Prostate-specific acid phosphatase in carcinoid tumors.

Although prostate-specific acid phosphatase (PASP) has been recognized as a specific marker of tissue of prostatic origin, several investigators have pointed out that some of the carcinoid tumours and islet cell tumours of the pancreas reacted immunohistochemically to PSAP. We investigated 50 cases immunohistochemically comprising 44 carcinoids of the G-I tract, 3 of the bronchus, 1 each of the ovary, kidney and middle ear. PSAP positive cases were, 30 in G-I tract, one each in ovary and kidney. Eighty percent of tumours of hindgut origin were positive. Apart from the immunohistochemical study, the content of PSAP in preoperative serum and tumour tissue was estimated in a case with a rectal carcinoid. Extremely elevated PSAP was confirmed in both the serum and tumour tissue. Neuroendocrine tumours such as pheochromocytoma, medullary thyroid carcinoma, and islet cell carcinoma were investigated as controls. No cells immunoreactive to PSAP were observed in these control cases. Prostate specific antigen was definitely negative in carcinoids. We would emphasize that PSAP may be an excellent marker of carcinoids especially when derived from hindgut.