Mucinous adenocarcinoma of urinary bladder type arising from the prostatic urethra. Distinction from mucinous adenocarcinoma of the prostate.

We describe two cases of mucinous adenocarcinomas involving and confined to the prostate and originating from the prostatic urethra. These cases were identical to adenocarcinomas arising within the urinary bladder and differed from mucinous adenocarcinoma of the prostate. In both cases, an in situ adenocarcinoma component was identified in the overlying prostatic urethra. In one case the in situ adenocarcinoma arose in a villous adenoma of the urethra. Both cases contained lakes of mucin lined by tall columnar epithelium with varying degrees of cytologic atypia, and one case had mucin-positive signet cells. In contrast, mucinous adenocarcinomas of the prostate demonstrate tubules and cribriform glands floating within mucin; mucin-positive signet cells are rare. Both tumors were negative immunohistochemically for prostate-specific antigen and prostate-specific acid phosphatase and positive for carcinoembryonic antigen. One case was treated by radical prostatectomy, and the patient was without evidence of disease with short follow-up. Following simple prostatectomy, the other patient did not undergo definitive therapy for several years, at which point the tumor had progressed locally to an advanced stage. In terms of therapy, the distinction between mucinous adenocarcinoma or urinary bladder-type arising in the prostate depicted within the current study and mucinous adenocarcinoma of the prostate is significant.