Evaluation of a new serum testing method for detection of prostate cancer

Purpose: Serum prostate specific antigen is a highly specific test for diseases of the prostate gland but it is not specific for prostate cancer, which can lead to unnecessary biopsies. In an effort to find a more specific test, a new testing method for detecting prostate cancer based on deglycosylation of cell surface proteins and subsequent antibody formation in patients with prostate cancer was evaluated. In addition, antibody generation against the peptide fragments chosen to represent the cell surface proteins was determined to be cancer associated, cancer specific or not related to prostate cancer. Materials and Methods: Antibody titers to 67 unique peptide sequences representing 41 cell surface proteins were determined in 25 men with known prostate cancer (cancer group) and 34 men without prostate cancer (control group). The titers of the control and cancer groups were compared for statistical significance. Additionally, each peptide was identified as being cancer specific, cancer associated or not related to prostate cancer based on whether patients, controls, both or neither had elevated antibody titers. Results: Of the 67 peptides tested 3 demonstrated statistical significance between the control and cancer group titers. Using these 3 informative peptides, 11 of the 25 men known to have prostate cancer had positive results (sensitivity 44%), while 2 of the 34 control patients had positive results (specificity 94%). Of the peptides with significantly different titers in patients and controls 2 of the 19 cell surface proteins known to be present in prostate cancer were represented. No peptides were found to generate antibodies only in patients with cancer (cancer specific), while 3 were cancer associated (increased in cancer and controls). Conclusions: A new approach to testing for prostate cancer, although lacking in sensitivity, appears to be highly specific. The high specificity of this test suggests that when combined with a highly sensitive test, such as prostate specific antigen, screening could be significantly improved.