Raised prostate-specific antigen in adenocarcinoma of the colon

Serum prostate-specific antigen (PSA) values above 10 ng/ml are considered highly sensitive and specific for prostatic carcinoma in the absence of prostatic inflammation or trauma. However, in rare instances, non-prostatic malignancies have also been associated with raised serum PSA values. We have encountered a patient with increased serum PSA concentration measured by monoclonal antibody assay who had no evidence of prostatic malignant involvement, but suffered from colon cancer. Before operation for colon cancer his PSA was always over 30 ng/ml on several examinations. After total removal of colon cancer serum PSA level fell down to 1.2 ng/ml. Although immunohistochemical staining of colon cancer with monoclonal PSA antibody was not performed, some relationship between raised PSA and colon cancer is strongly suspected. Substances like serine protease which can cross-react with the PSA antibody might be produced by malignant tumour of non-prostatic origin.