CD109 and cancer: Among the proteins over-expressed in GBM-sEVs, we found tenascin C (TNC), an extracellular matrix molecule that drives the progression of many types of human cancer, including GBM [66]; CD109, which is associated with stemness maintenance and disease recurrence [67]; CD44, which has been implicated in malignant processes including cell motility, tumor growth, and angiogenesis in many cancer types and has been proposed as an invasion and migration marker in GBM [68]; and Ras suppressor protein 1 (RSU1), which is highly expressed in more aggressive GBM cells, promoting cell invasion [69].