Mucinous adenocarcinoma of the prostatic urethra:
Case report and literature review
Yun-Rui Wu1, Po-Cheng Chen12, Shih-Hao Liu2
1Department of Urology, 2Department of Pathology, En Chu Kong Hospital, New Taipei city, Taiwan
Mucinous adenocarcinoma of urothelial origin is extremely rare and should be must be differentiated from other mucinous tumors. It has important diagnostic, therapeutic, and prognostic implications.
This 68-year-old male had been diagnosed with benign prostate hyperplasia and received transurethral resection of the prostate (TURP) last year. Transrectal ultrasound of the prostate showed no abnormal lesion and pre-operative prostate/adenoma volume of 41.9/13.1 grams. Pre-operative PSA level was 1.82 mg/dL. It showed grossly normal with resected prostate tissue of 6.9 grams during the operation. Pathology reported nodular hyperplasia but abundant mucin material and small aggregates of histiocytes seen in the specimen. No definite malignancy was identified. LUTs improved a lot after the operation.
However, intermittent gross hematuria with clots and mucin was noted 6 months later. Increasing darkly reddish mucous caused acute urine retention. He was admitted for TURP again, and multiple mucinous lesion was noted near bladder neck. Pathology revealed mucinous adenocarcinoma, in favor of urothelial origin from prostatic urethra. Microscopically, sections show a mucinous adenocarcinoma which is characterized by large pools of mucin lined by pseudostratified or tall columnar cells with areas of mucin dissecting into the prostatic stroma forming pools. The tumor cells are immunoreactive for CK7, CK20, CK34BE12 and negative for PSA. Based on morphology and immunohistochemistry, a mucinous adenocarcinoma of urothelial origin (prostatic urethra) is considered. A computed tomoghraphy scan of abdomen and pelvis showed multiloculated cystic lesion involving the prostate, seminal vesicle and protruding into the urinary bladder, consistent with the mucinous tumor. A laparoscopic radical prostatectomy was performed. The final pathology revealed a mucinous adenocarcinoma of prostatic urethra which involves transitional area and left seminal vesicle and penetrates the prostatic capsule into the extraprostatic fat. Neither lymphadenopathy nor distal metastasis is found. The result indicates pT3N0.
Primary and secondary mucinous tumors of the prostate are really rare, let alone mucinous adenocarcinoma of the prostatic urethra. Less than 20 cases were reported to date[1-5].
In 1996, Tran and Epstein reported the first two cases of mucinous adenocarcinoma arising from the prostatic urethra. Osunkoya AO et al. reviewed 15 cases of prostatic urothelial-type adenocarcinoma from 70000 prostate consults from 1990 to 2006, with incidence of below 0.2%. The most common symptoms are mucusuria and hematuria, causing urinary obstruction. Since the tumor arising from the prostatic urethra rather than luminal cells of prostatic ducts, the PSA levels usually do not elevate. In pathophysiology, mucinous adenocarcinoma of the prostatic urethra originates from urethritis glandularis or glandular metaplasia of the prostatic urethra with malignant transformation. Histologically, the tumor is characterized by large pools of mucin lined by pseudostratified or tall columnar cells with areas of mucin dissecting into the stroma forming pools. Mucinous adenocarcinoma of the prostatic urethra is typically immunoreactive for CK7, CK20, CK34BE12, CEA and negative for PSA, PSAP.  The standard treatment includes consolidative surgery, radiotherapy and chemotherapy. Patients with high risk should received regular follow-up including chest image, abdominal and pelvic MRI/CT every 3-6 months in the first 2 years and then yearly. According to Osunkoya AO et al., 8 men (53.3% in total 15 patients) died of the disease at an average of 49.2 months from presentation. 
The differential diagnoses include mucinous adenocarcinoma of the prostate, prostatic adenocarcinoma with mucinous features and secondary tumors. Mucinous adenocarcinoma of the prostate, with the highest incidence among these tumors, nearly 0.2%, is defined by the presence of at least 25% of the tumor composed of glands with extraluminal mucin, so the diagnosis can only be made in radical prostatectomy specimens. If the extraluminal mucinous component is less than 25% in radical prostatectomy specimens, found in prostate needle core biopsies or transurethral resection of the prostate specimens, it would be diagonosed as prostatic adenocarcinoma with mucinous features. Besides, the most common secondary tumors could directly extend or metastasis from either colonic or bladder primaries.
Here we would like to share our uncommon case and review the associated literatures to give a whole picture of the disease in differential diagnosis, immunohistochemistry, treatment and the importance of correct identification.