Hepatic biliary adenofibroma (BAF) is a rare benign bile duct neoplasm that has garnered increasing attention due to its potential role as a precursor lesion for intrahepatic cholangiocarcinoma (iCCA). Although it shares histopathological features with other biliary tumors, BAF is distinct in its composition, consisting of low-grade tubuloglandular and microcystic bile duct structures embedded in a dense fibrous stroma. Despite its classification as a benign tumor, emerging case reports suggest that BAF may undergo malignant transformation. However, its rarity and limited molecular characterization contribute to diagnostic uncertainties. This review consolidates the current understanding of BAF's histopathological and molecular characteristics, highlights its diagnostic challenges, explores its potential for malignant transformation, and outlines future research directions.
Clinicopathologic Characteristics
Since its first description by Tsui et al. in 1993, fewer than 25 cases of BAF have been documented in the English literature. BAF typically presents as a well-circumscribed mass in the liver, often measuring between 1.7 cm and 16 cm. Histologically, it features biliary tubules, acini, and microcysts, resembling von Meyenburg complexes (VMC) but with a larger size and occasional nuclear atypia. Immunohistochemical staining shows positivity for markers such as CK7, CK19, and EMA, indicative of a biliary epithelial phenotype. While most reported cases have followed an indolent clinical course after surgical excision, some reports suggest a possible transition to iCCA, raising concerns about its malignant potential.
BAF with Malignant Transformation
The potential for BAF to transform into iCCA remains a subject of debate. Some reported cases describe dysplastic changes in BAF, with histological features suggestive of malignant progression. However, inconsistencies in the histopathological confirmation of these cases cast doubt on some claims of transformation. Several studies suggest that BAF may exist on a spectrum with iCCA, particularly given findings of chromosomal copy number alterations in some cases. Notably, an estimated 37% of reported BAF cases have demonstrated malignant transformation, though the true risk remains unclear due to limited case numbers.
Differential Diagnosis
BAF must be distinguished from other biliary lesions, including von Meyenburg complexes, bile duct adenomas (BDA), and intrahepatic cholangiocarcinoma. VMC is a miniature version of BAF, typically under 0.5 cm in size, and is considered a developmental anomaly. BDA is a well-circumscribed lesion smaller than BAF and is characterized by evenly spaced bile duct structures without the cystic dilation seen in BAF. iCCA, on the other hand, can present with a similar tubuloglandular and microcystic pattern, making differentiation from BAF challenging, particularly on biopsy specimens. The recently proposed "tubulocystic carcinoma" subtype of iCCA shares some morphologic overlap with BAF, further complicating the diagnostic process.
Molecular Pathogenesis
Molecular studies on BAF remain limited, but available data suggest that it exhibits distinct genetic alterations from iCCA. Most BAF cases demonstrate a wild-type p53 expression pattern, suggesting an absence of TP53 mutations, which are frequently observed in iCCA. However, some cases of BAF with malignant transformation have shown amplifications of CCND1 and ERBB2, as well as NRAS mutations, indicating potential oncogenic progression. In contrast, iCCA exhibits a diverse molecular landscape with frequent alterations in TP53, ARID1A, IDH1/2, and FGFR2 fusions, among others. The molecular similarities and differences between BAF and iCCA warrant further investigation to clarify the neoplastic potential of BAF.
Future Directions
Given the rarity of BAF, several key questions remain unanswered. First, further studies are needed to establish a clear histopathological distinction between BAF and related entities such as VMC and bile duct adenomas. Second, molecular characterization of BAF and its potential for malignant transformation should be prioritized. Future research should focus on identifying reliable biomarkers for distinguishing BAF from iCCA and determining whether regular surveillance is necessary for patients with diagnosed BAF. Additionally, large-scale studies are needed to assess the true incidence of BAF and its clinical significance.
Conclusions
Hepatic biliary adenofibroma is an enigmatic entity that poses diagnostic challenges due to its histological overlap with other biliary tumors and its potential for malignant transformation. While currently recognized as a benign neoplasm, its emerging association with iCCA necessitates a cautious approach to diagnosis and management. Given the limited number of reported cases, further research is essential to elucidate its molecular underpinnings, refine diagnostic criteria, and determine its true clinical behavior. Until then, thorough histological examination and complete surgical excision remain the best approaches for managing BAF.
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The study was recently published in the Journal of Clinical and Translational Pathology .
Journal of Clinical and Translational Pathology (JCTP) is the official scientific journal of the Chinese American Pathologists Association (CAPA). It publishes high quality peer-reviewed original research, reviews, perspectives, commentaries, and letters that are pertinent to clinical and translational pathology, including but not limited to anatomic pathology and clinical pathology. Basic scientific research on pathogenesis of diseases as well as application of pathology-related diagnostic techniques or methodologies also fit the scope of the JCTP.
