The role of a serum DNA-binding protein (64DP) in the diagnosis of malignant neoplasms.

A DNA-binding protein with a molecular weight of 64,000 (64DP) has been found in elevated concentrations in the serum of patients with malignant diseases. 64DP has been found to be different from any previously described tumor markers, such as AFP, CEA, and C3DP. The results obtained with column SDS - polyacrylamide gel electrophoresis are as follows. 64DP is normally present in the serum at the concentration of 48 +/- 26 micrograms/ml (n = 49). The mean value of 64DP in 96 patients with untreated malignant disease was 167 +/- 67 micrograms/ml, whereas in 41 patients with nonneoplastic disease it was 61 +/- 23 micrograms/ml. No organ or tissue specificity seems to be required for malignant neoplasms to result in elevated serum 64DP concentrations. The clinical stage of the disease does no have much effect on the levels of 64DP and, even with histologically proven early lesions, the patients showed elevated levels of serum 64DP. Following successful surgical resection, 64DP tends to fall toward the normal value. Purification of 64DP was performed and its physicochemical properties have been defined. 64DP is a glycoprotein present in the alpha1-globulin fraction and it is rich in leucine, glutamic acid, and aspartic acid in its amino acid composition. More recently, using purified 64DP preparation, a single radial immunodiffusion assay system has been developed. According to the results of this method, the diagnostic accuracy of 64DP appears to be somewhat low and even marginal for certain types of commonly encountered surgical malignancies. Studies concerning the discrepancy between the results obtained by the two assay methods are now in progress.