Diagnosis of carcinoid-like metastatic prostatic carcinoma by an immunoperoxidase method.

An unusual case of carcinoma of the prostate with metastases is described. the prostate and the metastases showed adenocarcinoma with carcinoid-like areas. A tumor with the same histologic features was found at the tip of the appendix and proved to be metastatic. The possibility of primary carcinoid of the prostate was considered; however, Fontana-Masson stain and electron microscopy failed to confirm this. Immunoperoxidase stain for prostatic acid phosphatase was done on the prostate and metastases. This stain is specific for tissues of prostatic origin. The stain was positive in the carcinoid-like areas, indicating that it was not a true carcinoid but rather prostatic carcinoma with a carcinoid-like pattern. Apparently, this is the first case of a metastatic prostatic carcinoma showing carcinoid-like areas that were positive for prostatic acid phosphatase.