IMMUNOHISTOCHEMICAL STUDY OF HEPATIC ANGIOMYOLIPOMA

An immunohistochemical study was performed on nine hepatic angiomyolip omas (AML) found in eight patients. Histologically, the tumors were fu ndamentally composed of the three heterogeneous tissue components of b lood vessels, smooth muscle cells (SMC), and fat cells, although the p roportions and distributions were quite variable from tumor to tumor a nd from area to area in the same tumor. Additionally, cellular pleomor phism and atypia with occasional bizarre giant cells were found in the SMC component. This histologic feature might lead to a mistaken diagn osis of malignant neoplasm, and pathologists should therefore be aware of the broad histologic spectrum of hepatic AML. However, the immunos taining patterns were basically the same in all nine tumors. All tumor components were negative for epithelial membrane antigen (EMA) and fo r cytokeratin. The spindle-shaped SMC component of the tumor was occas ionally positive for vimentin, desmin and alpha-smooth muscle actin, w hereas epithelioid SMC were negative for all three. Both the epithelio id and spindle-shaped SMC were occasionally positive for S-100 and neu ron-specific enolase. All types of SMC in the tumor, whether spindle, epithelioid, intermediate or pleomorphic SMC, were strongly positive f or HMB-45, a melanoma-specific monoclonal antibody. Fat cells were occ asionally positive for S-100. Endothelial cells were positive for fact or VIII-associated antigen, Among hepatic tumors HMB-45 reactivity is, so far as we know, found exclusively in the SMC of AML, and the HMB-4 5 reactivity of a hepatic tumor is thus clearly an important piece of information in the diagnosis of AML.