors

The most devastating feature of cancer cells is their ability to metastasize to distant sites in the body. HER2 + and TN breast cancers frequently metastasize to the brain and stay potentially dormant for years until favorable conditions support their proliferation. The sheltered and delicate nature of the brain prevents, however, early disease detection and effective delivery of therapeutic drugs. Moreover, the challenges associated with the acquisition of brain biopsies add compounding difficulties to exploring the mechanistic aspects of tumor development. To provide insights into the determinants of cancer cell behavior at the brain metastatic site, this study was aimed at exploring the early response of HER2 + breast cancer cells (SKBR3) to factors present in the brain perivascular niche. The neural microenvironment was simulated by using the secretome of a set of brain cells that come first in contact with the cancer cells upon crossing the blood brain barrier, i.e., endothelial cells, astrocytes, and microglia. Cytokine microarrays were used to investigate the secretome mediators of intercellular communication, and proteomic technologies for assessing the changes in the behavior of cancer cells upon exposure to the brain cell-secreted factors. The cytokines detected in the brain secretomes were supportive of inflammatory conditions, while the SKBR3 cells secreted numerous cancer-promoting growth factors that were either absent or present in lower abundance in the brain cell cultures, indicating that upon exposure the SKBR3 cells may have been deprived of favorable conditions for optimal growth. Altogether, the results suggest that the exposure of SKBR3 cells to the brain cell-secreted factors altered their growth potential and drove them toward a state of quiescence, with broader overall outcomes that affected cellular metabolism, adhesion and immune response processes. The findings of this study underscore the key role played by the neural niche in shaping the behavior of metastasized cancer cells, provide insights into the cellular cross-talk that may lead cancer cells into dormancy, and highlight novel opportunities for the development of metastatic breast cancer therapeutic strategies.

Crosstalk between breast cancer-derived microRNAs and brain microenvironmental cells in breast cancer brain metastasis

Breast cancer is the most frequent malignancy in women, constituting 15.2% of all new cancers diagnosed in the United States. Distant breast cancer metastasis accounts for the majority of breast cancer-related deaths; brain metastasis is the third most common site for metastatic breast cancer but is associated with worst prognosis of approximately eight months of survival. Current treatment options for breast cancer brain metastasis (BCBM) are limited and ineffective. To help identify new and effective therapies for BCBM, it is important to investigate the mechanisms by which breast cancer cells metastasize to the brain and thrive in the brain microenvironment. To this end, studies have reported that primary breast tumor cells can prime brain microenvironmental cells, including, astrocytes and microglia, to promote the formation of BCBM through the release of extracellular vesicle-microRNAs (miRNAs). Breast tumor-derived miRNAs can also promote breast cancer cell invasion through the blood-brain barrier by disrupting the integrity of the brain microvascular endothelial cells. In this review, we summarize current literature on breast cancer-derived BCBM-promoting miRNAs, cover their roles in the complex steps of BCBM particularly their interactions with microenvironmental cells within the brain metastatic niche, and finally discuss their therapeutic applications in the management of BCBM.

Clinico-pathologic factors and survival of patients with breast cancer diagnosed with de novo brain metastasis: a national cancer database analysis

PURPOSE

Patients with Breast Cancer (BC) with Brain Metastasis (BCBM) have poor survival outcomes. We aimed to explore the clinico-pathologic and therapeutic factors predicting the survival in patients with de novo BCBM using the National Cancer Database (NCDB).

PATIENTS AND METHODS

The NCDB was queried for patients with BC between 2010 and 2020. Survival analysis with Kaplan-Meier curves and log rank tests were used to find median overall survival (OS) in months (95% CI) across the different variables. A multivariate cox regression model was computed to identify significant predictors of survival.

RESULTS

Out of n = 2,610,598 patients, n = 9005 (0.34%) had de novo BCBM. A trend of decreasing OS was observed with increasing age, Charlson-Deyo score (CDS), and number of extracranial metastatic sites. The highest median OS was observed in the Triple Positive and the lowest OS in the Triple Negative subgroup. Based on treatment regimen, combination of systemic therapy and local therapy achieved the highest OS. A positive trend in OS was observed in the BC subgroup analysis with targeted therapy demonstrating a survival benefit when added to systemic therapy. The multivariate cox regression model showed that age, race, ethnicity, insurance, median income, facility type, CDS, BC subtype, metastatic location sites, and treatment combinations received were significantly associated with risk of death. Receiving only local treatment for BM without systemic therapy more than doubled the risk of death compared to combining it with systemic therapy.

CONCLUSIONS

This analysis suggests that treatment of systemic disease is the major factor influencing survival in patients with BCBM. Moreover, targeted therapy with anti-HER2 increased survival when added to systemic therapy explaining the highest median OS noted in the Triple Positive subgroup.

