| Objective:To study the differences of MRI characteristics of rectal adenocarcinoma with different molecular types,and to explore the feasibility of using MRI to evaluate the molecular classification of rectal cancer before operation.Materials and methods:All 82 patients with rectal adenocarcinoma were examined by 3.0T-MRI before operation.The MRI features of the tumor were observed and some features were extracted: tumor location,gross shape,periintestinal involvement,circumferential incisal margin(circumferential margin,CRM),longitudinal tumor lengths(LTL),axial tumor lengths(ATL),ATL/LTL and average ADC value.Routine HE staining and immunohistochemical staining were performed to record the TMN stage,T stage,N stage,vascular tumor thrombus and nerve infiltration of the tumor,and to detect the expression of Ki-67 and VEGF.Allele specific amplification(PCR)was used to detect the mutations of KRAS gene(exon 2,exon 3,exon 4),NRAS(codon 12,13,61)and BARF(V600E).The stability of microsatellite DNA Bethesda marker sites was detected by capillary electrophoresis gene scanning.The MRI characteristics of rectal cancer with different molecular types were compared and statistically analyzed to explore the ability of various features to predict gene mutation.Results:(1)KRAS gene mutation was detected in 40 of all 82 patients,with a mutation rate of 48.78%(5 cases of 40);NRAS gene mutation and 6.10% mutation rate).Among them,70 cases were tested for BARF gene,2 cases were mutated,and the mutation rate was 2.86%.The results of 72 patients with microsatellite instability showed that 3 cases were microsatellite instability,including 1 case of high frequency instability(MSI-H),2 cases of low frequency instability(MSI-L),and the rest were microsatellite stable MSS.Among the 82 patients,74 cases(90.24%)had Ki-67 index≥ 50%,of which 70 cases were detected for VEGF expression,32 cases were positive,accounting for 45.71%.Statistical analysis showed that there was no significant correlation between KRAS mutation rate,positive rate of VEGF expression and Ki-67 index with age,sex,pathological stage,depth of invasion,lymph node metastasis,vascular tumor thrombus,nerve invasion and other clinicopathological features(P > 0.05).(2)There was a significant correlation between tumor morphology and KRAS mutation rate(χ 2 = 11.815,P < 0.001).The 3 tumors with intraluminal Polypoid growth were all KRAS mutations.The location of the tumor was significantly correlated with the positive expression of VEGF(P=0.011).Of the 32 patients located in the upper segment,only 9(28.13%)were positive for VEGF,while11(73.33%)were positive for VEGF in the 15 patients located in the lower segment.The extent of periintestinal involvement of the tumor was possibly related to the positive expression of Ki-67.The expression of Ki-67 was negative in 8 patients whose lesion range was more than 3 and 4 weeks.(3)There were significant differences in ATL and ATL/LTL between KRAS mutant group and wild type group.The ROC values of the two groups were 0.645 and 0.655,respectively.The sensitivity and specificity of predicting KRAS mutation in rectal cancer with ATL ≥13.5 were 0.525 and 0.786,respectively,and the sensitivity and specificity of predicting KRAS mutation in rectal cancer with ATL/LTL ≥ 0.2595 threshold were0.700 and 0.738,respectively.There was no significant difference in ATL,ATL/LTL,LTL and average ADC values in Ki-67 index and positive expression rate of VEGF in rectal cancer.There was no significant correlation between KRAS mutation rate and Ki-67 index and VEGF expression positive rate.Conclusion:(1)KRAS mutation,Ki-67 index and VEGF positive expression in rectal cancer and their clinicopathological characteristics.There was no correlation between KRAS mutation and Ki-67 index and positive expression of VEGF.(2)MRI characteristic tumor morphology,ATL and ATL/LTL of rectal cancer were significantly different between KRAS mutant group and wild type group.Rectal cancer with Polypoid growth and larger ATL and ATL/LTL were more likely to have KRAS gene mutation,although the overall prediction value was low,indicating that the prediction of MRI characteristics of rectal cancer has a certain significance in KRAS gene mutation. |
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