Mucinous intrahepatic cholangiocarcinoma: a distinct variant.

Mucinous variant of intrahepatic cholangiocarcinoma (iCC) is rare, and its clinicopathological features and prognosis are far less clear. Six patients who had iCCs with more than 50% of mucinous component and 79 conventional iCCs were included in the study. The mean size of mucinous and conventional iCCs was 6.2 and 6.0 cm, respectively. Most patients (83%) with mucinous iCC presented at T3 stage or above compared with 28% of the conventional group (P < .01). Three patients with mucinous iCC (50%) died within 1 year. The average survival time of patients with mucinous iCCs was significantly reduced compared with that of the conventional group (9 months versus 2 years; P < .001). Immunohistochemistry was performed on 6 mucinous and 12 conventional iCCs with matched age, sex, and stage, which revealed positive immunoreactivity in MUC1 (83% versus 58%), MUC2 (33% versus 17%), MUC5AC (100% versus 42%), MUC6 (50% versus 0), CK7 (83% versus 83%), CK20 (0 versus 17%), CDX2 (17% versus 0), p53 (67% versus 67%), Smad4 (67% versus 58%), and EGFR (83% versus 42%) in mucinous and conventional iCCs, respectively. Molecular studies showed one mucinous iCC with KRAS G12C mutation and no BRAF or IDH1/2 mutations. Mucinous iCC is a unique variant that constitutes 7% of iCCs. It is more immunoreactive for MUC1, MUC2, MUC5AC, and MUC6. Unlike adenocarcinomas of colorectal primary, mucinous iCCs are often CK7+/CK20-/CDX2- and microsatellite stable. Patients with mucinous iCC likely present at advanced stage upon diagnosis with shorter survival time compared with the conventional counterparts.