AFP-producing gastric cancer and hepatocellular carcinoma with discrepancies in AFP-L3 expression

Alpha-fetoprotein (AFP) is widely used as a tumor biomarker in the diagnosis and surveillance of hepatocellular carcinoma (HCC). AFP is a glycoprotein bearing N-linked glycans, and can be classified into three glycoforms: AFP-L1, AFP-L2, and AFP-L3. AFP-L3, the α(1,6)-fucosylated isoform, is regarded as a highly specific biomarker for HCC and is often associated with aggressive tumor biology. In contrast, AFP-producing gastric carcinoma (AFPGC) is rare, and few studies have examined the relationship between AFP-L3 and AFPGC. Here, we present a case who developed AFP-positive HCC without AFP-L3 elevation, and subsequently AFPGC showing marked elevation of the AFP-L3 fraction. This demonstrates that AFP-L3 elevation is not entirely specific to HCC and may also be observed in AFPGC. Furthermore, this case highlights that fucosylation activity may differ among AFP-producing tumors arising in different organs within the same individual.