Breast cancer brain metastases: the last frontier

The Hidden Morbidity of Cancer: Burden in Caregivers of Patients with Brain Metastases

Caregiving is a highly individualized experience. Although numerous articles have been published on caregiver burden from a variety of diagnoses and conditions, this article presents the unique features of caregiving in patients with brain metastases. Improved long-term survival, concerns about disease recurrence or progression, the cancer experience (initial diagnosis, treatment, survivorship, recurrence, progression, and end of life), and the increasing complexity of cancer treatments add to the demands placed on the caregivers of patients with brain metastases. Health care professionals must identify caregiver burden and administer the appropriate interventions, which must be as unique and individualized as the caregivers' experiences.

Cooperation of neurotrophin receptor TrkB and Her2 in breast cancer cells facilitates brain metastases

BACKGROUND

Patients with primary breast cancer that is positive for human epidermal growth factor receptor 2 (Her2+) have a high risk of developing metastases in the brain. Despite gains with systemic control of Her2+ disease using molecular therapies, brain metastases remain recalcitrant to therapeutic discovery. The clinical predilection of Her2+ breast cancer cells to colonize the brain likely relies on paracrine mechanisms. The neural niche poses unique selection pressures, and neoplastic cells that utilize the brain microenvironment may have a survival advantage.

METHODS

Tropomyosin-related kinase B (TrkB), Her2, and downstream targets were analyzed in primary breast cancer, breast-to-brain metastasis (BBM) tissues, and tumor-derived cell lines using quantitative real-time PCR, western blot, and immunohistochemical assessment. TrkB function on BBM was confirmed with intracranial, intracardiac, or mammary fat pad xenografts in non-obese diabetic/severe combined immunodeficiency mice. The function of brain-derived neurotrophic factor (BDNF) on cell proliferation and TrkB/Her2 signaling and interactions were confirmed using selective shRNA knockdown and selective inhibitors. The physical interaction of Her2-TrkB was analyzed using electron microscopy, co-immunoprecipitation, and in silico analysis. Dual targeting of Her2 and TrkB was analyzed using clinically utilized treatments.

RESULTS

We observed that patient tissues and cell lines derived from Her2+ human BBM displayed increased activation of TrkB, a neurotrophin receptor. BDNF, an extracellular neurotrophin, with roles in neuronal maturation and homeostasis, specifically binds to TrkB. TrkB knockdown in breast cancer cells led to decreased frequency and growth of brain metastasis in animal models, suggesting that circulating breast cancer cells entering the brain may take advantage of paracrine BDNF-TrkB signaling for colonization. In addition, we investigated a possible interaction between TrkB and Her2 receptors on brain metastatic breast cancer cells, and found that BDNF phosphorylated both its cognate TrkB receptor and the Her2 receptor in brain metastatic breast cancer cells.

CONCLUSION

Collectively, our findings suggest that heterodimerization of Her2 and TrkB receptors gives breast cancer cells a survival advantage in the brain and that dual inhibition of these receptors may hold therapeutic potential.

Brain metastases from hepatocellular carcinoma: recent advances and future avenues

The incidence of brain metastases from hepatocellular carcinoma (BMHCC) is becoming more frequent than that of the past as a result of prolonged survival of patients with HCC. Compared with brain metastases from other types of cancer, BMHCC tends to exhibit a high incidence of intracerebral hemorrhage (ICH) and poor liver function. Unfortunately, the prognosis is extremely poor for patients with BMHCC owing to the limited treatment selection. Currently, optimal treatment requires multidisciplinary approaches including surgery, whole-brain radiation therapy and stereotactic radiosurgery. Besides these traditional approaches, novel treatments such as target therapy and immunotherapy provide an opportunity to improve the survival of these patients. This review provides an overview of the incidence, characteristics, prognosis, and current and potential future management strategies for BMHCC.

Triple-negative breast cancer with brain metastasis in a pregnant woman

A woman aged 35 years was diagnosed with triple-negative breast cancer in October 2012. During the investigation, it was discovered that she was pregnant, the patient decided to have an abortion. She was submitted to a radical modified mastectomy and adjuvant chemotherapy followed by adjuvant breast radiotherapy of the left breast. 2 months after the adjuvant treatment, she began to have headaches and dizziness. The cranial MRI (head MRI) showed brain metastasis. She was then treated with whole brain radiotherapy, stereotactic radiosurgery and concomitant temozolomide which resulted in complete response. 1.5 year later, she was able to get pregnant and gave birth to a baby without complications. The previous imaging reassessment performed in September 2016 shows no evidence of recurrent breast cancer.

Prognostic factors and survival according to tumour subtype in women presenting with breast cancer brain metastases at initial diagnosis

BACKGROUND

The presence of brain metastases at the time of initial breast cancer diagnosis (BMIBCD) is uncommon. Hence, the prognostic assessment and management of these patients is very challenging. The aim of this study was to analyse the influence of tumour subtype compared with other prognostic factors in the survival of patients with BMIBCD.

