[1666] Immunohistochemical Examination of Arginase-1 Expression in Hepatoblastomas

Jason C Chang, David L Stockman, Sara Szabo. Medical College of Wisconsin, Milwaukee, WI; MD Anderson Cancer Center, Houston, TX; Children's Hospital of Wisconsin, Milwaukee, WI

Background: Hepatoblastomas are the most common pediatric malignant tumors of the liver, typically presenting by the age of 3 years. Histologically, these tumors may be composed of a combination of fetal, embryonal and mesenchymal components; the prognosis is variable, depending on the constituent histologic subtypes. Recently, arginase-1 (Arg-1) has been shown to be a sensitive and specific immunohistochemical marker in hepatocellular carcinomas; however, little is known about its expression in hepatoblastomas. In this study, we investigated the expression of Arg-1 in a large series of hepatoblastomas to assess its utility as a diagnostic marker.
Design: 26 cases of hepatoblastomas were retrieved from the surgical pathology files of a large pediatric hospital. Immunohistochemistry was performed on whole-section slides following antigen retrieval using a polyclonal rabbit antibody to Arg-1 and monoclonal mouse antibody to HepPar-1, and the staining pattern was semi-quantitatively assessed. The extent of immunoreactivity was graded according to the percentage of positive tumor cell, and the intensity of staining was graded as weak, moderate, or strong.
Results: All 26 (100%) cases of hepatoblastomas showed immunoreactivity for Arg-1 with 25/26 (96%) cases showing strong, diffuse positivity. Almost all cases with fetal patterns (24/25, 96%) and all cases with embryonal patterns (17/17, 100%) showed strong, diffuse positivity for Arg-1, whereas mesenchymal patterns seen in 6 cases were completely negative for Arg-1 (0/6, 0%). By comparison, 25/26 (96%) hepatoblastomas were immunoreactive for HepPar-1. Almost all cases with fetal patterns(25/26, 96%) showed strong, diffuse positivity. One case consisting exclusively of fetal pattern was completely negative for HepPar-1. Embryonal patterns tended to show weaker, patchy positivity; the staining for HepPar-1 was only present focally in 3/17 tumors containing embryonal patterns. Similarly, mesenchymal patterns seen in 6 cases were completely negative for HepPar-1 (0/6, 0%).
Conclusions: Our data demonstrated that Arg-1 is a useful marker for hepatoblastomas and shows superior sensitivity compared to HepPar-1. The addition of Arg-1 may aid in the diagnosis of pediatric small round blue cell tumors which have inconclusive immunohistochemical profile, especially on small biopsies and metastases.
Category: Liver

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 116, Wednesday Afternoon


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