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.