Detection of prostate-specific antigen coupled to immunoglobulin M in prostate cancer patients

Background: Several reports indicate that the main biomarkers for liver and colorectal cancer circulating in the blood stream associate with immunoglobulin M (IgM) to form stable complexes that show increased diagnostic relevance compared to circulating free biomarkers. Methods: To further investigate the association between cancer biomarkers and IgM, we assessed the presence of prostate-specific antigen (PSA) as IgM complexes in sera of patients with prostate cancer (PC) or benign prostatic hyperplasia (BPH) in comparison with PSA measurements. Results: PSA-IgM levels were significantly elevated in 40% (20/50) and 12% (6/51) of PC and BPH patients, respectively, compared to 22% (11/50) and 29% (15/51) of PSA positive patients in the same groups. Detection of cancer markedly increased from 22 to 60% by co-determination of both markers (30/50 patients). Significantly elevated levels of PSA-IgM were found in 13 out of 30 patients affected by PC with a PSA value between 4 and 10 ng/mL and only in 4 out of 34 BPH patients in the same PSA range. Conclusions: The results are the first evidence of the occurrence of PSA-IgM complexes in patients with prostate cancer. The gain achieved in cancer detection by using the combination of PSA and PSA-IgM suggests that PSA-IgM could be a complementary serological marker of prostate cancer.