Correlation And Clinical Significance Of MSI And KRAS, NRAS Gene Mutations In Colorectal Cancer

Objective:By detecting microsatellite instability(MSI)and KRAS,NRAS gene mutations in colorectal cancer(CRC),to investigate the correlation and clinical significance between MSI and KRAS,NRAS gene mutations in CRC.Methods:Immunohistochemistry(IHC)was used to detect the expression of four mismatch repair(MMR)proteins in 210 cases of CRC,and fluorescence multiplex PCR-capillary electrophoresis was used to detect the distribution of MSI.The mutations of KRAS and NRAS genes in CRC patients were detected by amplification refractory mutation system(ARMS)-fluorescent PCR.Results:(1)The relationship between the expression of MMR protein and the clinicopathological characteristics of CRC: The MMR protein expression total deletion rate was 9.5%(20/210),and the expression deletion rates of MLH1,PMS2,MSH2 and MSH6 were 6.7%(14/210),6.2%(13/210),1%(2/210)and 1.9%(4/210),respectively.Among them,the common expression deletion types MLH1-PMS2 was 4.3%(9/210)and MSH2-MSH6 was 1%(2/210).MSI was associated with age,tumor location and pathological stage(P<0.05),but not with gender,differentiation degree,infiltration depth and distant metastasis(P> 0.05).(2)Consistency analysis between IHC and fluorescence multiplex PCR-capillary electrophoresis: The expression of MMR protein in CRC was highly consistent with MSI typing,and the coincidence rate of the two methods was 96.2%(Kappa=0.778).(3)The relationship between KRAS and NRAS gene mutations and the clinicopathological characteristics of CRC: The total mutation rate of KRAS in CRC was 46.7%(98/210),of which exon 2 was the most common mutation,the mutation rate was 42.9%(90/210),exon 3 and exon 4 were 1.9%(4/210)and 2.4%(5/210),respectively.KRAS gene mutation was correlated with gender,pathological stage and distant metastasis,with statistical significance(P<0.05),but not with age,tumor location,differentiation degree and infiltration depth(P>0.05).The mutation rate of NRAS gene in CRC was 2.9%(6/210),of which exon 2 was 0.5%(1/210)and exon 3 was 2.4%(5/210).The mutation of NRAS gene was not correlated with clinicopathological features,and the difference was not statistically significant(P>0.05).(4)The correlation between KRAS and NRAS gene mutation and MSI: The mutation rate of KRAS gene in MSS CRC was 48.9%(93/190)higher than 25%(5/20)of MSI CRC,and MSI was negatively correlated with KRAS gene mutation(rs=-0.141).The mutation rate of NRAS gene in MSS CRC was 2.9%(6/210),higher than 0%(0/39)of MSI CRC,but there was no significant difference(P>0.05).(5)Univariate survival analysis showed that pathological stage,distant metastasis and KRAS gene mutation were the poor prognostic factors of CRC(P<0.05).Multivariate analysis of COX proportional hazard regression models for meaningful single factors showed that distant metastasis and KRAS gene mutation are risk factors independent of other factors affecting prognosis of CRC patients.Conclusion:(1)MSI is more likely to occur in CRC patients with less than 50 years of age,right colon and low pathological stage.(2)IHC detection of MMR protein screening MSI and luorescence multiplex PCR-capillary electrophoresis MSI classification has a high consistency,for the clinical CRC molecular typing has a higher reliability.(3)KRAS gene mutation is more likely to occur in CRC patients with females,high pathological stage and distant metastasis.(4)MSI was negatively correlated with KRAS gene mutation.(5)KRAS gene mutation is an independent prognostic risk factors for CRC.CRC with KRAS gene mutation is more malignant and prone to distant metastasis.