495 Indolent Hepatic Neoplasm with Mixed Hepatocellular and Cholangiolar Differentiation: A Previously Unrecognized Entity

Introduction/Objective The current classification of biphasic hepatic tumors includes only combined hepatocellular-cholangiocarcinoma. In contrast, indolent or benign biphenotypic hepatic neoplasms remain unrecognized and unclassified. We report a nonmalignant hepatic neoplasm with bland hepatocellular and cholangiolar features and indolent clinical behavior. Methods/Case Report A 37-year-old female with history of adrenal adenoma presented with multiple hepatic lesions with the largest 9.0 cm in left lobe. Left hepatectomy revealed a well-circumscribed mass in a non-cirrhotic liver with positive margin. Histologically, 60% of the tumor showed bland hepatocellular adenomatous proliferation (arginase +, CK7/CK19-) with immunoprofile not consistent with any known subtype of hepatocellular adenoma or carcinoma. The remaining 40% exhibited bland cholangiolar differentiation (CK7/CK19 +, arginase-) in a punctate, interspersed distribution, forming discrete foci with lumen-like structures scattered throughout the neoplastic hepatocellular background. The cholangiolar component lacked mitotic activity, necrosis, or stromal invasion. Molecular testing showed no TERT or KRAS mutations. The patient remains recurrence-free on imaging over three years, with other stable residual liver lesions, supporting an indolent clinical course. Results NA Conclusion This case represents a previously unrecognized benign-appearing biphasic hepatic neoplasm. Recognizing such unclassified indolent tumors is essential to avoid overdiagnosis and overtreatment, and to prompt further study of their biology.