Biological Insights and Radiation–Immuno–Oncology Developments in Primary and Secondary Brain Tumors.

Simple Summary: Brain cancers, which can start in the brain or spread there from other parts of the body, are difficult to treat and often lead to severe health issues and death. Radiotherapy (RT) is a main treatment that helps control symptoms and can sometimes cure the disease, but many brain cancers resist it, especially those that start in the brain. Combining immunotherapy with RT has shown promise for treating cancers that spread to the brain, but has limited success with gliomas, the most common primary brain cancer. This review looks at why brain tumors resist RT, new strategies to overcome this, and the role of the tumor's environment. We highlight key findings from recent research and identify new treatment opportunities to improve outcomes and survival rates for brain cancer patients. Malignant central nervous system (CNS) cancers include a group of heterogeneous dis-eases characterized by a relative resistance to treatments and distinguished as either primary tumors arising in the CNS or secondary tumors that spread from other organs into the brain. Despite therapeutic efforts, they often cause significant mortality and morbidity across all ages. Radiotherapy (RT) remains the main treatment for brain cancers, improving associated symptoms, improving tumor control, and inducing a cure in some. However, the ultimate goal of cancer treatment, to improve a patient's survival, remains elusive for many CNS cancers, especially primary tumors. Over the years, there have thus been many preclinical studies and clinical trials designed to identify and overcome mechanisms of resistance to improve outcomes after RT and other therapies. For example, immunotherapy delivered concurrent with RT, especially hypo-fractionated stereotactic RT, is synergistic and has revolutionized the clinical management and outcome of some brain tumors, in particular brain metastases (secondary brain tumors). However, its impact on gliomas, the most common primary malignant CNS tumors, remains limited. In this review, we provide an overview of radioresistance mechanisms, the emerging strategies to overcome radioresistance, the role of the tumor microenviroment (TME), and the selection of the most significant results of radiation–immuno–oncological investigations. We also identify novel therapeutic opportunities in primary and secondary brain tumors with the purpose of elucidating current knowledge and stimulating further research to improve tumor control and patients' survival. [ABSTRACT FROM AUTHOR]