Monitor of chemotherapy in gestational trophoblastic neoplasm by radioimmunoassay of the beta-subunit of human chorionic gonadotropin.

Radioimmunoassays and bioassays based on the reactions of the native molecule of human chorionic gonadotropin (HCG) fail to differentiate HCG from pituitary luteinizing hormone (LH). An assay based on the beta-subunit of HCG which detects HCG exclusively has been used in our laboratory to monitor patients undergoing chemotherapy for gestational trophoblastic disease (GTD). We have been able to differentiate minimal, persisting tumor activity from normal levels of pituitary gonadotropins and have based therapy on these findings. Alternatively, treatment has been terminated when HCG is no longer detectable in the serum. Tumor activity has been detected in the beta-subunit assay at a time when biologic activity in the urine indicated remission.