Reduced metabolic clearance of acidic variants of human choriogonadotropin from patients with testicular cancer

We investigated the plasma disappearance of purified urinary human choriogonadotropin (hCG) and acidic variants of hCG (AV-hCG) that are excreted in the urine of patients with testicular cancer to determine if there are differences in their disappearance rates. All cancer patients had relatively increased fractions (10% to 46%) of AV-hCG in their serum when compared with hCG from pregnant control subjects (less than 4% present as AV-hCG). After initiation of therapy in 12 patients with nonseminomatous testicular tumors, the proportion of hCG present as acidic variants in serum rose despite lower serum total hCG concentrations. Samples of highly purified AV-hCG (pI, 3.3 to 4.0) obtained from three patients by concentration from urine and isoelectric focusing were evaluated for their disappearance from serum after injection into rats. All AV-hCG samples had decreased clearance rates when compared with that of highly purified hCG (CR123). These data indicate that acidic forms of hCG have a delayed clearance that contributes to the increased proportion of AV-hCG in the serum of patients with hCG-producing neoplasia after therapy.