Immunoglobulin binding factor: a new tumor marker for prostatic tumors.

Human seminal plasma contains an immunoglobulin gamma binding factor (IgBF) with an estimated molecular weight of 16 kD under reducing condition. IgBF was detected only in the prostate, including benign prostatic hypertrophy (BPH) and neoplasm. The present study was performed to determine whether IgBF is a useful prostatic marker. Serum IgBF levels were measured in patients with prostatic tumors and in control patients without tumor by radioimmunoassay. Serum prostatic-specific antigen (PSA), the standard prostatic marker, was also determined. Serum IgBF levels in patients with prostate cancer were significantly higher than those in age-matched controls (P < 0.05). Also, patients with BPH tended to have elevated IgBF levels than the controls, although the values were not statistically significant. In control patients, serum IgBF levels increased with advancing age. There was no correlation between serum levels of IgBF and PSA in patients with prostate cancer. Using cut-off level at 28.5 ng/ml (2 S.D. above the mean IgBF level of age-matched control), the sensitivities were 41.2% (7/17) for prostate cancer, 23.1% (6/26) for BPH, and 5.6% (1/18) for control patients. In conclusion, serum IgBF is a useful marker in the diagnosis of patients with prostatic tumor, and in evaluating the course of treatment.