Immunohistochemical expression of SALL4 in hepatocellular carcinoma, a potential pitfall in the differential diagnosis of yolk sac tumors

SALL4 is a transcription factor that serves as a marker of yolk sac tumor. Yolk sac tumor and hepatocellular carcinoma share histologic, serologic, and immunohistochemical features. Previous studies have shown lack of SALL4 expression in hepatocellular carcinoma, suggesting utility in this differential diagnosis. Sixty-nine samples of hepatocellular carcinoma were retrieved from surgical pathology archives and used to construct 9 tissue microarrays. A germ cell tumor tissue microarray containing 10 yolk sac tumors was used for comparison. Extent, intensity, and pattern of nuclear SALL4 expression were assessed in each spot. Mean percentage of expression was calculated for each tumor and used during analysis. Optimal discriminatory extent of expression cutoff was determined by receiver operating characteristic curve analysis. Other potential discriminatory markers including Hep Par1 were also evaluated. Forty-six percent (32/69) of hepatocellular carcinoma and all yolk sac tumors revealed at least focal expression of SALL4. A unique punctuate/clumped pattern of nuclear staining was present in 94% (30/32) of hepatocellular carcinoma, whereas all yolk sac tumors displayed a diffuse finely granular nuclear staining pattern. A 25% extent of SALL4 expression cutoff was found to be optimal for the distinction of yolk sac tumor from hepatocellular carcinoma yielding a sensitivity of 100%, specificity of 92.8%, and a positive predictive value of 66.6% for yolk sac tumor diagnosis. The addition of Hep Par1 increased the specificity (99%) and positive predictive value (90%). This is the first report of SALL4 expression in hepatocellular carcinoma. Our finding should be taken into consideration in the differential diagnosis of hepatocellular carcinoma and yolk sac tumor. The unique punctuate/clumped pattern seen in hepatocellular carcinoma cases could be of further discriminatory value.