The incidence of brain metastases in breast cancer according to molecular subtype and stage: a 10-year single institution analysis

BACKGROUND

Breast cancer (BC) is the second most common etiology of brain metastases (BrM). We aimed to examine the incidence of BrM among all BC patients presenting to a large tertiary cancer centre over one decade.

METHODS

We included all BC patients presenting consecutively between 2009 and 2019 and cross referenced that cohort to a radiotherapy database, identifying patients treated for BrM at any time following their initial presentation. Cumulative incidences (CI) of BrM diagnoses were calculated using death as a competing risk and compared using the Fine-Gray method. Overall survival was estimated using the Kaplan Meier method.

RESULTS

We identified 12,995 unique patients. The CI of BrM in patients who initially presented with Stage 0-4 disease was 2.1%, 3.7%, 9.4%, 10.6%, and 28.7%, respectively at 10 years. For 8,951 patients with available molecular subtype data, 6,470 (72%), 961 (11%), 1,023 (11%), and 497 (6%) had hormone-receptor (HR)-positive/ERBB2-, HR-negative/ERBB2-, HR-positive/ERBB2 + , and HR-negative/ERBB2 + disease, respectively; the CI of BrM in each was 7.6%, 25.3%, 24.1%, and 26.6%, at 10 years following BC diagnosis, respectively. Median overall survival (OS) following BC diagnosis and BrM diagnosis was 28 years 95% CI [25, 32] and 10 months 95% CI [9, 12], respectively.

CONCLUSIONS

From a large, registry-based study, we observed that patients with ERBB2 + and triple negative BC have the highest incidence of BrM. Our data supports prospective surveillance brain MRI studies. Given advancements in BrM treatment, clinicians should have a low threshold for brain imaging in BC patients with high risk subtypes.

Impact of cyclin dependent kinase 4/6 inhibitors on breast cancer brain metastasis outcomes

BACKGROUND

Cyclin dependent kinase 4/6 inhibitors (CDK4/6i) are recommended 1st line treatments in HR+HER2- metastatic breast cancer. However, the impact of prior CDK4/6i on the natural history of brain metastases (BM) is not well described.

MATERIALS AND METHODS

We reviewed retrospective data for 363 patients with HR+HER2- BM who received a CDK4/6i (CDK-Y) between 1 Jan 2015 to 31 July 2021 and 299 patients with HR+HER2- BM who did not receive a CDK4/6i (CDK-N) between 1 Jan 2010 to 31 Dec 2014. CNS PFS and OS were assessed in patients who received CDK4/6i after BM. OS from the time of BM development was assessed between patients who received CDK4/6i before BM and the CDK-N cohort RESULTS: In the CDK-Y cohort of 363 patients, 203 (56 %) received a CDK4/6i before BM, 133 (37 %) received a CDK4/6i only after BM and 27 (7 %) received a CDK4/6i both before and after BM. Median CNS PFS was 21.4 months for patients receiving a CDK4/6i only after BM and 9.4 months for patients who received CDK4/6i both before and after BM (p = 0.006). Median OS was 24.9 months for patients receiving a CDK4/6i only after BM and 12.1 months for patients who received CDK4/6i both before and after BM (p = 0.0098). Median OS from time of BM development for patients receiving a CDK4/6i before BM versus the CDK-N cohort was 4.3 months and 7.7 months respectively (p = 0.0082).

CONCLUSIONS

CDK4/6i exposure prior to BM may lead to development of resistance mechanisms which in turn reduces CNS PFS and OS upon rechallenging with a CDK4/6i after BM development. This motivates investigation of biomarkers for patient selection.

Comprehensive analysis of stereotactic Radiosurgery outcomes in triple-negative breast cancer patients with brain metastases: The influence of immunotherapy and prognostic factors

INTRODUCTION

Breast cancer stands as the second most common solid tumors with a propensity for brain metastasis. Among metastatic breast cancer cases, the brain metastasis incidence ranges from 10 % to 30 %, with triple-negative breast cancer (TNBC) displaying a heightened risk and poorer prognosis. SRS has emerged as an effective local treatment modality for brain metastases; however, data on its outcomes specifically in pure triple-negative subtype remain scarce.

METHOD

We retrospectively reviewed the electronic medical records of all brain metastasis (BM) TNBC patients treated with SRS. Patient, tumour characteristics and treatment details data were collected. This retrospective cohort study aimed to evaluate local control (LC), distant brain metastasis free survival (DBMFS), and overall survival (OS) outcomes in TNBC patients undergoing SRS for brain metastases while identifying potential prognostic factors.

