Phyllodes tumor of the prostate with exuberant glandular hyperplasia

Reported herein is an unusual case of prostatic phyllodes tumor with exuberant glandular hyperplasia that led to misdiagnosis of adenocarcinoma. The tumor was detected in a 52-year-old man who had a 1 year history of dysuria. Adenocarcinoma of the prostate was diagnosed from a needle biopsy specimen. The patient received hormonal therapy for 6 months and underwent radical prostatectomy. Histologically, the tumor had an atypical stromal cell proliferation and elongated slit-like glands characteristic of a phyllodes tumor. The tumor was also accompanied by a florid proliferation of small acini, most of which lacked basal cells, a common manifestation of adenocarcinoma in the overall tumor area. The following features of the resected tumor were helpful for concluding that these acini were benign: lack of cytological anaplasia in spite of structural atypia, presence of scattered basal cells confirmed by immunohistochemistry (high-molecular-weight cytokeratin), and histological transition from these acini to apparently benign slit-like glands. The final diagnosis was then made as 'phyllodes tumor of the prostate with exuberant glandular hyperplasia'. Atypical stromal cells might provide a clue for the recognition of this rare tumor at initial diagnosis by needle biopsy.