A groundbreaking discovery has shed new light on the complex world of brain metastases, offering hope for more effective treatment strategies. The key to unlocking this mystery lies in understanding the unique interaction between cancer cells and the brain's microenvironment.
An ambitious research collaboration, led by experts from the LKS Faculty of Medicine and the Faculty of Dentistry at the University of Hong Kong, has resulted in the creation of the world's largest multi-omics atlas of brain metastases. This comprehensive study analyzed an impressive 1,032 brain metastasis samples from various primary tumors, along with 82 matched primary tumors and 20 glioblastomas as controls. The findings provide an innovative framework for classifying brain metastases and lay the foundation for personalized treatment approaches, pushing the boundaries of precision oncology.
Brain metastases occur when cancer cells from primary sites, such as the lung, breast, or skin, spread to the brain. Despite advancements in surgery, radiotherapy, and systemic therapies, brain metastases present a significant challenge due to their heterogeneity. This makes it difficult to identify universal effective treatments, and as a result, brain metastases remain a leading cause of cancer-related deaths, affecting a substantial 30% of patients with advanced-stage solid tumors.
But here's where it gets controversial... Previous research primarily focused on the characteristics of the primary tumor, overlooking the unique biological changes that cancer cells undergo when they interact with the brain microenvironment. Professor Zhang Gao, an Associate Professor at HKU's Faculty of Dentistry and co-leader of the study, explains their hypothesis: 'Once cancer cells spread to the brain, they evolve into several molecular subtypes, regardless of their original site. These subtypes are shaped by the unique brain microenvironment, not by the primary tissue. This represents a paradigm shift in our understanding and treatment of brain metastases.'
The research team integrated various data types, including genomic, transcriptomic, proteomic, and spatial data, from the 1,032 brain metastasis samples. This led to the identification of four distinct brain metastasis subtypes: Neural-like (BrMS1), Immune-infiltrated (BrMS2), Metabolic (BrMS3), and Proliferative (BrMS4). Each subtype exhibits unique immune landscapes, metabolic programs, biological features, and potential therapeutic targets.
The 'Neural-like subtype' expresses neural-related genes, displaying brain-like characteristics associated with the microenvironment. It is sensitive to radiotherapy. The 'Immune-infiltrated subtype' has abundant immune cell infiltration, leading to the longest overall survival and potentially better responses to immunotherapy. The 'Metabolic subtype' shows abnormally active energy metabolism pathways, suggesting that metabolism-targeted therapies may be effective. The 'Proliferative subtype' is characterized by high cell proliferation and a poorer prognosis, with activated proliferation-related pathways indicating potential for targeted interventions.
Building on these unique biological characteristics, the research team explored the development of personalized treatment strategies for each subtype. They found that the 'Neural-like' and 'Immune-infiltrated' subtypes had higher levels of cytotoxic T lymphocytes (CTLs) and more active immune checkpoint molecules like PD-L1 and CTLA4, suggesting better responses to immune checkpoint blockade therapy. The 'Immune-infiltrated subtype' had the most abundant immune cells, which could be stimulated by immunotherapy drugs to restore their tumor-fighting capacity. Additionally, CTL infiltration level was found to be an independent prognostic indicator, with higher levels correlating to longer overall survival rates.
To validate the differences in sensitivity to targeted therapies, the team employed patient-derived organoid models for drug screening. Functional experiments showed that the 'Metabolic subtype' responded better to mTOR inhibitors, while the 'Proliferative subtype' was more sensitive to CDK4/6 inhibitors.
Professor Gilberto Leung Ka-kit, Tsang Wing-Hing Professor in Clinical Neuroscience and Clinical Professor in the Department of Surgery at HKUMed, emphasized the challenges posed by the brain's immunosuppressive environment and the blood-brain barrier. 'Our research highlights how different tumor subtypes interact with brain neurons and immune cells. This knowledge paves the way for innovative combinations of targeted drugs, immunotherapy, and radiotherapy to find effective treatments.'
Professor Liu Lunxu from West China Hospital of Sichuan University and co-leader of the study, highlighted the power of multi-institutional collaboration: 'By combining expertise from across China and Hong Kong, we were able to create an unprecedented dataset. This successful partnership demonstrates how collaborative science can accelerate progress in precision oncology and benefit patients with brain metastases.'
This research was supported by various funding bodies, including the Research Grants Council and the Government of the Hong Kong Special Administrative Region. Tumor tissue samples were provided by multiple hospitals, including Queen Mary Hospital in Hong Kong, Sun Yat-sen University Cancer Center, Beijing Tiantan Hospital, and West China Hospital of Sichuan University.
The findings of this study offer a glimmer of hope for patients with brain metastases, providing a more nuanced understanding of these complex tumors and opening up new avenues for personalized treatment approaches.
