Mucin-Producing Urothelial-Type Adenocarcinoma of the Prostate (a Case Report and Review of the Literature)

DISCUSSION

Adenocarcinoma arising in the male urethra can originate from urethritis glandularis of the urothelium and/or squamous mucosa, especially when the metaplasia is of an intestinal type. Other sources include periurethral structures such as Cowper's (bulbourethral) or Littre's glands. It may be quite difficult to determine the source of these tumors as they may be diagnosed late in the course of the disease and after telltale precursor lesions have been obliterated by the growing mass.^[1] Tran et al.^[2] reported that these tumors most likely arise from malignant transformation of the urethritis glandularis involving the urothelium lining the prostatic urethra or proximal prostatic ducts, followed by the development of adenocarcinoma in situ and invasive adenocarcinoma.

Establishing the correct diagnosis of urothelial-type adenocarcinoma involving the prostate is extremely important for several reasons. Correct diagnosis can prevent patients being subjected to extensive and invasive investigations to exclude the presence of a primary tumor in their gastrointestinal tract. It may be possible to avoid these investigations, the discomfort and risks associated with them, and the potential delay in the initiation of treatment if the correct diagnosis had been established at the time of prostate biopsy or transurethral resection. In addition, establishing the correct diagnosis will prevent the potential initiation of inappropriate hormone therapy that might occur if the tumor were to be misconstrued as a variant of acinar-type prostatic adenocarcinoma. The histopatholical changes in mucin-producing urothelial-type adenocarcinoma of the prostate are similar to conventional prostatic adenocarcinoma with mucin producing and secondary adenocarcinoma involving the prostate. It is very difficult to make a correct diagnosis only from a histopathological examination. An immunohistochemical panel mainly including PSA and CEA can be very helpful in establishing the correct diagnosis.

Conventional prostatic adenocarcinoma that is mucin-producing mainly includes mucinous carcinoma (MC), signet-ring cell carcinoma (SRCC) and mucinous carcinoma with signet-ring cells (MCSRC). P1 Saito et al. ^[4]reported that the positive rates for serum PSA in these tumors were 77.8%, 33.3% and 0% respectively, and others have indicated that the positive rates for immunohistochemical staining of PSA is 90.3%, 81.8% and 60.3% respectively.131 However the urothelial-type adenocarcinoma of the prostate, is quite different. Immunohistochemically, our case and the four published cases all showed negative findings for PSA, but were positive for CEA. In radical prostatectomy specimens, the diagnosis of mucin-producing urothelial-type adenocarcinoma of the prostate may be more apparent, given the greater likelihood of finding precursor lesions such as glandular metaplasia of the urothelium, or urethritis glandularis, and adenocarcinoma in situ.

To establish the correct diagnosis for mucin-producing urothelial-type adenocarcinoma of the prostate one must exclude the presence of a primary tumor in the gastrointestinal tract. Curtis et al^[5]. Reported that an immunohistochemical panel which included CK7, CK20, 34bE12, PSA and CEA was very helpful in establishing the correct diagnosis, especially distinguishing between a urothelial-type adenocarcinoma and secondary adenocarcinoma of colonic origin involving the prostate. In their report, positive results for CEA, CK7, 34bE12 and negative findings for PSA indicated a primary mucin-producing urothelial-type adenocarcinoma of the prostate. In our case, we performed an abdominal CT, colonoscopy, thorax CT and lumber MRI to completely exclude secondary adenocarcinoma.

The rarity of urothelial-type adenocarcinoma involving the prostate prevents making any conclusions with respect to clinical characteristics, behavior and treatment, other than to indicate that hormonal therapy would be inappropriate. The first patient reported in the literature was a 73-year-old man treated by radical prostatectomy who remained well without evidence of métastasés through one year of follow-up. The second patient was a 68-year-old man treated by a simple retropubic prostatectomy with recurrence of the tumor 4 years later that was treated with radiation therapy resulting in a modest response. The third patient treated by TURP, died 9 months later with liver métastasés. The fourth patient was treated by radical prostatectomy and remained disease-free for over 16 months of follow-up.^[5]

In summary, we have described one additional case of urothelial-type adenocarcinoma involving the prostate that had arisen in the prostatic urethra and/or proximal prostatic ducts. The documentation of more cases of urothelial-type adenocarcinoma involving the prostate is required to strengthen the contention that they arise in the prostatic urethra or proximal prostatic ducts, as well to determine the diagnostic standards, clinical behavior and establish optimal treatment.