Evidence for free beta-subunit secretion in so-called human chorionic gonadotropin-positive seminoma.

In 349 patients with pure seminoma the authors determined human chorionic gonadotropin (HCG) plus the free beta-subunit (HCG-beta) by a polyclonal radioimmunoassay (RIA) and found elevated serum levels in 42 patients (12%). In addition, each HCG and HCG-beta were specifically measured by monoclonal immunoradiometric assays (IRMA) in 19 of these patients. Overall 12 patients were HCG-beta positive and 12 HCG positive. Elevated serum levels of both molecules were found in five patients, whereas seven patients showed elevation only in HCG and another seven patients only in HCG-beta. In serum samples of patients with high HCG-beta and minimally elevated HCG levels the free beta-subunit could be detected by gel filtration and immunoradiometric assays, whereas both HCG-beta and holo-HCG were found in ultrafiltered and concentrated urinary samples. The authors conclude that HCG-beta can be present as the major form in serum even if both HCG-beta and HCG are detectable in urine. When measuring hormone concentration as a tumor marker in seminoma patients, methods which determine both activities, HCG plus HCG-beta, seem to be the most reliable. Whereas 16 patients with Stage I-IIc had HCG-beta levels between 0.1 and 2.8 IU/l and currently have no evidence of disease, two patients with Stage IV had HCG-beta levels of 18 and 37 IU/l and died. Current investigations have to clarify the prognostic significance of beta-subunit secretion.