RESULT

Forty-three patients with TNBC and brain metastases treated with SRS between January 2017 and 2023 were included. The study found rates of LC (99 % at 1 year) and DBMFS (76 % at 1 year) after SRS, with brain metastasis count (p = 0,003) and systemic treatment modality (p = 0,001) being significant predictors of DBMFS. The median OS following SRS was 19.5 months, with neurological deficit (p = 0.003) and systemic treatment modality (p = 0.019) identified as significant predictors of OS.

CONCLUSION

SRS demonstrates favourable outcomes in terms of local control and distant brain metastasis-free survival in TNBC. Neurological deficit and systemic treatment significantly influence overall survival, emphasizing the importance of personalized treatment approaches and (magnetic resonance imaging) MRI surveillance based on these factors.

Impact of brain organoid-derived sEVs on metastatic adaptation and invasion of breast carcinoma cells through a microphysiological system

Brain metastases are common in triple-negative breast cancer (TNBC), suggesting a complex process of cancer spread. The mechanisms enabling TNBC cell adaptation and proliferation in the brain remain unclear. Small extracellular vesicles (sEVs) play a crucial role in communication between breast carcinoma cells and the brain. However, the lack of relevant models hinders understanding of sEV-mediated communication. The present study assesses the impact of brain organoid-derived sEVs (BO-sEVs) on various behaviours of the MDA-MB-231 cell line, chosen as a representative of TNBC in a 3D microfluidic model. Our results demonstrate that 150-200 nm sEVs expressing CD63, CD9, and CD81 from brain organoid media decrease MDA-MB-231 cell proliferation, enhance their wound-healing capacity, alter their morphology into more mesenchymal mode, and increase their stemness. BO-sEVs led to heightened PD-L1, CD49f, and vimentin levels of expression in MDA-MB-231 cells, suggesting an amplified immunosuppressive, stem-like, and mesenchymal phenotype. Furthermore, these sEVs also induced the expression of neural markers such as GFAP in carcinoma cells. The cytokine antibody profiling array also showed that BO-sEVs enhanced the secretion of MCP-1, IL-6, and IL-8 by MDA-MB-231 cells. Moreover, sEVs significantly enhance the migration and invasion of carcinoma cells toward brain organoids in a 3D organoid-on-a-chip system. Our findings emphasize the potential significance of metastatic site-derived sEVs as pivotal mediators in carcinoma progression and adaptation to the brain microenvironment, thereby unveiling novel therapeutic avenues.

Pyrotinib and trastuzumab plus palbociclib and fulvestrant in HR+/HER2+ breast cancer patients with brain metastasis

Human epidermal growth factor receptor 2-positive (HER2+) breast cancer (BC) patients are at a high risk of developing metastases in the brain. However, research focusing on treatment strategies for hormonal receptor positive (HR+), HER2+ BC patients with brain metastases (BM) remains limited. Thus, a multi-center, prospective trial was conducted in China. Women over the age of 18 who were naive to whole brain radiotherapy and had estrogen receptor (ER)/progesterone-receptor (PgR) positive, HER2+ BM were treated with palbociclib, fulvestrant, trastuzumab and pyrotinib, until disease progression or the development of intolerable side effects. The primary endpoint was objective response rate (ORR) in the central nervous system (CNS). This ongoing study is still recruiting participants and is registered with ClinicalTrials.gov (NCT04334330). This report presents the findings from an interim analysis. From December 4, 2020, to November 2, 2022, 15 patients were enrolled. Among the 14 patients who were evaluable for clinical response, the ORR was 35.7% (95% CI: 12.8-64.9%), with a CNS-ORR of 28.6% (95% CI: 8.4-58.1%). The median follow-up period was 6.3 months (range, 2.1-14.3 months), during which the median progression-free survival (PFS) was 10.6 months (95% CI: 4.3-16.9 months), and the median time to CNS progression was 8.5 months (95% CI: 5.9-11.1 months). The most common adverse event was diarrhea (93%), with 33% having grade 3 and 6.7% having grade 4. The study suggests that the combination of palbociclib, trastuzumab, pyrotinib and fulvestrant offers a promising chemo-free treatment strategy for HR+, HER2+ BC patients with BM.

Navigating the Complexities of Brain Metastases Management

The management of brain metastases, a potentially devastating complication of advanced cancers, has become increasingly complex with advancements in local and systemic therapies. Improved outcomes and extended survival for patients with metastatic solid tumors have led to a surge in the prevalence and possibly incidence of brain metastases, affecting up to 40% of individuals with solid tumors. Enhanced imaging technologies contribute to more accurate and early detection, shaping the understanding of the intricate landscape of this condition. Traditionally, surgery and radiation stood as the mainstays of treatment because of the limited efficacy of systemic therapies within the brain. However, emerging clinical data, particularly in melanoma, lung, and breast cancers, reveal promising results with novel systemic treatments such as immunotherapy and targeted therapies. Despite the historical exclusion of patients with active brain metastases from clinical trials, a shift is occurring toward a more inclusive approach. This chapter delves into the multifaceted challenges associated with managing brain metastases, with a focus on the evolving landscape of systemic approaches as well as the intricacies of shared decision making, providing a comprehensive overview of the current state and future directions in navigating the complexities of brain metastases management.

