Unveiling the unexplored secret: Aggressive behavior and poor survival in intrahepatic mucinous adenocarcinoma compared to conventional adenocarcinoma.

Intrahepatic bile duct mucinous adenocarcinoma (IHBDMAC) is a rare pathological subtype of intrahepatic cholangiocarcinoma (IHCC), and its tumor biological features and survival outcomes have rarely been explored, especially when compared to the most common subtype, intrahepatic bile duct adenocarcinoma (IHBDAC). Therefore, the aim of this study was to explore the clinical features and survival outcomes of IHBDAC and IHBDMAC using the Surveillance, Epidemiology, and End Results (SEER) database from 2000 to 2021. A total of 1,126 patients were included, with 1,083 diagnosed with IHBDAC and 43 diagnosed with IHBDMAC. Patients with IHBDMAC presented with a more advanced T stage (55.8% vs. 36.9%, P = 0.012) and higher rate of lymph node metastasis (37.2% vs. 24.9%, P = 0.070). Cox regression identified advanced T stage, lymph node metastasis, and distant metastasis as poor survival predictors, while chemotherapy and surgery were protective factors. Survival analyses revealed significantly worse overall survival (OS) and cancer-specific survival (CSS) for IHBDMAC compared to IHBDAC (P < 0.05). Even after matching, patients with IHBDMAC still had a worse prognosis than those with IHBDAC. These findings highlight the aggressive nature of IHBDMAC and the need for tailored therapeutic strategies. Future research should focus on prospective studies and molecular insights to develop targeted treatments for IHBDMAC.