CD63 and glioblastoma: For this reason, they explored PTRF’s ability as biomarker: firstly, they proved PTRF’s presence on exosomes’ surfaces and the capability of improving EV secretion and GBM cell proliferation; secondly, they analyzed the PTRF/CD63 ratio in tumor samples and relative donated blood from 18 WHO grade II and grade IV samples, finding that a higher PTRF/CD63 ratio at the protein level was detected in WHO grade IV samples in both tumor tissues and serum exosomes, indicating a more selective prognosis.