Intrahepatic cholangiocarcinoma is a complex disease with three different histologic subtypes, the large duct, small duct, and bile ductular types. In the present study, we elucidated whether the three histological subtypes have differences in their methylation profiles and developed a DNA methylation marker that might help identify a subset of ICC with a different prognosis. We screened 113 promoter CpG island loci against 10 cases of intrahepatic cholangiocarcinoma and normal cystic ducts using the MethyLight assay and selected 30 CpG island loci with cancer-associated hypermethylation. Then, we analyzed 172 intrahepatic cholangiocarcinomas for the methylation state at these 30 loci. Six loci, including DLEC1, were more frequently methylated in the bile ductular type and small duct type, whereas six loci were more frequently methylated in the large duct type. Of these 30 loci, DLEC1 methylation was found mainly in the bile ductular type and small duct type but rarely in the large duct type. DLEC1 methylation was significantly associated with a better clinical outcome in intrahepatic cholangiocarcinomas of the small duct type but not of the bile ductular type. DLEC1 methylation was an independent prognostic variable in both cancer-specific survival and recurrence-free survival. For patients with intrahepatic cholangiocarcinoma of the small duct type (n = 68), DLEC1 methylation was found in 26 (38.2%) and was associated with a better clinical outcome for both cancer-specific survival and recurrence-free survival. Our findings suggest that DLEC1 methylation can be utilized to identify a subset with a better prognosis in intrahepatic cholangiocarcinomas of the small duct type.
Keywords: Biomarker; CpG island; DLEC1; Histologic type; Intrahepatic cholangiocarcinoma; Methylation; Prognosis.