NEW YORK (Reuters Health) - A patch that delivers estrogen through the skin may prove useful in treating advanced cases of prostate cancer, preliminary research suggests.

In a study of 13 prostate cancer patients who were given the Fem7 estrogen patch, UK researchers found that the therapy substantially lowered the men's testosterone levels.

Because testosterone helps fuel the growth and spread of prostate tumors, men with more-advanced prostate cancer commonly receive drugs called LHRH analogues that block the body's production of the hormone.

Estrogen patches have the potential to lower testosterone levels with a lesser risk of such side effects, according to the researchers on the new study, led by Dr. Ruth E. Langley of Imperial College London.

These early results, Langley noted, at least confirm that estrogen patches lower patients' testosterone to the desirable "castrate" levels.

"Therefore these patches show promise as a potential therapy for men with prostate cancer," Langley told Reuters Health.

The findings, published in the journal BJU International, are based on 13 men who are part of a larger trial designed to compare estrogen patches with LHRH therapy in treating prostate cancer. The researchers followed the effects of the Fem7 patch on the men's testosterone levels over 12 weeks.

The question of whether the patch should hold a place in the prostate cancer treatment arsenal requires further study, according to Langley.

"Transdermal estrogen therapy," the researcher said, "is a novel and potentially cost-effective approach to androgen (testosterone) deprivation therapy."

"Large long-term studies are required to assess its effect on prostate cancer and side effect profile compared to LHRH therapy."