Diagnostic evaluation of alanine aminopeptidase as serum marker for detecting cancer.

Alanine aminopeptidase (AAP), carcinoembryonic antigen (CEA), and tissue polypeptide antigen (TPA) were measured in 40 patients with breast and thyroid cancer and in 40 patients suffering from benign tumors and benign noninflammatory diseases. AAP activity was significantly increased (P < 0.001) in all cancer patients considered together. TPA shows a remarkable diagnostic sensitivity but a low specificity. For CEA an inverse situation is observed. Evaluation of the predictive value of the assay of AAP revealed a sufficient sensitivity, a good specificity, a sufficient predictive value of both positive and negative results, and a good efficiency. We believe that the test, if supported by other information, can be useful in the diagnosis of breast and thyroid cancer.