Assessment of the beneficial loci and prognostic implications of microsatellite instability in gastric carcinoma

Microsatellite instability (MSI) is a hyper-mutable phenotype caused by the loss of DNA mismatch repair activity, and plays a crucial role in gastric carcinogenesis. To clarify the role of genetic instability in relation to clinicopathological variables, and to identify predictive MSI markers that facilitate the early detection and improve the classification of gastric carcinomas (GCs), 13 microsatellite (MS) loci, including the National Cancer Institute (NCI) panel of MS markers (D2S123, D5S346, D17S250, BAT25 and BAT26) and 8 dinucleotide repeats (D3S1260, D5S107, D5S409, D17S261, D17S520, D17S855, D18S34 and D18S61) were studied in GC patients. MSI was found in 88.2% (30/34) of GC cases and the number of high-frequency MSI (MSI-H, 23.5%, 8/34), low-frequency MSI (64.7%, 22/34), and stable MSI (11.8%, 4/34), was calculated. Among the MS loci analyzed, D18S34 and D17S261 (15/34, 44.1%) exhibited the highest frequency of MSI, followed by D2S123 (14/34, 41.2%), D5S107, D5S346, D5S409 and D18S61 (12/34, 35.3%) (MSI>35%). MSI-H was particularly prevalent in older patients and was mainly found in the antrum and poorly differentiated tumors. Furthermore, MSI-H was significantly associated with lymph node involvement cases in females. One notable finding in this analysis was that the markers, D17S250 and D17S520, exhibited a significantly higher percentage of MSI in advanced gastric carcinomas than in early gastric carcinomas (P=0.046 and 0.046, respectively), and the D17S520 and BAT26 loci represented significant different correlations between the tumor stages (P=0.038 and 0.042, respectively). This study indicates that the novel markers, D18S34 and D17S261, perform more favorably than the NCI panel for the detection of MSI, and the D17S520 locus presents a potential target for predicting the clinical impact of GC. These novel MS loci may prove to be beneficial and independent tools for the construction of a comprehensive genetic classification for GC cases.