Background:
Liver cancer is the second most common cause of cancer-related death worldwide, with hepatocellular carcinoma (HCC) being its predominant tumor type. Alpha fetoprotein (AFP) is the most widely used serum tumor biomarker for the detection of HCC. During embryonal development, the plasma glycoprotein AFP is produced by the yolk salk and the developing liver; by the age of 8 to 12 months, baseline adult levels are reached. Besides HCC, also germ cell tumors of the ovary and testis may produce significant AFP levels. Though the wide clinical use, a systematic clinicopathologic study of AFP immunohistochemistry in HCC together with serum AFP levels has not yet been conducted.
Aim and methods:
In order to assess the prevalence of AFP-expression in HCCs in a large cohort of patients by immunohistochemistry, we established a tissue microarray (TMA) of HCCs of 574 patients that were resected at the University Medical Center Mainz from 1998 to 2017. Spearman's rank correlation coefficient was calculated from preoperative serum AFP levels and AFP immunoreactivity. Kaplan-Meier, Wilcoxon rank-sum test, log rank and univariate Cox's regression analysis were used to determine associations between AFP-expression, serum AFP-levels, patients' survival, etiology of underlying liver disease and other clinical parameters such as liver enzymes.
Results:
Specific AFP immunoreactivity was detected in about 20% of the primary HCCs. About 5% of the HCCs showed strong AFP expression, about 5% intermediate AFP expression and roughly 9% low AFP expression. Serum AFP levels before surgery were available for 172 patients in the same patient cohort. As expected, a moderate correlation of serum AFP levels and AFP immunoreactivity was detected (Spearman's rank correlation coefficient 0.53, p = 1.2e-13). In our cohort, patients with immunohistochemically AFP-positive HCC showed an unfavorable prognosis compared to those without detectable immunoreactivity (HR 1.59; 95% CI, 1.22 – 2.08, p < 0.001). In line with this finding, increased serum AFP levels (15.3≥ng/ml) correlated with decreased survival (HR 1.67; 95% CI, 1.18 – 2.36, p < 0.01). In this line, AFP immunopositivity was significantly associated with vascular invasion and higher tumor grade. There was a trend towards overrepresentation of AFP-negative tumors in patients with non-alcoholic and alcoholic steatohepatitis, and with alcohol consumption, and obese patients significantly more often showed AFP-negative HCCs. We did not detect a significant association of AFP-expression with other parameters (presence or absence of cirrhosis, presence of HBV- or HCV infection, hemochromatosis, primary biliary cholangitis, alpha1-antitrypsin deficiency, as well as with liver enzymes, albumin, CA19 – 9 and urea serum levels).
Conclusion:
AFP expression in HCC, as determined by immunohistochemistry, correlated well with AFP serum levels, and was associated with an unfavorable prognosis. AFP-positive HCCs more often showed vascular invasion and higher tumor grade. Further histopathologic studies are currently undertaken to unravel, whether AFP-positive HCC constitute a clinically relevant subtype of HCC, as proposed for an AFP-positive macrotrabecular HCC subtype by e.g. Okabe and coauthors, PlosOne, 2018.
