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Table 2. Low level of circulating microRNAs in plasma/serum in gastric cancer
miR Sample Ethnicity Gastric cancer Control Value Ref.
patietns
miR-15a Serum China 118 (with 20 (without P Song et al. 2017 [90]
chemotherapy) chemotherapy)
miR-17 Serum China 40 36 D Zeng et al. 2014 [91]
miR-26a Plasma China 285 285 D Qiu et al. 2016 [92]
miR-31 Serum China 92 89 D Huang et al. 2016 [79]
miR-92a Serum China 92 89 D Huang et al. 2016 [79]
miR-93 Serum China 118 (with 20 (without P Song et al. 2017 [84]
chemotherapy) chemotherapy)
miR-106b Serum China 40 36 D Zeng et al. 2014 [91]
miR-122 Plasma China 96 36 D Chen et al. 2014 [52]
miR-181b Serum China 92 89 D Huang et al. 2016 [79]
miR-195-5p Serum China 62 36 D, P Shen et al. 2016 [93]
Plasma Turkey 20 190 D Gorur et al. 2013 [94]
miR-203 Serum China 92 89 D Huang et al. 2016 [79]
Japan 130 22 P, M Imaoka et al. 2016 [62]
miR-204 Serum China 115 40 P, M Chen et al. 2016 [95]
miR-206 Serum China 150 150 D Hou et al. 2016 [96]
miR-218 Plasma China 70 70 D Li et al. 2012 [75]
Serum China 68 56 P Xin et al. 2014 [97]
miR-375 Serum China NA NA D Zhang et al. 2012 [98]
miR-503 Serum China 68 32 D, P Wu et al. 2016 [99]
miR-940 Plasma China 110 30 D Liu et al. 2016 [56]
let-7a Plasma Japan 69 30 D Tsujiura et al. 2010 [32]
Serum China 80 NA D Wang et al. 2013 [100]
D: diagnostic value; P: prognostic value; M: monitoring value

Regarding tumor-suppressor miRNAs, Imaoka et al. reported that serum expression of miR-203 was
[62]
significantly lower in stage IV than in stages I-III of gastric cancer patients. Serum miR-203 expression
was significantly lower in gastric cancer patients with worse malignant potential, as indicated by higher T
stage, vessel invasion, and nodal, peritoneal, and distant metastases. Low expression of serum miR-203 was
correlated with poor disease-free survival and overall survival. This low expression was an independent
predictive marker for metastases, including nodal, peritoneal, and distant metastases, and a poor prognosis
in gastric cancer patients . Therefore, various downregulated circulating miRNAs have been identified as
[62]
blood-based prognostic biomarkers for gastric cancer: miR-15a, miR-93, miR-195-5p, miR-203, miR-204,
miR-218 and miR-503 [Table 2] [62,84,90,93,95,97,99] .

DIFFERENT EXPRESSION LEVELS OF SOME CIRCULATING MIRNAS BETWEEN PLASMA AND
SERUM IN GASTRIC CANCER
From the viewpoint of liquid biopsy using blood miRNAs, many issues must still be addressed before novel
findings can be translated into clinically useful and noninvasive screening strategies for gastric cancer
patients. Because plasma includes more abundant proteins, such as coagulation factors, than does serum,
miRNA profiles in the plasma of cancer patients differ considerably from those in the serum , as has been
[63]
shown in esophageal cancer [37,64] and pancreatic cancer . In gastric cancer, the expression levels of some
[63]
circulating miRNAs, such as miR-17, miR-92a, miR-93, and miR-106b, moved in opposite directions in the
plasma and serum [Tables 1 and 2]. Although detailed mechanisms remain unknown, the data strongly
suggest that these issues should be considered in future clinical applications of cancer treatments.

FUTURE PERSPECTIVES ON CIRCULATING TUMOR-SUPPRESSOR MICRORNAS FOR TREATMENT

TARGETS IN GASTRIC CANCER
Multiple researchers have recently examined therapeutic miRNA-based drugs by using synthetic miRNA