Prostatic ductal adenocarcinoma mimicking villous adenoma of the urethra

Abstract

Dear Editor, Prostatic ductal adenocarcinoma (PDA) is a rare variant of a prostatic adenocarcinoma, accounting for less than 1% [5]. Usually, PDAs grow in irregular complicated papillary or cribriform pattern, of which nuclear atypia is marked [5]. We report a case of PDA with bland cytological and structural atypia mimicking villous adenoma, suggesting a diagnostic pitfall. A 73-year-old man presented with a complaint of hematuria. A digital rectal examination revealed normal-sized prostate with no nodules, and the serum level of prostatespecific antigen (PSA) was within normal range. Urine cytology showed a few clusters composed of atypical cells with mildly increased N/C ratio and irregular nuclei, suspicious of malignancy. Ultrasonography characterized a tumor in the neck of the urinary bladder, 1.8 cm in maximal diameter (Fig. 1a, arrow), while urethrocystoscopy demonstrated a papillary tumor protruding into the prostatic urethra. Transurethral resection of the tumor was performed. Histologically, the resected specimen showed tumor fragments mainly comprised of simple papillary-growing components associated with a fibrovascular stalk, similar to villous adenoma (Fig. 1b). Serrated and cribriform figures were partially seen. The tumor cells appeared as tall columnar cells with pseudostratified nuclei and abundant cytoplasm (Fig. 1c). Cytological atypia was characteristically minimal. Cytoplasmic mucin was not detected by periodic acid-Schiff or Alcian blue staining. Immunohistochemically, the tumor cells diffusely expressed PSA (Fig. 1d) and androgen receptor and focally expressed prostatic acid phosphatase. Furthermore, α-methylacylCoA racemase (P504S) and prostate-specific membrane antigen were weakly positive, but cytokeratin (CK) 7 and CK20 were negative. Ki-67 (MIB-1) positivity was approximately 20%. Transrectal needle biopsy of the prostate was performed, and one of the six specimens demonstrated conventional acinar adenocarcinoma with a Gleason score of 3+3=6. The patient received hormonal therapy, and there was no evidence of local recurrence or distant metastasis 1 year after the tumor resection. PDA was first described as endometrial carcinoma of the prostatic utricle by Melicow and Pachter in 1967 [4]. The carcinoma has now been confirmed to originate from the prostatic duct, not derived from the Mullerian duct. The tumor growth can be subdivided into two patterns: centrally located papillary tumor protruding into the prostatic urethra such as this case, and peripherally located tumor diffusely involved in the transitional or peripheral zone of the prostate [5]. Histologically, tall columnar epithelium with pseudostratified nuclei and eosinophilic or amphophilic cytoplasm proliferate in a papillary and tubulopapillary fashion, resembling an endometrial carcinoma, and are nominated as type A. Type B shows cribriform patterned or solid growth with frequent comedonecrosis and marked nuclear atypia. Type A almost matches with adenocarcinoma of the primary prostatic ducts, and type B with adenocarVirchows Arch (2006) 449:597–599 DOI 10.1007/s00428-006-0290-6