Evaluating human choriogonadotropin heterogeneity in nongestational malignancy with monoclonal immunoassays.

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