Purpose: To study the clinical presentation and pathological features of secondary colonic adenocarcinoma of the prostate.
Materials and methods: Six cases of colonic adenocarcinoma extending into the prostate were retrieved from the surgical pathology and autopsy files of the period 1985-1999. Immunostaining for prostatic acid phosphatase (PAP), prostate specific antigen (PSA), cytokeratin 7 (CK7), cytokeratin 20 (CK20) and carcinoembryonic antigen (CEA) was carried out in all cases. Clinical charts were also reviewed.
Results: Secondary colonic carcinoma spread into the prostatic stroma and along the prostatic ducts. In all four surgical cases, patients with a known history of rectal carcinoma presented with symptoms of urinary obstruction after 12 to 36 months of being free of recurrent or metastatic disease. In three surgical cases the secondary carcinoma involved the prostatic urethra in a form mimicking endometrioid carcinoma, which led to an incorrect diagnosis of prostatic endometrioid carcinoma in one case. The tumor cells were immunoreactive to CK20 and CEA and not reactive to CK7, PAP and PSA.
Conclusions: Colonic carcinoma involving the prostate may mimic prostatic duct carcinoma due to the ductal and urethral involvement. Using a panel of immunostaining and clinical history is helpful in the differential diagnosis.