Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver accounting for an estimated 70%-85% of total liver cancers worldwide.1,2 While the highest liver cancer rates are found in East and Southeast Asia and sub-Saharan Africa, the incidence is increasing in the West due to the burden of chronic hepatitis C infection and steatohepatitis attributed to the obesity epidemic.1,3 Although advancements in diagnostic imaging modalities and refined methods of clinical investigation have obviated the need for tissue diagnosis in some cases,4,5 fine needle aspiration (FNA) biopsy remains the procedure of choice in the assessment and diagnosis of focal liver nodules and masses.2 Unfortunately, diagnostic pitfalls exist in the cytologic distinction of HCC from other hepatocellular and non-hepatocellular mass lesions. Of note, the cytologic distinction of regenerative cirrhotic nodules, hepatic adenoma, and focal nodular hyperplasia from well-differentiated HCC presents a diagnostic challenge, particularly in small FNA biopsies with limited sampling. Similarly, cases of metastatic carcinoma and other benign and malignant non-hepatocellular mimics are well documented and can be problematic.4-7 In difficult or equivocal cases, the application of immunohistochemical (IHC) panels has been shown to aid in the distinction of benign and malignant liver lesions.4-9 In particular, the application of CD10, polyclonal carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), Hep-Par1, and glypican-3 (GPC-3) IHC has proven valuable in liver biopsy and FNA cytology specimens.5-10 IHC staining for Hep-Par1, a mitochondrial urea cycle antigen, has demonstrated high sensitivity and specificity in the distinction between metastatic carcinoma and HCC but is also expressed in benign hepatocellular lesions.8,9
In contrast, GPC-3, a heparin sulphate proteoglycan expressed at high levels in HCC, has shown high specificity with suboptimal sensitivity in the diagnosis of HCC when used in isolation. Arginase-1 is a key urea cycle metalloenzyme that has recently demonstrated an expression in normal human liver with a high degree of specificity and specifically, arginase-1 has been shown by immunohistochemistry to be concentrated in periportal hepatocytes.11,12 In sections of normal liver, anti-arginase-1 produced strong, diffuse cytoplasmic reactivity in all hepatocytes throughout the lobule. In a few cases, patchy nuclear reactivity was also evident in hepatocytes along with the strong cytoplasmic reactivity. There was no reactivity in bile duct epithelial cells, sinusoidal endothelial cells, Kupffer cells, or vascular endothelial cells. Only HCCs showing cytoplasmic or cytoplasmic plus nuclear reactivity were considered to be positive for anti-arginase-1.
Recent studies have shown the usefulness of anti-arginase-1 as an IHC marker of hepatocellular differentiation in benign and malignant lesions of liver on biopsy as well as fine needle aspiration specimens.13,14 Arginase-1 expression was present in all (100%) of well-differentiated HCC, 96% cases of moderately differentiated HCC and was present in 85% of cases of poorly differentiated HCC. Similarly, Hep-Par1 expression was noted in all (100%) of well-differentiated HCC; however, Hep-Par1 expression was only noted in 83% moderately differentiated HCC cases and 50% poorly differentiated HCC. In contrast, GPC-3 expression was only observed in 0–23% of well differentiated HCC with staining observed in 60% and 40–50% of moderately differentiated and poorly differentiated HCC, respectively. Therefore, anti-arginase-1 may be of use to distinguish between a poorly differentiated HCC and an adenocarcinoma although it would not be useful in distinguishing between a hepatic adenoma and a well-differentiated HCC, which would require a panel of antibodies to solve the associated diagnostic problem.13,14
Anti-arginase-1 is more specific than antibodies against Hep-Par1 and glypican-3 in diagnosing hepatocellular carcinoma. Anti-Hep-Par1 is occasionally strongly positive in carcinomas of other anatomic sites, such as GI and lung, whereas anti-arginase-1 is negative in these sites. Anti-glypican-3 has been found to be positive in germ cell tumors, such as yolk sac tumor and choriocarcinoma.13,15
Research & Development at Cell Marque:
We have evaluated this rabbit monoclonal IgG antibody against arginase-1 by using normal tissues with different buffers, reaction conditions and dilutions.
As shown in the Fig. 1, anti-arginase-1 strongly stains malignant cells of hepatocellular carcinoma. Fig. 2 demonstrates that anti-arginase-1 highlights normal liver whereas normal kidney is negative for arginase-1. Fig. 3 displays no staining in breast invasive ductal carcinoma. Fig. 4 metastatic colonic carcinoma shows negative staining for arginase-1.
The investigation leads us to make the following recommendations:
Conclusion of Technical Investigation:
Anti-arginase-1 antibody is a very helpful antibody. In a panel with antibodies against S100P, CK7, CK20, and CDX-2 it can be used for differential diagnosis in hepatocellular carcinoma, pancreatic ductal adenocarcinoma, and colorectal carcinoma. When paneled with antibodies against PAX-8 and PAX-2, anti-arginase-1 can be used for differentiation between metastatic renal cell carcinoma and hepatocellular carcinoma. When anti-arginase-1 is coupled with antibodies against Hep-Par1 and Glypican-3, it can increase the sensitivity and specificity for a diagnosis of hepatocellular carcinoma.