The Clinical And Prognostic Implication Of The Most Frequent Mutations In Histological Subtypes Of Intrahepatic Cholangiocarcinoma

Background and objective: Intrahepatic cholangiocarcinoma(ICC)is the second most frequent primary hepatic malignant tumor after hepatocellular carcinoma with a high degree of malignancy.Furthermore,its incidence is increasing in the last three decades.ICC is related to a dismal prognosis with a postoperative 5-year overall survival rates of 17%.ICCs are much heterogeneous and can arise any point of the intrahepatic biliary tree.Accordingly,ICCs can be histologically classified into two subtypes: large-duct type and small-duct type.Small-duct type may originate from small intrahepatic bile ducts,progenitor cells or mature hepatocytes,presenting as a small-sized tubular or acinar component.Mucin can be rarely detected in cytoplasm or glandular space.The large-duct type arises from large intrahepatic bile ducts or associated peribiliary glands,and is made up of mucin-producing columnar tumor cells arranged in a large-sized glandular or tubular pattern.With the application of next-generation sequencing technology,many frequent genetic mutations have been discovered in ICC,such as isocitrate dehydrogenase 1/2(IDH1/2),BAP1,ARID1 A and PBRM1,with their mutation rates are more than 10%.Although previous studies have researched the association of these mutations with prognosis and clinical features in ICC patients,the data are conflicting.Here we investigated the mutational status of IDH1/2,BAP1,ARID1 A and PBRM1,and determined whether these mutations are correlated to clinicopathological characteristics and prognoses in each histological subtype of ICCs.Due to the heterogeneity of ICC,by analyzing their relationships in the subtypes,rather than the total cohort of ICC,we could obtain more reasonable and accurate results to explain the inconsistencies reported previously.Methods: We collected clinical data,follow-up data and tumor specimens of 130 ICC patients who underwent surgical treatment at Tianjin Medical University Cancer Institute and Hospital from January 2012 to December 2017.The IDH1/2 mutation and loss of BAP1,ARID1 A and PBRM1 expressions were detected by DNA sequencing or immunohistochemical methods,and histological subtype of ICC was determined by hematoxylin-eosin,Alcian blue and S100 P staining.The above data were aggregated into database.Disease-free survival(DFS)and overall survival(OS)were calculated by Kaplan-Meier method,and assessed by log-rank test for survival analysis.Cox proportional hazards model was conducted to analyze prognostic value of gene mutations and other clinical factors.Clinical factors were presented as categorical variables and evaluated by chi-square test or Fisher exact test,as appropriate.In addition,the Kappa value was calculated for the consistency check of IDH1/2 mutation detection by immunohistochemistry and DNA sequencing.Results:(1)DNA sequencing showed 21 ICC patients(16.1%)harbored IDH1/2mutation,and IDH1/2 mutant was detected in 14 cases(10.8%)by Ms Mab-1.There was high consistency between Ms Mab-1 and DNA sequencing in detecting IDH1/2mutation(κ=0.691).(2)27 and 103 cases were identified as large-duct and small duct-type ICCs,respectively.Survival analysis showed that compared with large-duct type,small-duct type ICCs had prolonged OS(P=0.035)and a trend toward increased DFS(P=0.066).But the histological subtype was not an independent prognostic factors of ICCs in multivariate analysis(P=0.543).(3)Survival analysis showed IDH1/2 mutation was associated with prolonged DFS(P=0.014)and a trend toward increased OS(P=0.139)in small-duct type ICC.Multivariate analysis confirmed IDH1/2 mutation was a favorable independent predictor of DFS(P=0.022)in patients with small-duct type.Meanwhile,IDH1/2 mutation was associated with shortened INR(P=0.020),reduced TBIL(P=0.039)and higher histological differentiation(P=0.024)in small-duct type ICC.(4)Univariate Cox regression analysis exhibited that BAP1 expression loss was correlated to prolonged DFS(P=0.039)and OS(P=0.056)in large-duct type ICC.And the loss of BAP1 expression was associated with normal liver function,reduced CA242 and higher histological differentiation in large-duct type ICC(P<0.05).Conclusions:(1)IDH1/2 mutation,exclusively detected in small-duct type ICC,is a favorable predictor and may be related to bilirubin and iron metabolism.Accordingly,we suggest that the detection of IDH1/2 mutation is indispensable to determine targeted therapy in small-duct type ICC,while it is not necessary in large-duct type ICC.(2)Ms Mab-1 is a relatively effective antibody against IDH1/2 mutant in ICC,but the multi-specific antibodies covering all hotspot mutations of IDH1/2 need to be constructed and validated effectively in future.(3)Although patients with large-duct type had worse prognosis than those with small-duct type,the histological subtype was not an independent prognostic factors in ICC.(4)BAP1 expression loss was correlated with improved prognosis only in large-duct type ICC.