The bone is a common site of metastasis for gastric cancer. High-risk factors of metastatic gastric cancer include young age, poorly differentiated adenocarcinoma, Borrmann type III tumors, depth of invasion at Se and Pm levels, positive lymph nodes, and gastric cancer with concomitant body of stomach cancer. More than half of the transfer pathway belongs to the non-portal system. Cases of gastric cancer with bone metastasis but without liver metastasis accounted for 69%of the total gastric cancer cases, whereas the incidence rate of bone metastasis with lymph node metastasis (≥3 cm away from the primary lesion) was 27%. In addition to the tumor markers human chorionic gonadotropin and carcinoembryonic antigen, radionuclide scan of the bone metastasis provides diagnostic pathways and reliable basis for treatment. Chemoradiation and surgery as symptomatic treatments are alternative therapies for stomach cancer. Bone metastasis confers unfavorable prognosis, and the survival time is often less than six months.

Brain cell-derived extracellular vesicles （BCDEVs） are a group of double-layer membrane-structured nanovesicles which are released by all neural cells in the central nervous system （CNS） and contain the heterogeneity of the biological molecules of their originating cells， and under the physiological and pathological conditions of the brain， they are becoming the key media for communication and waste management between neurons， glial cells， and connective tissue. Based on the different specific molecular markers on the surface of BCDEVs， researchers have successfully enriched different subtypes of BCDEVs from peripheral blood， including neuron-derived extracellular vesicles， astrocytes-derived extracellular vesicles，oligodendrocyte-derived extracellular vesicles， microglia-derived extracellular vesicles， pericyte-derived extracellular vesicles，and endotheliocyte-derived extracellular vesicles. This article reviews extracellular vesicles， summarizes the different specific molecular markers used to enrich different BCDEVs from peripheral blood， and introduces the application of peripheral blood BCDEVs in CNS diseases，so as to clarify their potential as a biomarker and the challenges they face in achieving this goal.