METHODS

We evaluated women with BMIBCD, reported to Surveillance, Epidemiology and End Results program from 2010 to 2013. Patients with other primary malignancy were excluded. Univariate and multivariate analyses were performed to determine the effects of each variable on overall survival (OS).

RESULTS

We included 740 patients. Median OS for the whole population was 10 months, and 20.7% of patients were alive at 36 months. Tumour subtype distribution was: 46.6% hormone receptor (HR)+/HER2-, 17% HR+/HER2+, 14.1% HR-/HER2+ and 22.3% triple-negative. Univariate analysis showed that the presence of liver metastases, lung metastases and triple-negative patients (median OS 6 months) had worse prognosis. The HR+/HER2+ subtype had the longest OS with a median of 22 months. In multivariate analysis, older age (hazard ratio 1.8), lobular histology (hazard ratio 2.08), triple-negative subtype (hazard ratio 2.25), liver metastases (hazard ratio 1.6) and unmarried patients (hazard ratio 1.39) had significantly shorter OS.

CONCLUSIONS

Although the prognosis of patients with BMIBCD is generally poor, 20.7% were still alive 3 years after the diagnosis. There were substantial differences in OS according to tumour subtype. In addition to tumour subtype, other independent predictors of OS are age at diagnosis, marital status, histology and liver metastases.

In vivo magnetic resonance imaging investigating the development of experimental brain metastases due to triple negative breast cancer

Triple negative breast cancer (TNBC), when associated with poor outcome, is aggressive in nature with a high incidence of brain metastasis and the shortest median overall patient survival after brain metastasis development compared to all other breast cancer subtypes. As therapies that control primary cancer and extracranial metastatic sites improve, the incidence of brain metastases is increasing and the management of patients with breast cancer brain metastases continues to be a significant clinical challenge. Mouse models have been developed to permit in depth evaluation of breast cancer metastasis to the brain. In this study, we compare the efficiency and metastatic potential of two experimental mouse models of TNBC. Longitudinal MRI analysis and end point histology were used to quantify initial cell arrest as well as the number and volume of metastases that developed in mouse brain over time. We showed significant differences in MRI appearance, tumor progression and model efficiency between the syngeneic 4T1-BR5 model and the xenogeneic 231-BR model. Since TNBC does not respond to many standard breast cancer treatments and TNBC brain metastases lack effective targeted therapies, these preclinical TNBC models represent invaluable tools for the assessment of novel systemic therapeutic approaches. Further pursuits of therapeutics designed to bypass the blood tumor barrier and permit access to the brain parenchyma and metastatic cells within the brain will be paramount in the fight to control and treat lethal metastatic cancer.

Clinical features of brain metastases in breast cancer: an implication for hippocampal-sparing whole-brain radiation therapy

Objective

The objectives of this study were to describe the distribution of brain metastases (BM) in breast cancer patients and investigate the risk factors for perihippocampal metastases (PHM).

Patients and methods

Retrospective analysis of the clinicopathological characteristics and patterns of BM was performed. Associations between clinicopathological characteristics and PHM (the hippocampus plus 5 mm margin) were evaluated using logistic regression analyses.

Results

A total of 1,356 brain metastatic lesions were identified in 192 patients. Patients with 1–3 BM, 4–9 BM, and ≥10 BM accounted for 63.0%, 18.8%, and 18.2%, respectively. There were only 7 (3.6%) patients with hippocampal metastases (HM) and 14 (7.3%) patients with PHM. On logistic regression, the number of BM was an independent risk factor for PHM. Patients with ≥10 BM had a significantly higher risk of PHM compared with those with <10 BM. Breast cancer subtype (BCS) was not associated with PHM. The number of BM was significantly correlated with various BCSs. Patients with hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)+, HR−/HER2+, and HR−/HER2− subtypes had a higher probability of ≥10 BM, relative to patients with an HR+/HER2− subtype.

Conclusion

Our study suggests that a low incidence of PHM may be acceptable to perform hippocampal-sparing whole-brain radiation therapy for breast cancer patients. Patients with extensive diffuse metastases (≥10 BM) were associated with higher odds of PHM.

Targeted Therapies for Brain Metastases from Breast Cancer

The discovery of various driver pathways and targeted small molecule agents/antibodies have revolutionized the management of metastatic breast cancer. Currently, the major targets of clinical utility in breast cancer include the human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF) receptor, mechanistic target of rapamycin (mTOR) pathway, and the cyclin-dependent kinase 4/6 (CDK-4/6) pathway. Brain metastasis, however, remains a thorn in the flesh, leading to morbidity, neuro-cognitive decline, and interruptions in the management of systemic disease. Approximately 20%–30% of patients with metastatic breast cancer develop brain metastases. Surgery, whole brain radiation therapy, and stereotactic radiosurgery are the traditional treatment options for patients with brain metastases. The therapeutic paradigm is changing due to better understanding of the blood brain barrier and the advent of tyrosine kinase inhibitors and monoclonal antibodies. Several of these agents are in clinical practice and several others are in early stage clinical trials. In this article, we will review the common targetable pathways in the management of breast cancer patients with brain metastases, and the current state of the clinical development of drugs against these pathways.

