Elevated serum acid phosphatase levels with rectal carcinoid tumor.

A case of rectal carcinoid tumor with liver metastases is reported in which a markedly elevated serum acid phosphatase level was found. Tissue assays of the patient's tumor, liver metastasis, and uninvolved liver were performed which demonstrated very high tumor levels of acid phosphatase. The patient also had elevated plasma serotonin levels and urinary 5-hydroxyindole acetic acid levels and did not exhibit the carcinoid syndrome. Autopsy showed no prostate cancer or metastatic bone lesions. Serum acid phosphatase elevation may occur with carcinoid lesions of the rectum.