Emerging Biomarkers for Diagnosis, Prevention and Treatment of Brain Metastases-From Biology to Clinical Utility

Primary malignancies of the lung, skin (melanoma), and breast have higher propensity for metastatic spread to the brain. Advances in molecular tumour profiling have aided the development of targeted therapies, stereotactic radiotherapy, and immunotherapy, which have led to some improvement in patient outcomes; however, the overall prognosis remains poor. Continued research to identify new prognostic and predictive biomarkers is necessary to further impact patient outcomes, as this will enable better risk stratification at the point of primary cancer diagnosis, earlier detection of metastatic deposits (for example, through surveillance), and more effective systemic treatments. Brain metastases exhibit considerable inter- and intratumoural heterogeneity-apart from distinct histology, treatment history and other clinical factors, the metastatic brain tumour microenvironment is incredibly variable both in terms of subclonal diversity and cellular composition. This review discusses emerging biomarkers; specifically, the biological context and potential clinical utility of tumour tissue biomarkers, circulating tumour cells, extracellular vesicles, and circulating tumour DNA.

Predicting early brain metastases based on clinicopathological factors and gene expression analysis in advanced HER2-positive breast cancer patients

The overexpression or amplification of the human epidermal growth factor receptor 2 gene (HER2/neu) is associated with high risk of brain metastasis (BM). The identification of patients at highest immediate risk of BM could optimize screening and facilitate interventional trials. We performed gene expression analysis using complementary deoxyribonucleic acid-mediated annealing, selection, extension and ligation and real-time quantitative reverse transcription PCR (qRT-PCR) in primary tumor samples from two independent cohorts of advanced HER2 positive breast cancer patients. Additionally, we analyzed predictive relevance of clinicopathological factors in this series. Study group included discovery Cohort A (84 patients) and validation Cohort B (75 patients). The only independent variables associated with the development of early BM in both cohorts were the visceral location of first distant relapse [Cohort A: hazard ratio (HR) 7.4, 95 % CI 2.4-22.3; p < 0.001; Cohort B: HR 6.1, 95 % CI 1.5-25.6; p = 0.01] and the lack of trastuzumab administration in the metastatic setting (Cohort A: HR 5.0, 95 % CI 1.4-10.0; p = 0.009; Cohort B: HR 10.0, 95 % CI 2.0-100.0; p = 0.008). A profile including 13 genes was associated with early (≤36 months) symptomatic BM in the discovery cohort. This was refined by qRT-PCR to a 3-gene classifier (RAD51, HDGF, TPR) highly predictive of early BM (HR 5.3, 95 % CI 1.6-16.7; p = 0.005; multivariate analysis). However, predictive value of the classifier was not confirmed in the independent validation Cohort B. The presence of visceral metastases and the lack of trastuzumab administration in the metastatic setting apparently increase the likelihood of early BM in advanced HER2-positive breast cancer.

Optimal management of brain metastases from breast cancer. Issues and considerations

The incidence of brain metastases (BM) in breast cancer patients has increased over the last decade, presumably due to advances in systemic treatment. Today, breast cancer is the second most common cause of BM among all solid malignancies, second only to lung cancer; furthermore, it is the most common cause of leptomeningeal carcinomatosis. The HER2-positive subtype was consistently shown to have a higher risk for BM as compared with HER2-negative disease. More recently, however, it was shown that a similar incidence exists in triple-negative tumours. Local treatment options, radiotherapy and neurosurgical resection, remain the mainstay of therapy for BM. While some studies have suggested a direct effect of conventional chemotherapy on BM, the main beneficial aspect of systemic treatment is rather due to control of non-CNS systemic disease. Importantly, in patients with HER2-positive breast cancer receiving HER2-targeted therapy after local treatment for BM, superior survival outcomes were reported. Leptomeningeal carcinomatosis has a dismal prognosis. Survival with whole brain radiotherapy alone remains short and the potential additional benefit of intrathecal chemotherapy is still disputed. According to case reports, intrathecal administration of trastuzumab appears to be a promising strategy in patients with HER2-positive leptomeningeal carcinomatosis. In conclusion, while the outcome of breast cancer patients with BM has improved especially in the HER2-positive subtype, the prognosis for the majority of patients remains poor. Therefore, development of novel systemic treatment options offering activity within the brain is urgently warranted. Novel insights into the pathobiology of BM formation may offer the possibility for targeted drug prophylaxis of CNS involvement in high-risk patients.

Emerging treatment options for the management of brain metastases in patients with HER2-positive metastatic breast cancer

The widespread use of trastuzumab in the past decade has led to a significant and measureable improvement in the survival of patients with human epidermal growth factor receptor-2 (HER2) overexpressing breast cancer, and in many ways has redefined the natural history of this aggressive breast cancer subtype. Historically, survival in patients with HER2-positive disease was dictated by the systemic disease course, and what appears to be the central nervous system (CNS) tropism associated with HER2-amplified tumors was not clinically evident. With improved systemic control and prolonged survival, the incidence of brain metastases has increased, and CNS disease, often in the setting of well-controlled extracranial disease, is proving to be an increasingly important and clinically challenging cause of morbidity and mortality in patients with HER2-positive advanced breast cancer. This review summarizes the known clinical data for the systemic treatment of HER2-positive CNS metastases and includes information about ongoing clinical trials of novel therapies as well as emerging strategies for early detection and prevention.