OBJECTIVETo study the role of arginase-1 (Arg-1) expression in differential diagnosis of hepatocellular carcinoma (HCC), Arg-1 staining pattern in clear cell neoplasm (HCC and non-HCC) and Arg-1 expression in non-hepatocellular tumors.

METHODSSeventy-eight cases of HCC (including 8 cases of clear cell type and 70 cases of non- clear cell type) and 246 cases of non-hepatocellular neoplasms (including 29 cases of metastatic tumors such as breast cancer, nasopharyngeal carcinoma and neuroendocrine carcinoma, 77 cases of tumors with clear cell changes such as malignant melanoma, clear cell renal cell carcinoma and alveolar soft part sarcoma, and 140 cases of other types of tumors such as ovarian endometrioid adenocarcinoma, pituitary tumor and thyroid papillary carcinoma) were studied.Immunohistochemical study for Arg-1 was performed on the paraffin-embedded tumor tissue.

RESULTSIn HCC, Arg-1 demonstrated both cytoplasmic and nuclear staining, with an overall sensitivity of 96.2% (75/78).In well, moderately and poorly differentiated HCC, the sensitivity was 15/15, 100% (41/41) and 86.4% (19/22), respectively. That was in contrast to negative staining for Arg-1 in all the 29 cases of metastatic tumors studied. The sensitivity, specificity, positive predictive value and negative predictive value of Arg-1 in distinguishing HCC from metastatic tumors was 96.2%, 100%, 100% and 90.6%, respectively. Cytoplasmic and membranous staining was observed in clear cell type of HCC. The overall sensitivity of Arg-1 expression in the 77 cases of tumors with clear cell changes was 14.3% (11/77), including 8/15 for malignant melanoma, 2/4 for ovarian clear cell carcinoma and 1/1 gall bladder adenocarcinoma with clear cell component.In malignant melanoma and ovarian clear cell carcinoma, only cytoplasmic staining was demonstrated. There was no expression of Arg-1 in the 140 cases of other tumor types studied.

CONCLUSIONSArg-1 is a sensitive and specific marker for HCC.It is a potentially useful immunohistochemical marker in distinguishing HCC from metastatic tumors. Though also expressed in malignant melanoma and ovarian clear cell carcinoma, Arg-1 shows a different staining pattern as compared with that in HCC.