[A case of prostate cancer with cyst formation]

A 73-year-old man with the complaint of dysuria of 2 years' standing was admitted to our hospital for further examination of an intrapelvic cystic mass, 8.6 cm in diameter, detected incidentally by abdominal ultrasonography. The serum concentration of prostate specific antigen (PSA) was elevated to 44.9 ng/ml. Pelvic computed tomography (CT) and magnetic resonance imaging (MRI) revealed a cystic mass with an irregular thick cyst wall posterior to the urinary bladder originating from the prostate. Transrectal needle biopsy presented a moderately differentiated adenocarcinoma of the prostate. The bloody fluid of the cyst obtained by transperineal aspiration contained a significantly increased level of PSA, but no cancer cells were detected by cytological examination. Total prostatectomy was performed under the diagnosis of clinical stage C (cT3N0M0) prostate cancer. Pathological diagnosis was that cancer cells were present in the prostate tissue and had partly infiltrated the cyst wall. These results suggest that the present cyst was associated with the development of prostate cancer as a pseudocyst without an epithelial lining. The patient has remained free from the disease for over ten months. We review 56 cases of this rare condition that have been reported in Japan.