Epigenetic upregulation of TET2 is an independent poor prognostic factor for intrahepatic cholangiocarcinoma

Hironori Yamashita,Neil A Youngson,Tomoo Itoh,Masayuki Akita,Shilpa Chokshi,Yoh Zen,Takumi Fukumoto,Tetsuo Ajiki,Aikaterini Tourna

doi:10.1007/s00428-021-03251-x

Abstract

Mutations in IDH1/2 and the epigenetic silencing of TET2 occur in leukaemia or glioma in a mutually exclusive manner. Although intrahepatic cholangiocarcinoma (iCCA) may harbour IDH1/2 mutations, the contribution of TET2 to carcinogenesis remains unknown. In the present study, the expression and promoter methylation of TET2 were investigated in iCCA. The expression of TET2 was assessed in 52 cases of iCCA (small-duct type, n = 33; large-duct type, n = 19) by quantitative PCR, immunohistochemistry (IHC) and a sequencing-based methylation assay, and its relationships with clinicopathological features and alterations in cancer-related genes (e.g., KRAS and IDH1) were investigated. In contrast to non-neoplastic bile ducts, which were negative for TET2 on IHC, 42 cases (81%) of iCCA showed the nuclear overexpression of TET2. Based on IHC scores (area × intensity), these cases were classified as TET2-high (n = 25) and TET2-low (n = 27). The histological type, tumour size, lymph node metastasis and frequency of mutations in cancer-related genes did not significantly differ between the two groups. Overall and recurrence-free survival were significantly worse in patients with TET2-high iCCA than in those with TET2-low iCCA. A multivariate analysis identified the high expression of TET2 as an independent prognostic factor (HR = 2.94; p = 0.007). The degree of methylation at two promoter CpG sites was significantly less in TET2-high iCCA than in TET2-low iCCA or non-cancer tissue. In conclusion, in contrast to other IDH-related neoplasms, TET2 overexpression is common in iCCA of both subtypes, and its high expression, potentially induced by promoter hypomethylation, is an independent poor prognostic factor.

Highlights

Materials and methodsThe findings of recent pathological studies, including ours, suggested a dichotomous classification scheme for intrahepatic cholangiocarcinoma with distinct clinicopathological features [1, 8, 13]
Tumours were larger than 5 cm in 25 cases (48%) and lymph node metastasis was confirmed in 14 cases (27%)
The present study demonstrated that approximately 80% of intrahepatic cholangiocarcinoma (iCCA) cases expressed TET2

Summary

Introduction

Materials and methodsThe findings of recent pathological studies, including ours, suggested a dichotomous classification scheme for intrahepatic cholangiocarcinoma (iCCA) with distinct clinicopathological features [1, 8, 13]. RT-qPCR revealed that the mRNA expression levels of TET2 were significantly higher in iCCA tissue than in background liver/bile duct tissue with a group average Ct difference of 1.5 PCR cycles, equivalent to a 2.8-fold difference (p = 0.004; Fig. 1A). No significant difference was observed in CpG methylation at 8 CpG sites in the promoter of TET2 when all iCCA samples were compared to noncancer tissue (Fig. 1B).

Results

Conclusion