Evaluating Human Choriogonadotropin Heterogeneity in Nongestational Malignancy with Monoclonal Immunoassays

The ectopic production of human choriogonadotropin (hCG) and its free α- and β-subunits was evaluated in 195 patients with nongestational malignancy. Dimer hCG was the predominant species secreted. Significant levels of free β-hCG were detected in 11% of patients, and represented 1.6–12% of immunoreactive hCG. In these patients the ratio of free β-subunit to hCG remained constant during their follow-up period. Significant levels of free α-hCG occurred in 1.5% of patients, but were secreted independently of free β-hCG. These findings indicate that immunoassays specific for dimer hCG would not be significantly disadvantaged in monitoring malignancy, and that free β-hCG subunit levels have limited application as a tumor marker.