Malignant transformation of biliary adenofibroma: a rare biliary cystic tumor.

Biliary adenofibromas (BAFs) are rare, benign biliary cystic tumors with potential for malignant transformation. Of the eleven prior cases of BAF reported in the literature, six showed evidence of malignant transformation. We describe the clinical, imaging and pathology features of two cases of malignant BAF and review the existing literature to raise awareness of this entity and provide additional tools for diagnosing this rare tumor Additionally, we identified a loss of function mutation in the cyclin-dependent kinase inhibitor 2A (CDKN2A) tumor suppressor gene in a malignant caudate lobe BAF, thereby providing potential insight into the molecular pathogenesis of BAF malignant transformation. Although additional cases and longer-term follow-up are needed, our cases suggest that recurrence or metastasis of malignant BAF is not common and that complete surgical resection can be curative.