Common and epithelioid variants of hepatic angiomyolipoma exhibit clonal growth and share a distinctive immunophenotype.

Angiomyolipoma represents a rare liver tumor of uncertain histogenesis that is commonly considered a hamartoma. A series of 12 hepatic angiomyolipomas, including 3 samples of the epithelioid subtype, was analyzed for clonality using the human androgen receptor gene locus (HUMARA). Four of 6 informative cases revealed monoclonality. The polyclonal pattern in the 2 remaining cases was most probably caused by excessive infiltration of inflammatory cells. Monoclonality with an identical X-chromosomal inactivation pattern in all nodules was found in a multifocal recurrent tumor indicating a metastatic process. Despite the morphologic heterogeneity, all tumors displayed an identical immunohistochemical labeling pattern. It is concluded that different subtypes of hepatic angiomyolipoma exhibit a monoclonal and hence probably neoplastic growth and share an identical immunophenotype suitable for their identification even in small biopsy specimens. The epithelioid subtype may give rise to intrahepatic metastasis.