Urinary Human Chorionic Gonadotropin Free β-Subunit and β-Core Fragment: A New Marker of Gynecological Cancers

Abstract

Many investigators have shown that a small proportion (13–36%) of subjects with nontrophoblastic gynecological cancers have elevated serum levels of human chorionic gonadotropin (hCG). The low proportion with detectable levels and the accompanying low titers have limited the use of hCG as a tumor marker. hCG is a glycoprotein composed of two noncovalently linked subunits (α and β), which are the products of separate genes. With the intent of expanding the use of hCG as a tumor marker we investigated levels of hCG free β-subunit and asialo free β-subunit and its core glycopeptide (composed of β-subunit residues 6–40 disulfide-linked to 55–92), collectively called urinary gonadotropin fragments (UGF), in healthy and cancer patients. An immunoradiometric assay was developed, using the core glycopeptide-directed antibody B204, that similarly measures the hCG free β-subunit and the asialo free β-subunit and its core glycopeptide. Parallel urine and serum samples were collected from 87 women with active gynecological cancer and hCG and UGF were measured. Just 18% of the women tested had detectable serum levels of hCG (>0.2 ng/ml); none had elevated serum levels in the UGF assay (>0.2 ng/ml). Of the same group, 32% had detectable urine hCG levels (mean titer, 0.50 ng/ml) and 74% exhibited elevated urinary levels in the UGF assay (mean titer, 2.0 ng/ml). In a control group (urines from 50 nonpregnant healthy women), 47 negative and three borderline positive results (0.30, 0.35, and 0.48 ng/ml) were observed in the UGF assay. These results suggested a sensitivity of 74% and specificity of 92% for the UGF test for gynecological cancers. By disease, 70% of those with cervical, 73% of those with ovarian, and 77% of those with endometrial cancers had detectable UGF levels (>0.2 ng/ml). By stage, 50, 62, 75, 86, and 100% of those with stage 1, 2, 3, 4, or recurrent disease, respectively, had positive results. UGF is a promising new marker of gynecological malignancies.