Perillyl Alcohol and Its Drug-Conjugated Derivatives as Potential Novel Methods of Treating Brain Metastases

Metastasis to the central nervous system remains difficult to treat, and such patients are faced with a dismal prognosis. The blood-brain barrier (BBB), despite being partially compromised within malignant lesions in the brain, still retains much of its barrier function and prevents most chemotherapeutic agents from effectively reaching the tumor cells. Here, we review some of the recent developments aimed at overcoming this obstacle in order to more effectively deliver chemotherapeutic agents to the intracranial tumor site. These advances include intranasal delivery to achieve direct nose-to-brain transport of anticancer agents and covalent modification of existing drugs to support enhanced penetration of the BBB. In both of these areas, use of the natural product perillyl alcohol, a monoterpene with anticancer properties, contributed to promising new results, which will be discussed here.

Vinorelbine Delivery and Efficacy in the MDA-MB-231BR Preclinical Model of Brain Metastases of Breast Cancer

PURPOSE

To evaluate vinorelbine drug exposure and activity in brain metastases of the human MDA-MB-231BR breast cancer model using integrated imaging and analysis.

METHODS

Brain and systemic metastases were created by administration of cancer cells in female NuNu mice. After metastases developed, animals were administered vinorelbine at the maximal tolerated dose (12 mg/kg), and were evaluated thereafter for total and unbound drug pharmacokinetics, biomarker TUNEL staining, and barrier permeability to Texas red.

RESULTS

Median brain metastasis drug exposure was 4-fold greater than normal brain, yet only ~8% of non-barrier systemic metastases, which suggests restricted brain exposure. Unbound vinorelbine tissue/plasma partition coefficient, K_p,uu, equaled ~1.0 in systemic metastases, but 0.03-0.22 in brain metastases, documenting restricted equilibration. In select sub-regions of highest drug-uptake brain metastases, K_p,uu approached 1.0, indicating complete focal barrier breakdown. Most vinorelbine-treated brain metastases exhibited little or no positive early apoptosis TUNEL staining in vivo. The in vivo unbound vinorelbine IC₅₀ for TUNEL-positive staining (56 nM) was 4-fold higher than that measured in vitro (14 nM). Consistent with this finding, P-glycoprotein expression was observed to be substantially upregulated in brain metastasis cells in vivo.

CONCLUSIONS

Vinorelbine exposure at maximum tolerated dose was less than one-tenth that in systemic metastases in >70% of brain metastases, and was associated with negligible biomarker effect. In small subregions of the highest uptake brain metastases, compromise of blood-tumor barrier appeared complete. The results suggest that restricted delivery accounts for 80% of the compromise in drug efficacy for vinorelbine against this model.

Adapting coculture in vitro models of the blood-brain barrier for use in cancer research: maintaining an appropriate endothelial monolayer for the assessment of transendothelial migration

Although brain metastases are the most common brain tumors in adults, there are few treatment options in this setting. To colonize the brain, circulating tumor cells must cross the blood-brain barrier (BBB), which is situated within specialized, restrictive microvascular endothelium. Understanding how cancer cells manage to transmigrate through the BBB might enable this process to be prevented. In vitro models are dedicated tools for characterizing the cellular and molecular mechanisms that underlie transendothelial migration process, as long as they accurately mimic the brain endothelium's in vivo characteristics. The objective of the present study was to adapt an existing in vitro model of the human BBB for use in studying cancer cell transmigration. The model is based on the coculture of endothelial cells (ECs, derived from cord blood hematopoietic stem cells) and brain pericytes. To allow the migration of cancer cells into the lower compartment, our model had to be transposed onto inserts with a larger pore size. However, we encountered a problem when culturing ECs on large (3-μm)-pore inserts: the cells crossed the membrane and formed a non-physiological second layer on the lower face of the insert. Using 3-μm-pore inserts (in a 12-well plate format), we report here on a method that enables the maintenance of a single monolayer of ECs on the insert's upper face only. Under these chosen conditions, the ECs exhibited typical BBB properties found in the original model (including restricted paracellular permeability and the expression of continuous tight junctions). This modified in vitro model of the human BBB enabled us to investigate the migratory potential of the MDA-MB-231 cell line (derived from highly metastatic human breast cancer cells). Last, the results obtained were compared with the rate of transmigration through endothelia with no BBB features.

Stereotactic Radiosurgery as Part of Multimodal Treatment in a Bulky Leptomeningeal Recurrence of Breast Cancer

Breast cancer metastatic to the brain and/or leptomeningeal spread of disease is a frequently encountered clinical situation, especially given the extended course of disease in these patients. Systemic therapies can often effectively prolong extracranial disease control, making effective strategies to control central nervous system-based disease even more critical. We present a case of bulky leptomeningeal relapse of breast cancer in the setting of prior whole brain radiation therapy. In order to treat the patient’s bulky disease and leptomeningeal spread while avoiding the potential toxicities of repeat whole brain radiation, the patient was treated with frameless stereotactic radiosurgery and intrathecal chemotherapy. This is the first report of this treatment approach for leptomeningeal relapse of breast cancer. The patient had an excellent response to treatment and durable intracranial control.