Genetic heterogeneity of intrahepatic cholangiocarcinoma: Implications for outcome.

595 Background: Intrahepatic cholangiocarcinoma (IHC) is characterized by marked clinical heterogeneity, likely the result of multiple cells of origin and variable driver gene alterations. The hidden-genome classifier is a statistical algorithm that classifies tumors by integrating multi-level genomic features. In this study, we trained the hidden-genome classifier with extrahepatic cholangiocarcinoma (EHC), gallbladder cancer (GBC) and hepatocellular carcinoma (HCC) as extremes of a spectrum to quantify the genetic heterogeneity of IHC with a view toward improved tumor classification. Methods: An IRB approved retrospective review of patients with biopsy confirmed IHC, EHC, GBC and HCC was conducted. All tumors were subjected to MSK-IMPACT to determine the mutational profile. A two-class model was built and internally validated with the genomic data of EHC/GBC as one class and HCC as the other class. IHC tumors were analyzed in the model and classified into three groups based on their proportional genetic resemblance to EHC/GBC (Biliary Class) or HCC (HCC Class), with the remainder as Intermediate Class. The classification thresholds were 90% resemblance to EHC/GBC or HCC and were determined by the inflection point of predicted survival. The survivals of the three groups were analyzed and compared. Results: A total of 1497 patients were included: IHC (733), EHC (208), GBC (258) and HCC (298). 527 IHC tumors with complete metagenetic information were analyzed in the model, showing a continuous spectrum of alterations, ranging from Biliary Class (122 tumors), Intermediate Class (375 tumors) to HCC Class (30 tumor). The biliary-class IHC was characterized by frequent alterations of IDH1 R132C, KRAS, SMAD4, ERBB2 gain, MDM2 gain, and CKDN2A loss, while the HCC-class IHC was primarily characterized by TERT alterations. In patients with unresected IHCs, the median survival ranged from 1 year (CI 0.77, 1.5) in Biliary Class, 1.8 years (CI 1.5, 2.0) in Intermediate Class, to 2 years (CI 0.93, NR) in HCC Class. In patients subjected to resection, the median survival of Biliary Class (2.4 years, CI 2.1, NR) was lower than both the Intermediate Class (5.1 years, CI 4.8, 6.9) and the HCC Class (3.4 years, CI 2.7, NR). Conclusions: By integrating multi-level genomic features, we leveraged the mutational heterogeneity to classify IHC based on its resemblance to EHC/GBC or HCC tumors. We found that the survival in IHC patients appeared to decline with increasing genomic similarity to Biliary Class. The results support a genomic basis for IHC’s variable clinical behavior and point to a role of mutational testing to guide clinical intervention. [Table: see text]