A treatment for prostate cancer that uses microwaves to heat the prostate gland and destroy cancerous cells was found to be safe and effective.

Researchers tested the therapy in 25 prostate cancer patients who had failed conventional radiation therapy. The experimental treatment, known as interstitial microwave thermal therapy, was delivered through five antennae inserted beneath the skin under ultrasound guidance.

The doctors were able to heat the prostate to the cell-killing temperature of 55 degrees Centigrade (131 degrees Fahrenheit) while keeping temperatures in the urethra and rectum at a safe 42 degrees C (107 degrees F). The procedure required 2.5 hours of operating time, on average.

Before treatment, half of the patients had PSA levels above 6.69 nanograms per milliliter (ng/mL). Levels of PSA, a protein produced by the prostate, are used to screen for cancer. A PSA level of less than 2-4 ng/ml is considered normal.

At 24 weeks after therapy, 52% of patients had achieved PSA levels of 0.5 ng/ml or less. An additional 40% of patients had PSA levels between 0.51 and 4 ng/ml, the researchers note.

Patients also had biopsies -- a test in which a sample of tissue is removed and checked for cancer -- before the treatment and 24 weeks after treatment.

The rate of cancer-free biopsies among the patients at 24 weeks was 64%. There were no major complications with the microwave treatment, and minor complications usually resolved within 3 months of therapy.

Because prostate cancer varies in its aggressiveness and patients with disease that has not spread beyond the prostate can survive for long periods of time without symptoms, the researchers suggest that a treatment option with a low side-effect profile is highly desirable.

However, they add, longer-term follow-up in larger patient groups is required to confirm the results before microwave therapy can be considered as an option for treating prostate cancer.

The Journal of Urology November 2001;166:1707-1714