Cancer exosomes in cerebrospinal fluid

Cancer cells secrete extracellular vesicles (EVs), including exosomes, which contain a varied cargo of tumour-specific genetic material such as DNA, mRNA and miRNA. EVs possess the ability to manipulate various functional and pathological characteristics of the donor and recipient cells, in addition to facilitating modifications of the tumour microenvironment, firstly during disease progression and also in response to clinical treatment. ‘Liquid biopsy’ platforms, such as blood based tests for monitoring cancer progression and response to therapeutics, have been part of oncologic care for decades. However, further development of biofluid-based methodologies is required as an important step not only in tumour characterization and the ongoing monitoring of the disease, but also as a basis for creating novel therapies for treating cancer patients. Cerebrospinal fluid (CSF) is another accessible body fluid which can provide an overview of the pathological state of central nervous system (CNS) malignancies such as gliomas. Glioma cells are known to secrete EVs, including exosomes, and CSF is recognized as a route for the potential seeding of invasive cells of CNS tumours. This suggests that CSF-derived exosomes are a promising source of biomarkers that not only have the capacity to mirror the genetic diversity within a tumour at any one time, but to also enable the longitudinal measurements for monitoring genetic changes in the tumour during treatment without the need for repeated tissue biopsies. In this review, we examine the current scientific literature on our current understanding of exosomes in glioma and the relevance of CSF-derived exosomes in this disease.