Abstract: ObjectiveTo investigate the serum microRNA30 （miR30） level in gastric cancer patients and analyze its relationship with clinicopathological features and prognosis. 
MethodsThe serum samples of 108 patients with gastric cancer from March 2014 to May 2017 and 100 health examiners in the same period were collected， and the miR30 levels in the above samples were detected by realtime quantitative PCR （QPCR）. The difference of miR30 level between the patients with gastric cancer and the health examiners were compared. The values of the miR30 level were divided into the lowexpression group （＜average value） and the highexpression group （＞average value）. The relationship between miR30 level and clinicopathological parameters （gender， age， lymph node metastasis， tumor size， TNM staging， depth of infiltration， Lauren classification and differentiation） was analyzed， and the prognosis of different serum miR30 levels was compared according to the followup data. 
ResultsThe serum miR30 level of gastric cancer patients was 0624±0075， lower than 1028±0094 of the control group， and the difference was statistically significant （P＜005）. The results of ROC curve analysis showed that the area under the curve of miR30 for diagnosis of gastric cancer was 0802 （95％CI： 07420861， P＜0001）. When the diagnostic threshold was 0798， the sensitivity was 759％ and the specificity was 76％. Serum miR30 levels in patients with gastric cancer were not related to sex， age， depth of infiltration and Lauren classification， but related to lymph node metastasis， tumor size， TNM staging and degree of differentiation （P＜005）. The low expression rates of patients with lymph node metastasis， tumor size more than 5 cm， TNM ⅢⅣ and low differentiation were 632％ （48／76）， 726％ （45／62）， 923％ （36／39） and 681％ （32／47）， higher than 375％ （12／32）， 326％ （15／46）， 348％ （24／69） and 459％ （28／61） of lymph nodes without metastasis， tumor size＜5 cm， TNM ⅠⅡ and middlehigh differentiation （P＜005）. The median overall survival of miR30 lowexpression group was 230 months， shorter than 360 months of highexpression group （P＜005）. 
ConclusionMiR30 is lowly expressed in the serum of patients with gastric cancer， and is involved in the development of gastric cancer and the prognosis of patients with low serum miR30 level is poor. It has the potential as a molecular screening and prognostic marker for gastric cancer.

Key words: Gastric cancer, MicroRNA30, Clinical significance, Prognosis