Therefore, circulating exosomes may be useful tools for early detection in patients with MM. Acquired resistance is a major obstacle to tumor chemotherapy. Compared with healthy people, the expression level of serum exosomal circMYC was significantly increased in patients with MM. In addition, the expression of circMYC in circulating exosomes in bortezomib-resistant patients was significantly higher than that in non-resistant patients. The expression level of exosomal circMYC was correlated with deletion 17p, t(4;14), Durie-Salmon staging, and the International Staging System. Univariate and multivariate Cox regression analysis found that a high exosomal circMYC level was an independent predictor of poor prognosis in patients with MM. The patients with high exosome circMYC expression had higher relapse rates and higher mortality rates. The overall survival rate and progression-free survival rate of MM patients with high exosomal circMYC expression were lower than those of patients with low exosomal circMYC expression. Conclusion: These findings suggest that circulating exosomal circMYC has great potential as a biomarker for the diagnosis and prognosis of MM. gene and contains an exon circRNA transcript located on chromosome 8. CircMYC has been reported to promote the proliferation of breast cancer cells  and human melanoma cells . However, the expression of circulating exosomal circMYC in patients with MM and its role in prognostic evaluation remain unclear. This study focused on the expression of circMYC in the serum exosomes of patients with MM and its role in the evaluation of relapse and drug resistance in these patients. Materials and Methods Human Samples From January 2014 to January 2019, we collected peripheral serum samples and clinical case data of 122 patients diagnosed with MM in our hospital. We also collected the clinical and pathological data of the patients, including age (ranging from 41 to 76 years old), gender (79 male and 43 female patients), EMD534085 disease classification, and clinical stage [Durie-Salmon staging (DSS) and International Staging System (ISS)]. The diagnosis of MM patients was based on the diagnostic criteria of the International Myeloma Working Group . In addition, 54 peripheral serum samples from healthy individuals were collected as a control group. The healthy controls were included based on the following criteria: no previous history of malignant tumors, and normal liver and kidney functions. The study was approved by the Ethics Committee of The Third Xiangya Hospital, Central South University. All subjects signed the informed consent form. Exosome Isolation and Identification The serum was thawed on ice and then centrifuged at 2000x g for 30 min at 4 C to F2r remove debris. The supernatant was filtered through a 0.22-m filter. The filtered supernatant EMD534085 was then transferred to a 50-mL ultrafiltration tube. The exosomes were extracted using an exosome isolation kit (EXOTC50A-1, System Biosciences, Palo Alto, CA, USA). Briefly, 0.5 times the volume of the extraction reagent was added and mixed well with the filtered supernatant, and this mixture was incubated at 4 C overnight. After that, the samples were centrifuged at 10000x g for 60 min at 4 C. The supernatant was discarded, and the exosome pellets were resuspended in PBS. Samples of 10 L were used for transmission electron microscopy observations, and 100 L was used for RNA extraction and quantitative polymerase chain reaction (qPCR) analysis. Transmission Electron Microscopy to Observe Exosomes The morphologies of the exosomes were EMD534085 EMD534085 observed by EMD534085 transmission electron microscopy as previously described . Briefly, the exosomes were fixed with 4% glutaraldehyde solution and then stained with phosphotungstic acid (2%) for 30 s. Morphology was observed under a transmission electron microscope at an acceleration voltage of 80 kV. Ribonuclease R Treatment Ribonuclease R (RNase R) digests almost all linear RNA molecules, but it is not easy to digest circular RNAs. RNase R can be used to digest linear RNA and identify circular RNAs . RNase R (10 U; Geneseed, Guangzhou, China) was added to 2.5 g of total RNA and mixed well for.