Abstract: Objective To explore the expression level of serum exosomal Glypican-1 (GPC-1) in patients with breast cancer and its clinical application value. 
Methods A total of 48 patients diagnosed with breast cancer, and 18 patients diagnosed with benign breast mass in the Fourth Hospital of Hebei Medical University were selected. Another 17 healthy subjects undergoing physical examination during the same period were selected as healthy control group. Serum exosomes were extracted by polyethylene glycol 8000 precipitation method, and the morphology and molecular phenotype of exosomes were identified by transmission electron microscopy and western blotting. Western blotting was used to detect the expression level of serum exosomal GPC-1 in each group. Receiver operating characteristic (ROC) curve was used to evaluate the diagnostic efficacy of serum exosomal GPC-1 for breast cancer. With the best cut-off value of 0.961, the breast cancer group was divided into GPC-1 positive group and GPC-1 negative group, to analyze the relationship between GPC-1 and clinical characteristics. The Wilcoxon rank sum test was used to analyze the changes of serum exosomal GPC-1 expression in breast cancer group before and after treatment. Taking pathological diagnosis as the gold standard, Kappa consistency test was used to evaluate the diagnostic value of four diagnostic methods, serum exosomal GPC-1, serum tumor markers, B-ultrasound, and mammography, for breast cancer. 
Results The expression level of serum exosomal GPC-1 in the breast cancer group ［1.065(0.501)］ was higher than that of the benign breast mass group ［0.652(0.117)］ and the healthy control group ［0.625(0.139)］, and the difference was statistically significant(H=32.051, P＜0.05). The area under the ROC curve (AUC) was 0.900 (95%CI:0.833-0.967), and the optimal cut-off value was 0.961, which could be used to effectively screen breast cancer patients. GPC-1 positivity in breast cancer group was significantly correlated with TNM stage, lymph node invasion and Ki-67 high expression(all P＜0.05). The expression level of serum exosomal GPC-1 in the breast cancer group before treatment ［1.065(0.501)］ was higher than that at 20 d after treatment ［0.844(0.195)］, and the difference was statistically significant. The Kappa value of the serum exosomal GPC-1 detection method was 0.485＞0.4, which was moderately consistent with pathological examination and was superior to the other three detection methods. 
Conclusion The expression of serum exosomal GPC-1 in the breast cancer group is up-regulated, which is associated with multiple adverse clinical characteristics, and significantly decreases after treatment. Therefore, it has the potential to be used as an index for the diagnosis and treatment of breast cancer.

Key words: breast neoplasms, exosome, GPC-1