Expression and clinicopathologic significance of glypican 3 in hepatocellular carcinoma

Abstract

Glypican 3 (GPC3) is a glycosylphosphatidylinositol-anchored membrane protein and plays an important role in regulation of cell growth, differentiation, and migration. The aims of this study were to investigate the expression of GPC3 in human liver, biliary tract, and pancreatic tumors and to evaluate its diagnostic role in differentiating hepatocellular carcinoma (HCC) from other hepatic mimickers. Immunohistochemistry was performed on a large collection of surgically resected samples from 941 primary liver tumors, 50 metastatic adenocarcinomas, and 30 normal livers as well as primary adenocarcinomas of the pancreas (n = 17), gallbladder (n = 30), and extrahepatic bile duct (n = 20). The relationship of GPC3 expression and clinicopathologic features in patients with HCC was determined. We found that 516 (52%) of the 991 liver neoplastic tissue samples demonstrated positive staining for GPC3. A high incidence of GPC3 expression (492/757; 65%) was observed in HCC, whereas intrahepatic cholangiocarcinomas, adenocarcinomas, and benign liver lesions displayed rare positive cases. There were significant correlations between GPC3 expression and clinicopathologic characteristics, including histologic grade (P < .001), intrahepatic metastasis (P = .007), and positive serum hepatitis B surface antigen (P = .042), in patients with HCC. In conclusion, our results confirm the high expression of GPC3 in HCC and suggest its potential diagnostic value as a clinical marker for this disease.

Introduction

Glypicans are a family of heparan sulfate proteoglycans that are bound to the outer surface of the plasma membrane by a glycosylphosphatidylinositol anchor [1]. They regulate several signaling pathways, involving Wnts, Hedgehogs, fibroblast growth factors, and bone morphogenetic proteins [2]. Glypicans are expressed predominantly during development and have a cell- and tissue-specific pattern [1], [2], [3]. Up to now, there are 6 glypican family members identified in mammals, namely, glypican-1 to glypican-6. The gene encoding glypican 3 (GPC3), located on Xq26, is of particular interest. Several studies have underlined an important role of GPC3 in regulation of cell growth, differentiation, and migration [1]. Normally, GPC3 is expressed in fetal tissues and trophoblastic cells and has little or no expression in adult tissues except for normal ovarian, mammary, and mesothelial tissues [4]. Down-regulation of GPC3 is frequently detected in ovarian carcinoma, breast cancer, and mesothelioma [4], implying GPC3 as a tumor suppressor gene in these organs. In contrast, GPC3 may act as an oncofetal protein in carcinomas of various other organs, such as hepatocellular carcinoma (HCC) [5], [6], [7], [8], [9], fibrolamellar carcinoma [10], germ tumor [11], lung squamous cell carcinoma [12], and gastric cancer [13], as this gene is highly expressed in the tumor lesions compared with corresponding normal tissues.

One of the challenges in histopathologic diagnosis of hepatic mass lesions is to distinguish HCC (particularly well differentiated) from hepatocellular adenoma. The available immunomarkers, such as α-fetoprotein (AFP), polyclonal carcinoembryonic antigen, and CD34, have significant diagnostic limitations in clinical practice [14]. Previously, data have demonstrated a high incidence of GPC3 expression (>64%) in HCC and suggested its implications in detecting malignant hepatic lesions [5], [6], [7], [8], [9], [14], [15]. The combined use of serum GPC3 and AFP provides a potentially promising tool to better differentiate HCC from benign liver disorders as well as from other liver cancers [16]. However, GPC3 expression can also be detected in a variable percentage of benign regenerative nodules and high-grade dysplastic nodules [5], [6], [9], [14], [17]. In the present study, we aimed to investigate GPC3 expression in human liver, biliary tract, and pancreatic tumors and to evaluate its diagnostic potentials in differentiating HCC from other hepatic mimickers.