DOES TRANSURETHRAL MICROWAVE THERMOTHERAPY HAVE A DIFFERENT EFFECT ON PROSTATE CANCER THAN ON BENIGN OR HYPERPLASTIC TISSUE? ANIS A. KHAIR, ANNA PACELLI, KENNETH A. ICZKOWSKI, LIANG CHENG, FEDERICO A. CORICA, THAYNE R. LARSON, ALBERTO CORICA, AND DAVID G. BOSTWICK ABSTRACT Objectives. Transurethral microwave thermotherapy is useful for the treatment of benign prostatic hyperplasia, but its effect on cancer is not documented. We analyzed the pathologic changes occurring after microwave thermotherapy in whole mount radical prostatectomy specimens from patients with cancer. Methods. Nine patients scheduled for radical prostatectomy for clinically localized prostate cancer were treated with transurethral microwave thermotherapy (Urologix Targis System). Patients ranged in age from 64 to 72 years (mean 68). Seven patients underwent prostatectomy 4 to 90 hours after thermotherapy, and 2 other patients underwent prostatectomy 12 months after thermotherapy. Whole mount totally embedded prostates were mapped for necrosis and cancer, and the volume of each was measured by the grid method. Results. Pathologic stages were T2a (n = 4), T2b (n = 4), and T3b (n = 1). The prostates from patients who underwent radical prostatectomy within 4 to 90 hours of thermotherapy had a mean prostate weight of 47.4 g (range 19.5 to 70.3). Each consistently showed hemorrhagic necrosis and tissue devitalization without significant inflammation. Necrosis involved contiguous areas of benign epithelium, stroma, and cancer without skip areas. The mean volume of necrosis was 8.8 cc (range 1.4 to 17.8), and the mean percentage of the prostate involved by necrosis was 22% (range 3% to 39%). The necrosis was symmetric around the urethra in 6 of 7 cases. Urethral dilation was observed in 3 patients, and the mean maximum radial distance of necrotic tissue was 1.4 cm (range 0.6 to 1.8). Necrotic change was noted in 80% to 100% of the volume of cancer in 4 cases, 40% to 60% in 2 cases, and 5% in 1 case. The prostates from the 2 patients who underwent radical prostatectomy 12 months after thermotherapy had a mean weight of 88 g (55 and 121 g, respectively). Each showed periurethral fibrosis, nonspecific chronic inflammation, and squamous metaplasia of the urothelium. The mean volume of necrosis remaining was 0.2 cc. The mean percentage of the prostate involved by necrosis 1 year after thermotherapy was less than 1%. There was some reabsorption of dead tissue. The mean maximum radial distance of the necrotic tissue was 0.4 cm (0.2 and 0.7 cm, respectively). The prostatic urethra had viable and partially denuded urothelium in all cases. Conclusions. Microwave thermotherapy is clinically useful for ablation of benign prostate and cancer contiguous to the urethra, resulting in hemorrhagic necrosis with minimal damage to the urethra. There was no apparent differential morphologic sensitivity of benign prostatic tissue, hyperplastic tissue, or cancer to thermotherapy. UROLOGY 54: 67–72, 1999. © 1999, Elsevier Science Inc. P rostate cancer is the second leading cause of cancer death in American men, with an esti- mated 179,300 new diagnoses and 37,000 deaths in 1998. 1 Surgery and radiation therapy are the mainstays of treatment for localized and advanced prostate cancer. Although these treatments are beneficial, they carry significant morbidity and complications. 2 Microwave thermotherapy is a minimally inva- sive procedure that ablates human prostatic tis- sue. 3,4 Microwave hyperthermia was used success- fully on dog and human prostates, 5 although human clinical trials for benign prostatic hyperpla- sia did not start until this decade. 4 To our knowledge, the effect of thermotherapy The spouse of T. R. Larson holds stock in Urologix, Inc. From the Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota; Department of Urology, Mayo Clinic, Scottsdale, Arizona; and Universidad Nacional de Cuyo, Mendoza, Argentina Reprint requests:  Bostwick Laboratories, 6722 Patterson Avenue, Richmond, VA 23226 Submitted: October 26, 1998, accepted (with revisions): Janu- ary 13, 1999 ADULT UROLOGY © 1999, ELSEVIER SCIENCE INC. 0090-4295/99/$20.00 ALL RIGHTS RESERVED PII S0090-4295(99)00038-2 67