Unique variants of hCG in sera of choriocarcinoma patients.

Human chorionic gonadotropin (hCG) of pregnancy can be separated into several variants by an isoelectric focusing (IEF) method. The hCG produced by choriocarcinoma consists of components found in pregnancy sera (pI 3.9-6.0) and, in addition, unique variants with more acidic isoelectric points ranging from 3.2 to 3.7. The sera of all five patients with advanced choriocarcinoma contained these unique acidic variants of hCG and the immunoreactive levels were significantly higher in these patients than in normal pregnant women or patients afflicted with hydatidiform mole or invasive mole. When the acidic variants of hCG were treated with neuraminidase they migrated to the alkaline region (pI 9-11) of the IEF column. In conclusion, sera of choriocarcinoma patients contain unique variants of hCG. The finding that these highly acidic components can be converted to molecules with an alkaline pI by neuraminidase digestion suggests that this high negative charge may be due to an increased sialic acid content. Patients possessing the acidic variants of hCG in their sera had poor survival rate. Determination of the variants may be useful as a prognosis marker and in evaluating the efficacy of therapy.