Germ cell tumors express a specific alpha-fetoprotein variant detectable by isoelectric focusing

Many nonseminomatous germ cell tumors (NSGCTs) express elevated levels of serum alpha-fetoprotein (AFP), which is widely used for diagnosis and monitoring therapy. Alpha-fetoprotein is also expressed in patients with hepatocellular carcinoma (HCC). In these sera, several variants, some highly specific, recently have been detected by isoelectric focusing.

Sera were collected from nine patients with NSGCTs, five pregnant women, and five patients with HCC. After isoelectric focusing, the proteins were transferred to nitrocellulose membrane by blotting and incubated with polyclonal rabbit antihuman AFP conjugated with horseradish peroxidase. The enhanced chemiluminescence detection system and Hyperfilm-ECL were used to render the protein bands visible and each was quantified as a percentage of the total AFP using a densitometer.

Isoelectric focusing of serum alpha-fetoprotein from the patients with NSGCTs (four testicular, five mediastinal) revealed a consistent pattern characterized by a specific band (band +III). A second band (band +II) that is also seen in sera from patients with hepatocellular carcinoma was present in all patients. The overall pattern was distinct from that of AFP from HCC and that produced during late pregnancy. The two characteristic bands (AFP +II and +III) were responsible for the great majority of total AFP in these patients; estimation of serial sera in patients undergoing treatment showed that total and "malignant" AFP changed in parallel. Banding patterns, apart from one patient, were identical in patients with testicular and mediastinal NSGCTs.

NSGCTs tumors express a highly consistent and specific pattern of AFP variants. More detailed analysis of AFP patterns in larger numbers of patients may provide further insight into the cellular heterogeneity of germ cell tumors.