Analysis of Breast Cancer Brain Metastases Reveals an Enrichment of Cyclin-Dependent Kinase 12 Structural Rearrangements in Human Epidermal Growth Factor Receptor 2-Positive Disease

PURPOSE

Genomic alterations have been identified in patients with breast cancer brain metastases (BCBMs), but large structural rearrangements have not been extensively studied.

MATERIALS AND METHODS

We analyzed the genomic profiles of 822 BCBMs and compared them with 11,988 local, breast-biopsied breast cancers (BCs) and 15,516 non-CNS metastases (Non-CNS M) derived from formalin-fixed paraffin-embedded material using targeted capture sequencing.

RESULTS

Nine genes with structural rearrangements were more prevalent within BCBMs as compared with local BCs and Non-CNS M (adjusted-P < .05) and displayed a prevalence of >0.5%. The most common rearrangements within BCBMs involves cyclin-dependent kinase 12 (CDK12; 3.53%) as compared with the local BC (0.86%; adjusted-P = 7.1 × 10-8) and Non-CNS M specimens (0.68%; adjusted-P = 3.7 × 10-10). CDK12 rearrangements had a significantly higher frequency within human epidermal growth factor receptor 2 (HER2)-positive BCBMs (14.59%) compared with HER2-positive BCs (7.80%; P = 4.6 × 10-3) and HER2-positive Non-CNS M (7.87%; P = 4.8 × 10-3).

CONCLUSION

The most common structural rearrangements involve CDK12 with the higher prevalence in HER2-positive BCBMs. These data support more detailed investigation of the role and importance of CDK12 rearrangements in BCBMs.

Navigating breast cancer brain metastasis: Risk factors, prognostic indicators, and treatment perspectives

In this editorial, we comment on the article by Chen et al. We specifically focus on the risk factors, prognostic factors, and management of brain metastasis (BM) in breast cancer (BC). BC is the second most common cancer to have BM after lung cancer. Independent risk factors for BM in BC are: HER-2 positive BC, triple-negative BC, and germline BRCA mutation. Other factors associated with BM are lung metastasis, age less than 40 years, and African and American ancestry. Even though risk factors associated with BM in BC are elucidated, there is a lack of data on predictive models for BM in BC. Few studies have been made to formulate predictive models or nomograms to address this issue, where age, grade of tumor, HER-2 receptor status, and number of metastatic sites (1 vs > 1) were predictive of BM in metastatic BC. However, none have been used in clinical practice. National Comprehensive Cancer Network recommends screening of BM in advanced BC only when the patient is symptomatic or suspicious of central nervous system symptoms; routine screening for BM in BC is not recommended in the guidelines. BM decreases the quality of life and will have a significant psychological impact. Further studies are required for designing validated nomograms or predictive models for BM in BC; these models can be used in the future to develop treatment approaches to prevent BM, which improves the quality of life and overall survival.

Cancer-stromal cell interactions in breast cancer brain metastases induce glycocalyx-mediated resistance to HER2-targeting therapies

Brain metastatic breast cancer is particularly lethal largely due to therapeutic resistance. Almost half of the patients with metastatic HER2-positive breast cancer develop brain metastases, representing a major clinical challenge. We previously described that cancer-associated fibroblasts are an important source of resistance in primary tumors. Here, we report that breast cancer brain metastasis stromal cell interactions in 3D cocultures induce therapeutic resistance to HER2-targeting agents, particularly to the small molecule inhibitor of HER2/EGFR neratinib. We investigated the underlying mechanisms using a synthetic Notch reporter system enabling the sorting of cancer cells that directly interact with stromal cells. We identified mucins and bulky glycoprotein synthesis as top-up-regulated genes and pathways by comparing the gene expression and chromatin profiles of stroma-contact and no-contact cancer cells before and after neratinib treatment. Glycoprotein gene signatures were also enriched in human brain metastases compared to primary tumors. We confirmed increased glycocalyx surrounding cocultures by immunofluorescence and showed that mucinase treatment increased sensitivity to neratinib by enabling a more efficient inhibition of EGFR/HER2 signaling in cancer cells. Overexpression of truncated MUC1 lacking the intracellular domain as a model of increased glycocalyx-induced resistance to neratinib both in cell culture and in experimental brain metastases in immunodeficient mice. Our results highlight the importance of glycoproteins as a resistance mechanism to HER2-targeting therapies in breast cancer brain metastases.